Co-reporter:Shalene Xue Lin Goh, Hian Kee Lee
Journal of Chromatography A 2017 Volume 1488(Volume 1488) pp:
Publication Date(Web):10 March 2017
DOI:10.1016/j.chroma.2017.01.081
•New approach on hollow fiber-mediated liquid-phase microextraction was explored.•A bundled hollow fiber array was used as a novel extraction device.•Improved analytical performance was achieved in the extraction of estrogens.•Raman spectroscopy proved the hollow fiber played no sorptive extraction role.•The extraction technique has the potential to be automated.A bundled hollow fiber array (BHF)-liquid-phase microextraction (LPME) approach has been developed for the ultra-high performance liquid chromatography tandem mass spectrometric determination of estrone, 17β-estradiol, estriol, and 17α-ethinylestradiol. The BHF was dipped in n-octanol to impregnate only the wall pores of the hollow fibers without deliberate loading of extractant solvent in the lumens, before placing it in the sample for extraction. Parameters influencing extraction efficiency, such as number of bundled hollow fibers, type of extraction and desorption solvent, agitation mode, extraction temperature and duration, and the salting out effect were examined. Under the most favourable experimental conditions, the enrichment factors were between 77 and 137-fold for the target compounds. The developed method offered high sensitivity and reproducibility. Low limits of detection and limits of quantification were achieved, i.e., between 0.251 and 0.440 ng/L, and 0.995 and 1.82 ng/L, respectively. Good intra and inter-day precision were obtained with relative standard deviations (RSDs) of less than 9%. BHF-LPME provided a new perspective on using membrane solvent-supported hollow fiber-mediated LPME. Raman spectroscopy was also introduced in this study to reaffirm that the polypropylene BHF did not play any role in the extraction; only the solvent was responsible.
Co-reporter:Seyed Mohammad Majedi, Hian Kee Lee
Journal of Chromatography A 2017 Volume 1486(Volume 1486) pp:
Publication Date(Web):24 February 2017
DOI:10.1016/j.chroma.2016.06.079
•One-step, combined microextraction technique for atmospheric aliphatic amines.•Simultaneous derivatization and solvent-based extraction of amines in PM2.5.•High recovery and enrichment with the aid of vortex agitation and RGO sorbent.•High sensitivity and selectivity by derivatization of amines and GC–MS analysis.•Successful application to PM2.5 filter sample analysis with good reproducibility.Short-chain aliphatic amines are ubiquitous in the atmospheric environment. They play an important role in the formation and growth of atmospheric particles. As such, there is a pressing need to monitor these particle-bound compounds present at trace quantities. The present work describes an efficient, one-step microextraction technique for the preconcentration and detection of trace levels of 10 aliphatic amines on fine particles (particulate matter of 2.5 μm or less (PM2.5)) in the atmosphere. After extraction of amines from particles in acidified water samples, carbon-based sorbents (in dispersive solid-phase extraction mode), and vortex agitation were utilized for simultaneous derivatization-extraction and dispersive liquid–liquid microextraction. The approach significantly increased the recoveries and enrichment of the amine derivatives. This one-step, combined technique is proposed for the first time. Several influential factors including type and concentration of derivatization reagent (for gas chromatographic separation), type of buffer, sample pH, types and volumes of extraction and disperser solvents, type and amount of sorbent, vortex time and temperature, desorption solvent type and volume, and salt content were investigated and optimized. Under the optimum conditions, high enrichment factors (in the range of between 307 and 382) and good reproducibility (relative standard deviations, below 7.0%, n = 5) were achieved. The linearity ranged from 0.1 μg/L–100 μg/L, and from 0.5 μg/L–100 μg/L, depending on the analytes. The limits of detection were between 0.02 μg/L (corresponding to ∼0.01 ng/m3 in air) and 0.09 μg/L (corresponding to ∼0.04 ng/m3 in air). The developed method was successfully applied to the analysis of PM2.5 samples collected by air sampling through polytetrafluoroethylene filters. The concentration levels of amines ranged from 1.04 to 4.16 ng/m3 in the air sampled.
Co-reporter:Maryam Lashgari, Yadollah Yamini, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2017 Volume 1513(Volume 1513) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.chroma.2017.07.046
•Eight polar and non-polar NAs were determined simultaneously in water samples.•Oxidative surface-modified ordered mesoporous was applied as μ-SPE sorbent.•An isotopically-labeled NA was used as internal standard.•Despite the complex nature of the matrices, negligible matrix effects were observed.The analysis and determination of N-nitrosamines (NAs) in water samples are challenging and demanding. In this study, a simple, reliable, and practical methodology is reported for the quantitative determination by gas chromatography-tandem mass spectrometry with electron impact ionization (EI) and triple quadrupole analyzer (GC-EI-MS/MS) of eight NAs after micro-solid-phase extraction (μ-SPE) from wastewater and swimming pool water. Thirty milligram of an ordered mesoporous carbonaceous material, oxidative surface-modified CMK-3, enclosed within a porous polypropylene membrane bag, were used as sorbent for μ-SPE. A central composite design approach was applied to optimize the μ-SPE parameters. An isotopically-labeled NA was used as internal standard. Under the optimized conditions, μ-SPE-GC-EI-MS/MS was validated for an NA concentration range of between 0.1–100 ng/mL. The precision of the method was evaluated and an average relative standard deviation of 4.8% (n = 8) for a standard solution spiked at 50 ng/mL of each NA was obtained. The limits of detection were measured to be in the range of 0.005–0.283 ng/mL. Domestic wastewater and swimming pool water samples were used to evaluate the applicability of the method. NAs were detected in swimming pool water and wastewater at concentrations of <2 ng/mL and 11 ng/mL, respectively.
Co-reporter:Christina Shu Min Liew, Xiao Li, and Hian Kee Lee
Analytical Chemistry 2016 Volume 88(Issue 18) pp:9095
Publication Date(Web):August 18, 2016
DOI:10.1021/acs.analchem.6b02056
A new sample preparation approach of combining a miniscale version of liquid–liquid extraction (LLE), termed miniscale-LLE (msLLE), with automated full evaporation dynamic headspace extraction (FEDHS) was developed. Its applicability was demonstrated in the extraction of several polycyclic aromatic hydrocarbons (PAHs) (acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene) from aqueous samples. In the first step, msLLE was conducted with 1.75 mL of n-hexane, and all of the extract was vaporized through a Tenax TA sorbent tube via a nitrogen gas flow, in the FEDHS step. Due to the stronger π–π interaction between the Tenax TA polymer and PAHs, only the latter, and not n-hexane, was adsorbed by the sorbent. This selectivity by the Tenax TA polymer allowed an effective concentration of PAHs while eliminating n-hexane by the FEDHS process. After that, thermal desorption was applied to the PAHs to channel them into a gas chromatography/mass spectrometric (GC/MS) system for analysis. Experimental parameters affecting msLLE (solvent volume and mixing duration) and FEDHS (temperature and duration) were optimized. The obtained results achieved low limits of detection (1.85–3.63 ng/L) with good linearity (r2 > 0.9989) and high enrichment factors ranging from 4200 to 14 100. The optimized settings were applied to the analysis of canal water sampled from an industrial area and tap water, and this methodology was compared to stir-bar sorptive extraction (SBSE). This innovative combined extraction–concentration approach proved to be fast, effective, and efficient in determining low concentrations of PAHs in aqueous samples.
Co-reporter:Liang Guo, Nurliyana binte Nawi, and Hian Kee Lee
Analytical Chemistry 2016 Volume 88(Issue 17) pp:8409
Publication Date(Web):July 29, 2016
DOI:10.1021/acs.analchem.6b01543
A fully automated headspace bubble-in-drop microextraction (automated HS-BID) method, coupled to gas chromatography/mass spectrometric (GC/MS) analysis, was developed for the analysis of nitro musks in environmental water samples. The entire procedure, including the extraction of the analytes by HS-BID and GC/MS analysis of the analyte-enriched solvent, was completely automated. In BID, a certain volume of air is introduced into the extraction solvent droplet, enlarging the surface area of the extraction solvent droplet in relation to the water sample without increasing its volume, significantly enhancing extraction efficiency. Compared to conventional single drop microextraction, the developed method has higher extraction efficiency due to the enlarged surface area of the extraction solvent droplet. Under the optimized conditions (1.0 mL of sample solution, using 1.0 μL of 1-octanol containing of 0.5 μL of air bubble, at 40 °C for extraction for 20 min), the automated HS-BID gave low limits of detections (between 0.012 and 0.042 μg/L), good linearity (from 0.1 to 20 μg/L and from 0.2 to 50 μg/L, with r2 between 0.9909 and 0.9958, depending on analytes), and good repeatability of the extractions (relative standard deviations, below 4.7%, n = 5). The developed procedure was applied to determine nitro musks in environmental water samples and was demonstrated to be efficient, labor-free, economical, and environmentally benign.
Co-reporter:Sheng Tang, Hong Zhang, and Hian Kee Lee
Analytical Chemistry 2016 Volume 88(Issue 1) pp:228
Publication Date(Web):November 28, 2015
DOI:10.1021/acs.analchem.5b04040
Co-reporter:Liang Guo, Shao Hua Chia, and Hian Kee Lee
Analytical Chemistry 2016 Volume 88(Issue 5) pp:2548
Publication Date(Web):January 28, 2016
DOI:10.1021/acs.analchem.5b03919
Dispersive liquid–liquid microextraction (DLLME) is an extremely fast and efficient sample preparation procedure. For its capability and applicability to be fully exploited, full automation of its operations seamlessly integrated with analysis is necessary. In this work, for the first time, fully automated agitation-assisted demulsification (AAD)-DLLME integrated with gas chromatography/mass spectrometry was developed for the convenient and efficient determination of polycyclic aromatic hydrocarbons in environmental water samples. The use of a commercially available multipurpose autosampler equipped with two microsyringes of different capacities allowed elimination or significant reduction of manpower, labor, and time with the large-volume microsyringe used for liquid transfers and the small-volume microsyringe for extract collection and injection for analysis. Apart from enhancing accessibility of DLLME, the procedure was characterized by the application of agitation after extraction to break up the emulsion (that otherwise would need centrifugation or a demulsification solvent), further improving overall operational efficiency and flexibility. Additionally, the application of low-density solvent as extractant facilitated the easy collection of extract as the upper layer over water. Some parameters affecting the automated AAD-DDLME procedure were investigated. Under the optimized conditions, the procedure provided good linearity (ranging from a minimum of 0.1–0.5 μg/L to a maximum of 50 μg/L), low limits of detection (0.010–0.058 μg/L), and good repeatability of the extractions (relative standard deviations, below 5.3%, n = 6). The proposed method was applied to analyze PAHs in real river water samples.
Co-reporter:Hui Ling Teo, Lingkai Wong, Qinde Liu, Tang Lin Teo, Tong Kooi Lee, Hian Kee Lee
Analytica Chimica Acta 2016 Volume 912() pp:49-57
Publication Date(Web):17 March 2016
DOI:10.1016/j.aca.2016.01.028
•μ-SPE coupled with IDMS for the measurement of carbamazepine.•The method is the first report of coupling μ-SPE with IDMS.•μ-SPE is fast, time- and cost-effective, and environmentally friendly.•Highly precise and accurate IDMS measurement of carbamazepine in surface water.•The method facilitates the fast and accurate monitoring of anthropogenic markers.To achieve fast and accurate analysis of carbamazepine in surface water, we developed a novel porous membrane-protected micro-solid-phase extraction (μ-SPE) method, followed by liquid chromatography-isotope dilution tandem mass spectrometry (LC-IDMS/MS) analysis. The μ-SPE device (∼0.8 × 1 cm) was fabricated by heat-sealing edges of a polypropylene membrane sheet to devise a bag enclosing the sorbent. The analytes (both carbamazepine and isotope-labelled carbamazepine) were first extracted by μ-SPE device in the sample (10 mL) via agitation, then desorbed in an organic solvent (1 mL) via ultrasonication. Several parameters such as organic solvent for pre-conditioning of μ-SPE device, amount of sorbent, adsorption time, and desorption solvent and time were investigated to optimize the μ-SPE efficiency. The optimized method has limits of detection and quantitation estimated to be 0.5 ng L−1 and 1.6 ng L−1, respectively. Surface water samples spiked with different amounts of carbamazepine (close to 20, 500, and 1600 ng L−1, respectively) were analysed for the validation of method precision and accuracy. Good precision was obtained as demonstrated by relative standard deviations of 0.7% for the samples with concentrations of 500 and 1600 ng kg−1, and 5.8% for the sample with concentration of 20 ng kg−1. Good accuracy was also demonstrated by the relative recoveries in the range of 96.7%–103.5% for all samples with uncertainties of 1.1%–5.4%. Owing to the same chemical properties of carbamazepine and isotope-labelled carbamazepine, the isotope ratio in the μ-SPE procedure was accurately controlled. The use of μ-SPE coupled with IDMS analysis significantly facilitated the fast and accurate measurement of carbamazepine in surface water.
Co-reporter:Nyi Nyi Naing, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1427() pp:29-36
Publication Date(Web):4 January 2016
DOI:10.1016/j.chroma.2015.12.012
•Reduced graphene sheets were used in μ-SPE–HPLC–UV.•The sorbent was loaded with sodium dodecylsulfate (SDS) to prevent agglomeration in aqueous solution.•This procedure reveals good extraction efficiency for estrogens in water.•Four estrogens in canal water samples were determined by the developed method.A facile method of extraction using porous membrane protected micro-solid phase extraction (μ-SPE) with a graphene-based sorbent followed by high performance liquid chromatography–ultraviolet detector was developed. The reduced graphene oxide (r-GO) (1 mg), synthesized from graphite oxide, was enclosed in a polypropylene bag representing the μ-SPE device, which was used for the extraction of estrogens such as estrone, 17β-estradiol, 17α-ethynylestradiol and diethylstilbestrol in water. The r-GO obtained was identified and characterized by Fourier transform infrared, transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis. The sorbent was loaded with sodium dodecyl sulfate by sonication to prevent agglomeration in aqueous solution. With this method, low limits of detection of between 0.24 and 0.52 ng L−1 were achieved. For estrogen analysis a linear calibration range of 0.01–100 μg L−1 was obtained, with the coefficients of determination (r2) higher than 0.992. This proposed method was successfully applied to determine estrogens in water.
Co-reporter:Maryam Lashgari, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1432() pp:7-16
Publication Date(Web):5 February 2016
DOI:10.1016/j.chroma.2016.01.005
•μ-SPE was developed for extraction of trace levels of PFCAs in human plasma.•Central composite design was used for simultaneous optimization of effective parameters.•The relative recoveries of spiked PFCAs were in the range of between 87.58 and 102.45%Micro-solid phase extraction (μ-SPE), with liquid chromatography-tandem mass spectrometry has been developed for the determination of trace levels of perfluorinated carboxylic acids (PFCAs) in human plasma. The μ-SPE sorbent was surfactant-templated mesoporous silica. Extraction time, desorption time and salt concentration were chosen as the most effective parameters and were optimized simultaneously by use of central composite design. Under the optimized extraction conditions, good linearity in the range of 100 and 5000 ngL−1 was obtained with coefficients of determination of between 0.986 and 0.995. The limits of detection (at a signal to noise ratio of 3) were measured to be in the range of between 21.23 and 65.07 ngL−1, and limits of quantification (at a signal to noise ratio of 10) were in the range of between 70.77 and 216.92 ngL−1. The relative recoveries of spiked PFCAs in different samples were in the range of between 87.58 and 102.45%. As expected from the global distribution of PFCs, contaminations at low levels (less than 200 ngL−1) were detected (with the highest concentration recorded for perfluorooctanoic acid (PFOA)). Considering the complex nature of biological samples and the issue of matrix effects in the analysis of PFCAs, μ-SPE as an extraction method was shown to be advantageous; it combined extraction and concentration in one single step with no additional sample clean-up, and was able to remove significant matrix interferences.
Co-reporter:Liang Guo, Shufang Tan, Xiao Li, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1438() pp:1-9
Publication Date(Web):18 March 2016
DOI:10.1016/j.chroma.2016.02.008
•Automated dual-rail autosampler based dispersive liquid-liquid microextraction.•Use of large-volume syringe for fast solvent transfer and small-volume microsyringe for extract collection.•The approach is fully automated and efficient, and gives low LODs, good linearity and repeatability.An automated procedure, combining low density solvent based solvent demulsification dispersive liquid-liquid microextraction (DLLME) with gas chromatography–mass spectrometry analysis, was developed for the determination of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Capitalizing on a two-rail commercial autosampler, fast solvent transfer using a large volume syringe dedicated to the DLLME process, and convenient extract collection using a small volume microsyringe for better GC performance were enabled. Extraction parameters including the type and volume of extraction solvent, the type and volume of dispersive solvent and demulsification solvent, extraction and demulsification time, and the speed of solvent injection were investigated and optimized. Under the optimized conditions, the linearity ranged from 0.1 to 50 μg/L, 0.2 to 50 μg/L, and 0.5 to 50 μg/L, depending on the analytes. Limits of detection were determined to be between 0.023 and 0.058 μg/L. The method was applied to determine PAHs in environmental water samples.
Co-reporter:Nyi Nyi Naing, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1448() pp:42-48
Publication Date(Web):27 May 2016
DOI:10.1016/j.chroma.2016.04.062
•Novel sorbent, cross-linked chitosan microspheres, was synthesized and used in μ-SPE.•Evaluation was carried out by μ-SPE coupled with GC–MS.•This procedure provides good extraction efficiency for BTEX-S from water.Chitosan (CS) microspheres were synthesized by the precipitation method and cross-linked with glutaraldehyde. The cross-linked CS microspheres (20 mg) were used as sorbents for the micro-solid phase extraction (μ-SPE) of benzene, toluene, ethylbenzene, xylenes and styrene (BTEX-S) from water. The μ-SPE device consisted of a sealed polypropylene envelope housing the microspheres for the evaluation of the extraction efficiency. Analysis was by gas chromatography-mass spectrometry (GC–MS). Under the optimized conditions, the method provided linearity range of between 0.5 and 50 μg L−1 with good correlation coefficients of between 0.985 and 0.998. The relative standard deviations of μ-SPE coupled with GC–MS were found to be between 2 and 3%. Method detection limits for BTEX-S were in the range of between 0.01 and 0.04 μg L−1 while the relative recoveries were in the range of between 59 and 97%. The proposed method is a cost effective, fast and environmentally friendly extraction technique with ease of operation and minimal usage of organic solvent.
Co-reporter:Nyi Nyi Naing, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1458() pp:25-34
Publication Date(Web):5 August 2016
DOI:10.1016/j.chroma.2016.06.056
•CS-GO was used in μ-SPE of five polybrominated diphenyl ethers in water.•Analytes in the extract were extracted thermally in a TDU coupled to the GC–MSD.•Lower molecular mass analytes were more amenable to be isolated and detected.A method of analyzing environmental contaminants in water based on micro-solid phase extraction (μ-SPE) followed by thermal extraction (TE) and a cold-trapping step, coupled with gas chromatography-mass selective detection (GC–MSD) was developed and validated. μ-SPE–TE– GC–MSD was employed in the determination of five polybrominated diphenyl ethers. The μ-SPE sorbent was chitosan-graphene oxide (CS-GO) composite, which was prepared by mixing CS and GO by means of ultrasonication. The CS in the composite was cross-linked with glutaraldehyde. After μ-SPE, the analytes in the extract were extracted thermally in a thermal desorption unit tube combined with a cooled injection system, coupled to GC–MSD. The extraction conditions were optimized for the detection of the target compounds in water. This method provided linearity ranges of between 0.1 and 20 μg L−1 (depending on the analytes), with coefficients of determination, r2, ≥0.9982. The calculated relative recoveries were between 71.52 and 96.15% whereas precision (based on % relative standard deviations) was between 3.54 and 11.36%. The method showed limit of detection and limit of quantification ranges of between 0.007 and 0.016 μg L−1, and between 0.023 and 0.054 μg L−1, for the two groups of analytes, respectively. The method was applied to the determination of the target analytes in water.
Co-reporter:Shalene Xue Lin Goh, Ankur Duarah, Lifeng Zhang, Shane A. Snyder, Hian Kee Lee
Journal of Chromatography A 2016 Volume 1465() pp:9-19
Publication Date(Web):23 September 2016
DOI:10.1016/j.chroma.2016.08.040
•An automated online SPE procedure was developed to extract steroid hormones.•Six estrogens and six glucocorticoids were studied.•Improved analytical performance was achieved.•Low sample volume and minimal analysis time were attained.•Isotopic standards helped to minimise matrix effects.The present work describes the development of a novel fully automated online solid phase extraction (SPE) coupled with high performance liquid chromatography-tandem mass spectrometry (LC–MS/MS) using negative electrospray ionisation (ESI) for the simultaneous determination of six estrogens and six glucocorticoids in water. Filtered water samples (5 mL) were preconcentrated on a HyperSep™ Retain PEP SPE cartridge, eluted in back-flush mode, and separated on an LC column before analysis by tandem mass spectrometry. The total analysis time for each sample was 17 min. Different experimental parameters such as the type of online SPE cartridge, loading flow rate, and composition of methanol in the loading phase were optimised. The intra-day repeatability of method ranged from 1.48 to 9.68% for all analytes, and the inter-day reproducibility ranged from 2.03 to 8.63% for all analytes, except for dexamethasone at 11.95%. These were calculated based on the peak area responses of the targeted analytes spiked at 50 ng/L in ultrapure water. The method also showed good linearity from 1 to 100 ng/L, with the limits of detection (LODs) ranging from 0.16 to 2.14 ng/L. The proposed method was applied to the analysis of municipal wastewater. This fully automated online SPE extraction coupled with LC–MS/MS method is effective and reliable to measure estrogens and glucocorticoids simultaneously due to its high throughput, relatively low solvent consumption, reusability of the online SPE cartridge, and reduction of manual labor.
Co-reporter:Maryam Lashgari, Hian Kee Lee
Journal of Colloid and Interface Science 2016 Volume 481() pp:39-46
Publication Date(Web):1 November 2016
DOI:10.1016/j.jcis.2016.07.029
•The surface of the CMK-3 was modified by carboxylic groups.•A hydrophobic/hydrophilic balance was created on surface.•The hydrophilicity of the surface was increased.•With limited access of the hydrophobic analytes, they could be eluted easily.•The modified surface showed the best performance for the extraction of analytes.The extraction and pre-concentration of N-nitrosamines (NAs) before their determination are mainly achieved by carbonaceous sorbents. However, the non-polar or relatively less polar NAs are strongly absorbed on the carbonaceous surface of the sorbent, leading to low extraction recoveries. In the present study, for the first time, CMK-3 and surfacemodified CMK-3 (O-CMK-3) were used to extract NAs from water. The CMK-3 surface was modified by oxidative treatment and different carboxylic groups were attached to create a hydrophilic/hydrophobic balance on the inert surface of the carbonaceous sorbent. The proposed sorbents were compared with 10 different kinds of commercial carbonaceous sorbents for the micro-solid phase extraction of eight NAs possessing a wide range of polarities. The best extraction results for both polar and non-polar NAs were obtained using O-CMK-3. Specifically, significant enhancements in the extraction of the nonpolar NAs were observed. For instance, extraction of up to 27.67 and 2.32 times greater were observed for N-nitrosodiphenylamine, and N-nitrosodimethylamine respectively, when O-CMK-3 was used instead of coconut charcoal sorbent.
Co-reporter:Seyed Mohammad Majedi, Hian Kee Lee
TrAC Trends in Analytical Chemistry 2016 Volume 75() pp:183-196
Publication Date(Web):January 2016
DOI:10.1016/j.trac.2015.08.009
•The species selectivity of the available techniques for the detection of nanoparticles (NPs) is reviewed.•Inductively coupled plasma mass spectrometry (ICP–MS) in combination with separation techniques provides the highest sensitivity.•The presence of ions and transformation of NPs can interfere with the detection of NPs.•NPs can be efficiently isolated from the ions with high enrichment and recovery by solid-phase extraction (SPE) and cloud point extraction (CPE).•Electrochemistry-based techniques can yield low limits of detection (LODs), but are not species selective.Nanosized materials such as metallic nanoparticles (MNPs) are currently used in industrial and consumer products, and concomitantly, their release into the environment is becoming a major concern because of their enhanced negative impacts on living organisms. Currently, studies are being conducted on the detection of trace and environmental levels of these materials, identification of sources, distribution, fate, and toxicological effects of these materials in nature, and also standardization of protocols for reliable risk assessment. Despite the efforts made so far, there is still a lack of sensitive and selective analytical platforms to enable the monitoring of ultratrace MNPs in their original states and discriminate between the NP and NP-containing ions in complex matrices. The current review describes the recent advances in the separation and quantification of MNPs with an emphasis on the species selectivity of the available techniques and their applicability to environmental samples.
Co-reporter:Sheng Tang, Yuepeng Chang, Wei Shen, Hian Kee Lee
Talanta 2016 Volume 154() pp:416-422
Publication Date(Web):1 July 2016
DOI:10.1016/j.talanta.2016.03.096
•(NTA-Ni)-layered double hydroxides was synthesized as a sorbent to extract Fe3+.•A selective extraction-dissolution-reaction approach has been developed for detection of Fe3+.•Through two steps, extraction and reaction, the detection signal was amplified.•Ion-exchange and reaction ensured the specificity of the method.•The dissolution of sorbent replaced the elution/desorption step, usually necessary in most solid-phase extraction.A highly selective method has been proposed for the determination of iron cation (Fe3+). (Nitriloacetic acid-nickel)-layered double hydroxide ((NTA-Ni)-LDH) was successfully synthesized and used as dissolvable sorbent in dispersive solid-phase extraction to pre-concentrate and separate Fe3+ from aqueous phase. Since Fe3+ has a larger formation constant with NTA compared to Ni2+, subsequently ion exchange occurred when (NTA-Ni)-LDH was added to the sample solution. The resultant (NTA-Fe)-LDH sol was isolated and transferred in an acidic medium containing potassium thiocyanate (KSCN). Since (NTA-Fe)-LDH could be dissolved in acidic conditions, Fe3+was released and reacted with SCN− to form an Fe-SCN complex. The resulting product was measured by ultraviolet-visible spectrometry for quantitative detection of Fe3+. Extraction factors, including sample pH, reaction pH, extraction temperature, extraction time, reaction time and concentration of KSCN were optimized. This method achieved a low limit of detection of 15.2 nM and a good linear range from 0.05 to 50 μM (r2=0.9937). A nearly 18-fold enhancement of signal intensity was achieved after selective extraction. The optimized conditions were validated by applying the method to determine Fe3+ in seawater samples.
Co-reporter:Sheng Tang, Yuepeng Chang, Guo Hui Chia, Hian Kee Lee
Analytica Chimica Acta 2015 Volume 885() pp:106-113
Publication Date(Web):23 July 2015
DOI:10.1016/j.aca.2015.05.029
•(EDTA-Ni)-layered double hydroxides were synthesized as a sorbent to extract Cu2+.•A selective extraction-release-catalysis approach has been developed for detection of Cu2+.•Through two steps, extraction and catalysis, the detection signal was amplified.•Ion-exchange, release and efficient catalysis ensured the high selectivity of the method.Copper is an important heavy metal in various biological processes. Many methods have been developed for detecting of copper ions (Cu2+) in aqueous samples. However, an easy, cheap, selective and sensitive method is still desired. In this study, a selective extraction-release-catalysis approach has been developed for sensitive detection of copper ion. Ethylenediaminetetraacetic acid (EDTA) chelated with nickel ion (Ni2+) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent in dispersive solid-phase extraction for the enrichment of Cu2+ at pH 6. Since Cu2+ has a stronger complex formation constant with EDTA, Ni2+ exchanged with Cu2+ selectively. The resulting sorbent containing Cu2+ was transferred to catalyze the 3,3′,5,5′-tetramethylbenzidine oxidation reaction, since Cu2+ could be released by the sorbent effectively and has high catalytic ability for the reaction. Blue light emitted from the oxidation product was measured by ultraviolet–visible spectrophotometry for the determination of Cu2+. The extraction temperature, extraction time, and catalysis time were optimized. The results showed that this method provided a low limit of detection of 10 nM, a wide linear range (0.05–100 μM) and good linearity (r2 = 0.9977). The optimized conditions were applied to environmental water samples. Using Cu2+ as an example, this work provided a new and interesting approach for the convenient and efficient detection of metal cations in aqueous samples.
Co-reporter:Zhenzhen Huang, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1401() pp:9-16
Publication Date(Web):3 July 2015
DOI:10.1016/j.chroma.2015.04.052
•A new application of MIL-101 for micro-solid-phase extraction was investigated.•The extraction towards organochlorine pesticides was optimized.•Efficient enrichment was achieved due to the porous structure of MIL-101.•The feasibility of analysis of real water samples was demonstrated.In this study, a metal-organic framework material, MIL-101, used as a micro-solid-phase extraction (μ-SPE) sorbent for efficient enrichment of five organochlorine pesticides (OCPs), including α-HCH, Aldrin, α-Chlordane, Dieldrin and p,p′-DDD from water samples, followed by gas chromatography–mass spectrometry, is reported. This study demonstrated a new application of MIL-101 using μ-SPE, an advantage of the latter being its ability to process complex aqueous matrices, due to the protection of the sorbent afforded by the hollow fiber membrane bag. Key factors affecting extraction efficiency were studied, including elution solvent, extraction and desorption time. Under the optimal extraction conditions, the calibration plots were linear from 0.05 to 50 ng/mL for α-HCH and p,p′-DDD, and 0.1 to 50 ng/mL for the other three analytes. The limits of detection were between 0.0025 and 0.016 ng/mL. The relative recoveries of the OCPs spiked into real water samples (at 5 ng/mL of each analyte) ranged from 87.6 to 98.6% with relative standard deviations of <10%.
Co-reporter:Sheng Tang, Guo Hui Chia, Hian Kee Lee
Journal of Colloid and Interface Science 2015 Volume 437() pp:316-323
Publication Date(Web):1 January 2015
DOI:10.1016/j.jcis.2014.09.038
•Magnetic core–shell Fe3O4@layered double oxide microspheres were synthesized and utilized as adsorbent.•2,5-Dihydroxybenzoic acid, as an emerging contaminant, was effectively removed by the adsorbent.•Due to the “memory effect”, the adsorbent showed high adsorption capacity and satisfactory recyclability.Magnetic core–shell Fe3O4@layered double oxide (Fe3O4@LDO) microspheres were synthesized and utilized as adsorbent in the removal of 2,5-dihydroxybenzoic acid (2,5-DHBA) from aqueous samples. Due to the “memory effect”, the microspheres showed higher adsorption capacity compared with Fe3O4@layered double hydroxide. The Fe3O4@LDO microspheres were easily recovered after the experiment via the application of a magnetic force. The effect of mass of Fe3O4@LDO, temperature and time on adsorption efficiency were investigated using batch experiments. Adsorption was in conformance with the Langmuir model, with a maximum adsorption capacity of 188.7 mg/g. Recyclability experiments indicated that adsorption efficiency did not decrease noticeably after 3 cycles of adsorption–calcination. The Fe3O4@LDO microspheres were evaluated by considering matrix-matched aqueous samples spiked with 2,5-DHBA. Under optimized conditions, 98.4% of the 2,5-DHBA analyte in the sample can be effectively removed from an aqueous solution within 4 h. The results indicate that Fe3O4@LDO microspheres have the potential to be employed as highly efficient, convenient, and low-cost magnetic adsorbents in the removal of 2,5-DHBA from water.
Co-reporter:Zhenzhen Huang, Pey Ee Chua, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1399() pp:8-17
Publication Date(Web):19 June 2015
DOI:10.1016/j.chroma.2015.04.028
•A carbonaceous coating material derived from polydopamine (C-PDA) is proposed.•The C-PDA coated stainless steel wire was applied as SPME fiber.•Extraction of organochlorine pesticides with the fabricated fiber was studied.•This method was proved to be suitable for analysis of environmental samples.A facile preparation route for coating a stainless steel fiber with carbonaceous material derived from polydopamine is reported in this work. The self-oxidation induced polymerization of dopamine in alkaline solution enables growth of polydopamine on the inert surface of the fiber. The robust adhesion of dopamine to metal oxides ensured sufficient stability of the polymer coating. After carbonization of the polymer coating, the obtained carbon coated fiber was utilized for solid-phase microextraction and exhibited effectiveness in the extraction of organochlorine pesticides (OCPs) from aqueous solution. Extraction time, agitation speed and salt addition were optimized. The possible interference of humic acid on the extraction of these analytes was also investigated. The results showed that most of the analytes could be detected efficiently in the presence of humic acid at a concentration of 20 mg/L. Under the optimized conditions, enrichment factors of 102–757 were obtained for the selected OCPs in aqueous solution. The proposed method provided low limits of detection (1.4–15 ng/L), good linearity (correlation coefficients > 0.9971) and acceptable precision (relative standard deviations < 16.3%).
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1408() pp:56-62
Publication Date(Web):21 August 2015
DOI:10.1016/j.chroma.2015.07.029
•Carbon nanotubes functionalized with chitosan was coated on porous membrane.•Coated membrane was used for microextraction of PCBs and PBDEs.•Optimization was by orthogonal array design.•The procedure was applied successfully to environmental aqueous samples.•Good linearity, and low LODs and RSDs% were achieved.Acid oxidized multi-walled carbon nanotubes (CNTs) functionalized with chitosan were coated on polypropylene membrane and used as sorbent to extract trace polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) from environmental water samples. The analytes were extracted by the hydrophobic interaction between analytes and the functionalized CNTs. The chitosan polymer coating also contributed to extraction efficiency. Microextraction conditions (different types of desorption solvent, extraction time, salt concentration, stirring rate and desorption time) were optimized by means of orthogonal array design (OAD). A mixed level OAD matrix, OA16 (41 × 212) was employed for the initial optimization. Based on the results of the first step, n-hexane was chosen as desorption solvent and 5 min was selected as desorption time. Extraction time, stirring rate and salt concentration were further optimized in the second step by an OA16 (45) matrix. Under the optimized conditions, calibration curves with coefficients of determination higher than 0.993 over the concentration range of 0.2 and 50 ng/ml. Low limits of detection (<0.60 ng/l) and acceptable reproducibility with relative standard deviations in the range of 0.17% and 5.01%, were achieved. The developed method was applied to extract PCBs and PBDEs from environmental water samples. The relative recoveries of the analytes spiked into the real water samples ranged from 85.6 to 104.1% at 0.2 ng/ml of each analyte, and from 82.4 to 98.6% at 2 ng/ml of each analyte.
Co-reporter:Zhenzhen Huang, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1414() pp:41-50
Publication Date(Web):2 October 2015
DOI:10.1016/j.chroma.2015.08.039
•Magnetic particles with a polydopamine and a carbon shell were prepared.•The two materials were successfully applied to the extraction of estrogens.•Orthogonal array design was used for optimization of the extraction performance.•The polydopamine coating was slightly superior to the carbon coating.Surface functionalization enabled by bioinspired polydopamine (PDA) is recognized as a convenient route for fabrication of multifunctional nanoparticles. In the present work, magnetic nanoparticles with polymer (Fe3O4@PDA) and carbon shell (Fe3O4@C) were prepared by self-oxidation of dopamine, and carbonization of the PDA coating. The performance of the two magnetic sorbents in the extraction and determination of four estrogens, estrone (E1), estradiol (E2), estriol (E3) and diethylstilbestrol (DES) from water samples in the form of magnetic solid-phase extraction was investigated. Orthogonal array design was utilized to facilitate the optimization of the proposed sample preparation approach. The highest extraction capabilities of the two sorbents were achieved under different experimental conditions. Fe3O4@PDA was shown to be superior to Fe3O4@C in the enrichment of estrogens, suggesting stronger interactions were established between the PDA coating and the target compounds. The extraction and desorption operations were enabled more conveniently by magnetic separation and the extracts were analyzed by high-performance liquid chromatography coupled with ultraviolet and fluorescence detection. The limits of detection achieved in the proposed method were in the range of 0.072–0.15 ng/mL for E1 and DES, and 0.0017–0.0062 ng/mL for E2 and E3. Good precision (>0.9995) was obtained with the linearity ranging from 0.2 to 100 ng/mL, and from 0.01 to 5 ng/mL. The method developed was assessed by analysis of the estrogens in tap water, drain water and bottled mineral water samples.
Co-reporter:Nyi Nyi Naing, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1423() pp:1-8
Publication Date(Web):4 December 2015
DOI:10.1016/j.chroma.2015.10.048
•Reduced graphene oxide/polyvinyl chloride sorbents immobilized in the membrane bag wall pores are used in EME.•This procedure exhibits good extraction efficiency for five phenolic compounds.•Phenolic compounds in river water samples were determined by the developed method.Electro membrane extraction-solid–liquid phase microextraction (EME-SLPME) was developed for the first time to determine phenolic contaminants in water. The extraction system consisted of a solid/liquid interface that permitted a three-phase microextraction approach involving an aqueous sample (donor phase): an organic solvent–sorbent within a membrane bag, and an organic solvent (extractant phase), operated in a direct immersion sampling system. The sorbent, reduced graphene oxide/polyvinyl alcohol, synthesized using graphene oxide and polyvinyl alcohol by dispersing the graphene oxide in polyvinyl alcohol and chemically reducing it in aqueous solution. The prepared sorbent was dispersed in 1-octanol and the solution was immobilized by sonication in the membrane bag wall pores which was in contact with the aqueous donor solution and organic extractant solvent (1-octanol) in the main bag itself. The analytes were transported by application of an electrical potential difference of 100 V across the sorbent/solvent phase from the aqueous sample into the organic extractant phase in the membrane bag. After extraction and derivatization, gas chromatography–mass spectrometry was used to determine the derivatized analytes. This proposed EME-LSPME procedure provided high extraction efficiency with relative recoveries up to 99.6%. A linearity range of between 0.05 and 100 μg L−1 with corresponding coefficients of determination (r2) of between 0.987 and 0.996 were obtained. The limits of detection were in the range of between 0.003 and 0.053 μg L−1. This proposed method was successfully applied to the extraction of phenolic contaminants from water sample.
Co-reporter:Nyi Nyi Naing, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2015 Volume 1426() pp:69-76
Publication Date(Web):24 December 2015
DOI:10.1016/j.chroma.2015.11.070
•Extraction with water-immiscible organic solvent followed by DSPE was carried out.•Amine functionalized graphene was used as sorbent in DSPE combined with in situ derivatization and GC–MS.•This procedure exhibits good extraction efficiency for acidic pharmaceuticals.•Five acidic pharmaceuticals in river water samples were determined by the developed method.A fast and low-cost sample preparation method of graphene based dispersive solid-phase extraction combined with gas chromatography–mass spectrometric (GC–MS) analysis, was developed. The procedure involves an initial extraction with water-immiscible organic solvent, followed by a rapid clean-up using amine functionalized reduced graphene oxide as sorbent. Simple and fast one-step in situ derivatization using trimethylphenylammonium hydroxide was subsequently applied on acidic pharmaceuticals serving as model analytes, ibuprofen, gemfibrozil, naproxen, ketoprofen and diclofenac, before GC–MS analysis. Extraction parameters affecting the derivatization and extraction efficiency such as volume of derivatization agent, effect of desorption solvent, effect of pH and effect of ionic strength were investigated. Under the optimum conditions, the method demonstrated good limits of detection ranging from 1 to 16 ng L−1, linearity (from 0.01 to 50 and 0.05 to 50 μg L−1, depending on the analytes) and satisfactory repeatability of extractions (relative standard deviations, below 13%, n = 3).
Co-reporter:Zhenzhen Huang, Hian Kee Lee
Talanta 2015 Volume 143() pp:366-373
Publication Date(Web):1 October 2015
DOI:10.1016/j.talanta.2015.05.006
•Surface modification of MIL-101 with Triton X-114 was investigated.•MIL-101 after modification was applied to dispersive solid-phase extraction.•Enhanced performance in extraction of estrogens was obtained.•Post-extraction derivatization coupled with GC–MS analysis was used.The research presented in this paper explored the modification and application of a metal-organic framework, MIL-101, with nonionic surfactant-Triton X-114 in dispersive solid-phase extraction for the preconcentration of four endocrine disrupting chemicals (estrone, 17α-ethynylestradiol, estriol and diethylstilbestrol) from environmental water samples. Triton X-114 molecules could be adsorbed by the hydrophobic surface of the MIL-101 crystals, and thus improved the dispersibility of MIL-101 in aqueous solution by serving as a hydrophilic coating. Cloud point phase separation from Triton X-114 accelerated the separation of extracts from the aqueous matrix. The proposed method combines the favorable attributes of strong adsorption capacity resulting from the porous structure of MIL-101 and self-assembly of Triton X-114 molecules. Post-extraction derivatization using N-methyl-N-(trimethylsilyl)trifluoroacetamide was employed to facilitate the quantitative determination of the extracts by gas chromatography–mass spectrometry. The main factors affecting the preparation of modified MIL-101, and extraction of the analytes, such as the amount of surfactant, the ultrasonic and vortex durations, solution pH and desorption conditions, were investigated in detail. Under the optimized conditions, the present method yielded low limits of detection (0.006–0.023 ng/mL), good linearity from 0.09 to 45 ng/mL (coefficients of determination higher than 0.9980) and acceptable precision (relative standard deviations of 2.2–13%). The surface modified MIL-101 was demonstrated to be effective for the extraction of the selected estrogens from aqueous samples, giving rise to markedly improved extraction performance compared to the unmodified MIL-101.
Co-reporter:Dandan Ge, Hian Kee Lee
Talanta 2015 Volume 132() pp:132-136
Publication Date(Web):15 January 2015
DOI:10.1016/j.talanta.2014.08.074
•An ultra-hydrophobic ionic liquid, [HMIM][FAP], was used for three-phase HF-LLLME of chlorophenols.•The proposed method was applied successfully to environmental aqueous samples.•Good linearity, and low LODs and %RSDs were achieved.An ultra-hydrophobic ionic liquid, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM][FAP]) was immobilized in the pores of a polypropylene hollow fiber for liquid–liquid–liquid microextraction (HF-LLLME) of chlorophenols (CPs) (4-chloro-3-methylphenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol). The analytes were first extracted from 10 ml of water sample into the ionic liquid membrane, and then were extracted back into 5 μl of sodium hydroxide aqueous solution in the hollow fiber channel. After extraction, the acceptor solution was directly injected into a high-performance liquid chromatographic system for analysis. Extraction parameters such as extraction time, salt concentration in the sample, the pH of the sample and acceptor phase, and stirring rate during extraction were investigated. The relative standard deviations of the analytes varied from 4 to 6%. Limits of detection of <0.5 ng/ml were obtained for the three analytes. The squared regression coefficients relating to the calibration curve were ≥0.9941. The proposed method was applied to the analysis of CPs in canal water.
Co-reporter:Maryam Lashgari, Chanbasha Basheer, Hian Kee Lee
Talanta 2015 Volume 141() pp:200-206
Publication Date(Web):15 August 2015
DOI:10.1016/j.talanta.2015.03.049
•µ-SPE was developed for trace levels of PFCAs in water samples.•Non-calcined silica ordered mesoporous material was used successfully as sorbent.•Parameters influencing extraction efficiency were investigated.•Limits of detection of ≤0.08 ng L−1 were obtained.•The method was successfully applied for river and rain water samples.In the present study, micro-solid phase extraction (µ-SPE) followed by liquid chromatography–triple tandem mass spectrometery (LC–MS/MS) was developed for the determination of perfluorocarboxylic acids (PFCAs) at trace levels in water samples. The µ-SPE device comprised of a porous polypropylene membrane bag containing 5 mg sorbent. The membrane bag acted as a clean-up filter and prevented matrix compounds from interfering with the extraction process. Analysis was carried out by LC–MS/MS in negative electrospray ionization mode. MS/MS parameters were optimized for multiple reaction monitoring. Calcined and non-calcined MCM-41, as silica-ordered mesoporous materials, were used as sorbents in µ-SPE for the extraction of five PFCAs—perfluoropentanoic acid (PFPA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA)—from aqueous media. The performances of these two sorbents were compared with other sorbents such as octadecylsilane (C18) modified silica, HayeSep-A, HayeSep-B, and Porapak-R. It was found that non-calcined MCM-41 showed better extraction performance for the analytes considered. Parameters influencing extraction efficiency, such as desorption time, extraction time, desorption solvent, and salt concentration, were investigated. The effect of the matrix on MS signals (suppression or enhancement) was also evaluated. Only minor effects on ionization efficiencies were observed. The developed method proved to be convenient and offered good sensitivity and reproducibility. The limits of detection ranged from 0.02 to 0.08 ng L−1, with a relative standard deviations between 1.9 and 10.5. It was successfully applied to the extraction of PFCAs in river and rain water samples. As expected from the ubiquitous nature of PFCAs, contamination at low levels was detected for some analytes in the samples (with the highest concentration recorded for PFOA). Satisfactory relative recoveries ranging between 64% and 127% at spiking levels of 10 ng L−1 of each analyte were obtained.
Co-reporter:Liang Guo and Hian Kee Lee
Analytical Chemistry 2014 Volume 86(Issue 8) pp:3743
Publication Date(Web):March 25, 2014
DOI:10.1021/ac404088c
An innovative automated procedure, low-density solvent based/solvent demulsification dispersive liquid–liquid microextraction (automated DLLME) coupled to gas chromatography–mass spectrometry (GC/MS) analysis, has been developed. The most significant innovation of the method is the automation. The entire procedure, including the extraction of the model analytes (phthalate esters) by DLLME from the aqueous sample solution, breaking up of the emulsion after extraction, collection of the extract, and analysis of the extract by GC/MS, was completely automated. The applications of low-density solvent as extraction solvent and the solvent demulsification technique to break up the emulsion simplified the procedure and facilitated its automation. Orthogonal array design (OAD) as an efficient optimization strategy was employed to optimize the extraction parameters, with all the experiments conducted auotmatically. An OA16 (41 × 212) matrix was initially employed for the identification of optimized extraction parameters (type and volume of extraction solvent, type and volume of dispersive solvent and demulsification solvent, demulsification time, and injection speed). Then, on the basis of the results, more levels (values) of five extraction parameters were investigated by an OA16 (45) matrix and quantitatively assessed by the analysis of variance (ANOVA). Enrichment factors of between 178- and 272-fold were obtained for the phthalate esters. The linearities were in the range of 0.1 and 50 μg/L and 0.2 and 50 μg/L, depending on the analytes. Good limits of detection (in the range of 0.01 to 0.02 μg/L) and satisfactory repeatability (relative standard deviations of below 5.9%) were obtained. The proposed method demonstrates for the first time integrated sample preparation by DLLME and analysis by GC/MS that can be operated automatically across multiple experiments.
Co-reporter:Sheng Tang, Guo Hui Chia, Yuepeng Chang, and Hian Kee Lee
Analytical Chemistry 2014 Volume 86(Issue 22) pp:11070
Publication Date(Web):October 16, 2014
DOI:10.1021/ac503323e
Automation of dispersive solid-phase extraction (d-SPE) presents significant challenges. Separation of the sorbent from the spent sample cannot be conducted without manual operations, including centrifugation, a widely used means of isolating a solid material from solution. In this work, we report an approach to d-SPE using dissolvable magnetic Fe3O4-layered double hydroxide core–shell microspheres as sorbent to enable automation of the integrative extraction and analytical processes. Through magnetic force, the sorbent, after extraction, was isolated from the sample and then dissolved by acid to release the analytes. Thus the customary analyte elution step in conventional SPE was unnecessary. The automated d-SPE step was coupled to high-performance liquid chromatography (HPLC) with photodiode array detection for determination of several pharmaceuticals and personal care products (PPCPs) [acetylsalicylic acid (ASA), 2,5-dihydroxybenzoic acid (DBA), 2-phenylphenol (PP), and fenoprofen (FP)] in aqueous samples. For the automated d-SPE process, experimental parameters such as agitation speed, temperature, time, and pH were optimized. The results showed that this method provided low limits of detection (between 0.021 and 0.042 μg/L), good linearity (r2 ≥ 0.9956), and good repeatability of extractions (relative standard deviations ≤4.1%, n = 6). The optimized procedure was then applied to determination of PPCPs in a sewage sample and ASA and FP in drug preparations. This fully automated extraction–HPLC approach was demonstrated to be an efficient procedure for extraction and analysis of ASA, DBA, PP, and FP in these samples.
Co-reporter:Seyed Mohammad Majedi, Barry C. Kelly, Hian Kee Lee
Analytica Chimica Acta 2014 Volume 814() pp:39-48
Publication Date(Web):3 March 2014
DOI:10.1016/j.aca.2014.01.022
•The robustness of cloud point extraction approach was investigated for the analysis of trace CuO NPs in water.•The behavior and fate, and therefore, the recovery of CuO NPs varied substantially under different extraction conditions.•The effects of environmental factors on the NP behavior and extraction were determined and minimized.•Limits of detection of 0.02 and 0.06 μg L−1 were achieved using ICP-MS and GF-AAS, respectively.•Environmental water samples were successfully pre-treated and analyzed.The cloud point extraction (CPE) of commercial copper(II) oxide nanoparticles (CuO NPs, mean diameter of 28 nm) in water samples was fully investigated. Factors such as Triton X-114 (TX-114) concentration, pH, incubation temperature and time, were optimized. The effects of CuO NP behavior like agglomeration, dissolution, and surface adsorption of natural organic matter, Cu2+, and coating chemicals, on its recovery were studied. The results indicated that all the CPE factors had significant effects on the extraction efficiency. An enrichment factor of ∼89 was obtained under optimum CPE conditions. The hydrodynamic diameter of CuO NPs increased to 4–5 μm upon agglomeration of NP-micelle assemblies, and decreased at pH >10.0 at which the extraction efficiency was also lowered. The solubility and therefore, the loss of NPs were greatly enhanced at pH <8.5 and in the first 60 min of incubation, whereas it declined at elevated incubation temperatures. Our results showed that the dissolved organic carbon (DOC) >5 mg C L−1 and Cu2+ >2 times that of CuO NPs, lowered and enhanced the extraction efficiency, respectively. Pre-treatment of samples with 3% w v−1 of hydrogen peroxide and 10 mM of ethylenediaminetetraacetic acid minimized the interferences posed by DOC and Cu2+, respectively. The decrease in CPE efficiency was also evident for ligands like poly(ethylene glycol). The TX-114-rich phase could be determined with either inductively coupled plasma mass spectrometry following microwave digestion, or graphite furnace atomic absorption spectrometry. The detection limits for CuO NPs were 0.02 and 0.06 μg L−1 using these techniques, respectively. The optimum sample pre-treatment and CPE conditions were successfully applied to the river and wastewater samples. The relative recoveries of CuO NPs spiked at 5–100 μg L−1 (as Cu) in these samples were in the range of between 59.2 and 108.2%. The approach demonstrates a robust analytical method for detecting trace levels of CuO NPs at their original states and assessing their exposure risks in real aquatic environments.
Co-reporter:Sheng Tang, Xuan Hao Lin, Sam Fong Yau Li, Hian Kee Lee
Journal of Chromatography A 2014 Volume 1373() pp:31-39
Publication Date(Web):19 December 2014
DOI:10.1016/j.chroma.2014.11.031
•An in-syringe dispersive solid-phase extraction approach was developed.•Layered double oxide hollow spheres were employed as a dissolvable sorbent.•The sorbent showed much high extraction efficiency due to high specific surface area.•Eleven US EPA listed phenols from aqueous samples were determined.Layered double oxide hollow spheres (LDO-HSs) were synthesized and employed as a dissolvable sorbent in dispersive solid-phase extraction (DSPE) to extract eleven United States Environmental Protection Agency's priority phenols from aqueous samples. With their higher specific surface area, LDO-HSs showed much higher extraction efficiency than normal layered double hydroxides and layered double oxides. The entire extraction process was accomplished in a syringe. After DSPE, the sorbent with the analytes was isolated conveniently by directly expelling the spent sample solution out of the syringe. The analyte-enriched sorbent was then subsequently dissolved by withdrawing an acidic solution into the syringe. The final extract was analyzed by high-performance liquid chromatography with ultraviolet detection. The results showed that this method provided low limits of detection for the phenols (0.005–0.153 μg/L), good linearity (r2 ≥ 0.9956) and relative standard deviations of ≤6.7%. The optimized method was applied to water samples from 3 rivers. This simple extraction procedure was demonstrated to be a fast, efficient and convenient DSPE approach.
Co-reporter:Maryam Lashgari, Hian Kee Lee
Journal of Chromatography A 2014 Volume 1369() pp:26-32
Publication Date(Web):21 November 2014
DOI:10.1016/j.chroma.2014.09.082
•Ten PFCAs were determined simultaneously using μ-SPE in fish fillet.•The effect of the matrix on MS signals was evaluated.•Surfactant-incorporated ordered mesoporous silica was applied as sorbent.•Recoveries ranged from 77% to 120%, and were independent of concentration.In the current study, a simple, fast and efficient combination of protein precipitation and micro-solid phase extraction (μ-SPE) followed by liquid chromatography–triple quadrupole tandem mass spectrometry (LC–MS/MS) was developed for the determination of perfluorinated carboxylic acids (PFCAs) in fish fillet. Ten PFCAs with different hydrocarbon chain lengths (C5–C14) were analysed simultaneously using this method. Protein precipitation by acetonitrile and μ-SPE by surfactant-incorporated ordered mesoporous silica were applied to the extraction and concentration of the PFCAs as well as for removal of interferences. Determination of the PFCAs was carried out by LC–MS/MS in negative electrospray ionization mode. MS/MS parameters were optimized for multiple reaction monitoring of the analytes. 13C mass labelled PFOA as a stable-isotopic internal standard, was used for calibration. The detection limits of the method ranged from 0.97 ng/g to 2.7 ng/g, with a relative standard deviation of between 5.4 and 13.5. The recoveries were evaluated for each analyte and were ranged from 77% to 120%. The t-test at 95% confidence level showed that for all the analytes, the relative recoveries did not depend on their concentrations in the explored concentration range. The effect of the matrix on MS signals (suppression or enhancement) was also evaluated. Contamination at low levels was detected for some analytes in the fish samples. The protective role of the polypropylene membrane used in μ-SPE in the elimination of matrix effects was evaluated by parallel experiments in classical dispersive solid phase extraction. The results evidently showed that the polypropylene membrane was significantly effective in reducing matrix effects.
Co-reporter:Hong Zhang, Benedict Wen Long Ng, Hian Kee Lee
Journal of Chromatography A 2014 Volume 1326() pp:20-28
Publication Date(Web):24 January 2014
DOI:10.1016/j.chroma.2013.12.056
•A novel, simple, fast and efficient LPME approach was developed. The plunger wire in a plunger-in-needle syringe was etched with hydrofluoric acid.•The acid-etched area served as LPME solvent holder.•The method exhibited enhanced extraction efficiency for PAHs.In this work, a novel, simple and fast one-step liquid-phase microextraction (LPME) approach, termed plunger-in-needle LPME was developed. In this method, the stainless steel plunger wire of a commercially available plunger-in-needle microsyringe was simply etched by immersion in hydrofluoric acid to form a microporous structure, and was used as the extractant solvent holder. The extractant solvent could be easily held within the pores created by the etching. When the plunger wire with the extractant solvent was exposed to the sample solution, analytes directly diffused from the sample solution to the solvent. After extraction, the plunger wire was directly introduced into the injection port of a gas chromatography–mass spectrometry (GC–MS) system for analysis of the analytes after thermal desorption. Polycyclic aromatic hydrocarbons (PAHs) were used as model analytes to evaluate the extraction performance of this new approach to LPME. Parameters affecting the extraction efficiency were investigated in detail. Under the optimized conditions, the method detection limits for 10 PAHs were in the range of 0.003 and 0.136 μg/L (at a signal/noise ratio of 3), with relative standard deviations of between 2.9% and 9.6% on the same etched plunger wire. The linearities of the calibration plots were from 0.05 to 50 or from 1 to 50 μg/L, depending on the PAHs. When this method was applied for the spiked river water sample, the relative recoveries ranged from 70.1% to 106.4%. The proposed method integrates the extraction and extract introduction into one device, without extraneous sorbent needed, which makes the procedure fast and simple. It is also an environmentally friendly approach as the organic solvent consumed is almost negligible.
Co-reporter:Sharon Yong, Yizhao Chen, Tong Kooi Lee, Hian Kee Lee
Talanta 2014 Volume 126() pp:163-169
Publication Date(Web):1 August 2014
DOI:10.1016/j.talanta.2014.03.058
•Hollow fiber liquid-phase microextraction for total thyroxine in human serum.•Extracts had comparable cleanness with those obtained using solid-phase extraction.•Serum samples were spiked with 13C6- thyroxine and analyzed by LC–MS/MS.•Replicates of 6 gave RSD of <1.3%. The difference from the SPE method was <1.2%.•Two reference materials of human serum were analyzed with good precision and accuracy.Determination of total thyroxine in human serum using hollow fiber liquid-phase microextraction (HF-LPME) has been accomplished for the first time. HF-LPME serves as an inexpensive sample pretreatment and the cleanup method that is nearly solvent-free. Thyroxine was extracted through a water immiscible organic solvent immobilized in the wall pores of a polypropylene hollow fiber into 20 μl of an aqueous acceptor phase inside the lumen of the hollow fiber. This technique produced extracts that had comparable cleanness with those obtained using solid-phase extraction (SPE). Serum samples with endogenous thyroxine were spiked with isotopically-labeled thyroxine and analyzed by liquid chromatography–tandem mass spectrometry after HF-LPME extraction. Extraction parameters including the organic phase, acid/base concentration of acceptor phase, stirring speed and extraction time were optimized. The calibration range was found to be linear over 1–1000 ng/g with the limit of detection (LOD) of 0.3 ng/g. For quantification of total thyroxine in human serum, 6 subsamples were prepared and the results indicated very good precision with a relative standard deviation of <1.3%. The difference from the SPE method was less than 1.2%, with independent t-test showing insignificant bias. Two reference materials of human serum were analyzed, and our obtained values were compared with the reference values. The results showed very good precision with RSD around 0.2% and the deviation from the reference values were −3.1% and −2.1%. The newly developed method is precise, accurate, inexpensive, and environmentally friendly.HF-LPME configurations. (A) 3 cm hollow fiber (straight) and (B) 7 cm hollow fiber (U-shape with extension).
Co-reporter:Ruyi Xu, Hian Kee Lee
Journal of Chromatography A 2014 1350() pp: 15-22
Publication Date(Web):
DOI:10.1016/j.chroma.2014.05.024
Co-reporter:Seyed Mohammad Majedi;Barry C. Kelly
Environmental Science and Pollution Research 2014 Volume 21( Issue 20) pp:11811-11822
Publication Date(Web):2014 October
DOI:10.1007/s11356-013-2381-7
Cloud point extraction (CPE) factors, namely Triton X-114 (TX-114) concentration, pH, ionic strength, incubation time, and temperature, were optimized for the separation of nano-sized copper(II) oxide (nCuO) in aqueous matrices. The kinetics of phase transfer was studied using UV–visible spectroscopy. From the highest separation rate, the most favorable conditions were observed with 0.2 % w/v of TX-114, pH = 9.0, ionic strength of 10 mM NaCl, and incubation at 40 °C for 60 min, yielding an extraction efficiency of 89.2 ± 3.9 % and a preconcentration factor of 86. The aggregate size distribution confirmed the formation of very large nCuO–micelle assemblies (11.9 μm) under these conditions. The surface charge of nCuO was also diminished effectively. An extraction efficiency of 91 % was achieved with a mixture of TX-100 and TX-114 containing 30 wt.% of TX-100. Natural organic and particulate matters, represented by humic acid (30 mg/L) and micron-sized silica particles (50 mg/L), respectively, did not significantly reduce the CPE efficiency (<10 %). The recovery of copper(II) ions (20 mg/L) in the presence of humic acid was low (3–10 %). The spiked natural water samples were analyzed either directly or after CPE by inductively coupled plasma mass spectrometry following acid digestion/microwave irradiation. The results indicated the influence of matrix effects and their reduction by CPE. A delay between spiking nCuO and CPE may also influence the recovery of nCuO due to aggregation and dissolution. A detection limit of 0.04 μg Cu/L was achieved for nCuO.
Co-reporter:Sheng Tang and Hian Kee Lee
Analytical Chemistry 2013 Volume 85(Issue 15) pp:7426
Publication Date(Web):July 16, 2013
DOI:10.1021/ac4013573
Three types of magnesium–aluminum layered double hydroxides were synthesized and employed as solid-phase extraction (SPE) sorbents to extract several aromatic acids (protocatechuic acid, mandelic acid, phthalic acid, benzoic acid, and salicylic acid) from aqueous samples. An interesting feature of these sorbents is that they dissolve when the pH of the solution is lower than 4. Thus, the analyte elution step, as needed in conventional sorbent-based extraction, was obviated by dissolving the sorbent in acid after extraction and separation from the sample solution. The extract was then directly injected into a high-performance liquid chromatography-ultraviolet detection system for analysis. In the key adsorption process, both dispersive SPE and co-precipitation extraction with the sorbents were conducted and experimental parameters such as pH, temperature, and extraction time were optimized. The results showed that both extraction methods provided low limits of detection (0.03–1.47 μg/L) and good linearity (r2 > 0.9903). The optimized extraction conditions were applied to human urine and sports drink samples. This new and interesting extraction approach was demonstrated to be a fast and efficient procedure for the extraction of organic anions from aqueous samples.
Co-reporter:Seyed Mohammad Majedi, Barry C. Kelly, Hian Kee Lee
Analytica Chimica Acta 2013 Volume 789() pp:47-57
Publication Date(Web):30 July 2013
DOI:10.1016/j.aca.2013.06.011
•We investigated an efficient microextraction technique for the analysis of Ag and TiO2 NPs in water.•NPs were surface-modified, and then quantitatively extracted and enriched into a solvent.•The most favorable reagents were optimized under environmentally relevant conditions.•Limits of detection of 0.02 and 0.07 μg L−1 were achieved for Ag and TiO2 NPs, respectively.•Natural water samples were successfully analyzed and characterized.Hydrophobic silver and titanium (IV) oxide nanoparticles (commercial Ag and TiO2 NPs with average particle sizes of 17 and 19 nm, respectively) were quantitatively transferred into organic phase in natural water samples. Five NP surface modification and solvent extraction agents (reagents) types, mercaptocarboxylic acid, alkylamine, mediator solvent, extraction solvent, and surfactant, were investigated and optimized with three-level orthogonal array design (OAD), an OA27 (313) matrix. The most favorable reagents and experimental conditions were then examined. The best extraction efficiencies of 78.6 and 73.7% were obtained for 1 mg L−1 citrate-stabilized Ag and TiO2 NPs, respectively, with 0.5 mM of 11-mercaptoundecanoic acid, 1.5 mM of octadecylamine, 1 mL of methanol, 150 μL of cyclohexane, 0.05 mM of tetra-n-octylammonium bromide, pH = 8.0, adsorption time of 2 h, sonication time of 3 min, and centrifugation time of 10 min. Enrichment factors were 97 and 83, for Ag and TiO2 NPs, respectively. The optimum extraction conditions were successfully applied to genuine water samples at spiking levels of 2–100 μg L−1 of Ag and TiO2 NPs. The relative recoveries of (69.0–85.1)% and (61.5–78.5)% were obtained for Ag and TiO2 NPs, respectively. The extracted surface-modified NPs were characterized with transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray, ultraviolet–visible, and Fourier transform infrared spectroscopic techniques. Based on the results, efficient ligand exchange and acid–base pair formation were observed on the NP surface without significant change in its original properties. The organic phase was microwave digested, and analyzed with inductively coupled plasma (ICP) optical emission spectroscopy and ICP mass spectrometry (ICP-MS). Detection limits of ICP-MS analyses of Ag and TiO2 NPs were 0.02 and 0.07 μg L−1, respectively.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1286() pp:9-15
Publication Date(Web):19 April 2013
DOI:10.1016/j.chroma.2013.02.067
For the first time, a novel one-step sample preparation method that combines microwave assisted extraction and solvent bar microextraction (MAE–SBME) with analysis by gas chromatography–mass spectrometry (GC–MS), was developed for the fast and efficient determination of polycyclic aromatic hydrocarbons (PAHs) in environmental soil samples. An interesting feature of the new procedure is that SBME was conducted simultaneously with MAE. Thus, the extract from the SBME could be directly and immediately analyzed by GC–MS. A separate clean up and/or preconcentration process, such as time-consuming and tedious gel permeation chromatography, solid-phase extraction, filtration, or adsorption chromatography, normally associated with conventional MAE, was not necessary. It is also notable that the procedure was environmentally benign since water was used as the extraction solvent in MAE, and only several microliters of organic solvent were used in SBME. Some factors affecting the extraction were studied and optimized. Under the most favorable conditions, the method showed good linearities (between 0.2 and 500, 0.5 and 500, 1 and 500, and 2 and 500 ng/g, depending on the analytes), low limits of detection (from 0.03 to 0.25 ng/g), and satisfactory precision (with relative standard deviations below 9.8%). The MAE–SBME procedure provides a fast and simple sample preparation approach for the processing of environmental soil samples.Highlights► Microwave assisted extraction (MAE) combined with solvent bar microextraction (SBME) in one step. ► Analyte clean-up by SBME was conducted simultaneously with MAE, avoiding separate clean-up step. ► The combined approach was solvent-minimized, efficient and fast, and gave low LODs, good linearity and repeatability.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1274() pp:28-35
Publication Date(Web):25 January 2013
DOI:10.1016/j.chroma.2012.12.017
For the first time, a novel low-density solvent-based vortex-assisted surfactant-enhanced-emulsification liquid–liquid microextraction (LDS–VSLLME) was developed for the fast, simple and efficient determination of six phthalate esters (PEs) in bottled water samples followed by gas chromatography–mass spectrometry (GC–MS). In the extraction procedure, the aqueous sample solution was injected into a mixture of extraction solvent (toluene) and surfactant (cetyltrimethyl ammonium bromide), which were placed in a glass tube with conical bottom, to form an emulsion by the assistance of vortex agitation. After extraction and phase separation by centrifugation, and removal of the spent sample, the toluene extract was collected and analyzed by GC–MS. The addition of surfactant enhanced the dispersion of extraction solvent in aqueous sample and was also favorable for the mass transfer of the analytes from the aqueous sample to the extraction solvent. Moreover, using a relatively less toxic surfactant as the emulsifier agent overcame the disadvantages of traditional organic dispersive solvents that are usually highly toxic and expensive and might conceivably decrease extraction efficiency to some extent since they are not as effective as surfactants themselves in generating an emulsion. With the aid of surfactant and vortex agitation to achieve good organic extraction solvent dispersion, extraction equilibrium was achieved within 1 min, indicating it was a fast sample preparation technique. Another prominent feature of the method was the simple procedure to collect a less dense than water solvent by a microsyringe. After extraction and phase separation, the aqueous sample was removed using a 5-mL syringe, thus leaving behind the extract, which was retrieved easily. This novel method simplifies the use of low-density solvents in DLLME. Under the optimized conditions, the proposed method provided good linearity in the range of 0.05–25 μg/L, low limits of detection (8–25 ng/L) and good enrichment factors up to 290. The proposed method was successfully applied to the extraction of PEs in bottled water samples as a fast, efficient, and convenient method.Highlights► LDS–VSLLME–GC–MS was applied to the determination of PEs. ► Low density and less toxic organic solvent toluene was used as extractant. ► Good extraction solvent dispersion was achieved by relatively less toxic surfactant combined with vortex agitation. ► Fast extraction time (within 1 min) and high extraction efficiency with good enrichment factors up to 290 were achieved. ► The low-density organic solvent collection procedure was simple and fast.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1317() pp:217-222
Publication Date(Web):22 November 2013
DOI:10.1016/j.chroma.2013.04.014
•A novel and fast preconcentration approach, IL-DLLME-VA-μ-SPE was developed for antidepressant drugs in water.•The μ-SPE step was preceded by fast sonication-assisted DLLME.•Simple and efficient method with low LODs, good linearity and repeatability.Ionic liquid-dispersive liquid–liquid microextraction combined with micro-solid phase extraction (IL-DLLME-μ-SPE), and high-performance liquid chromatography (HPLC) was developed for the determination of tricyclic antidepressants (TCAs) in water samples. Two hundred microliters of an organic solvent (as disperser solvent) and 20 μl of 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate were injected into a 5.0 ml sample for sonication-assisted DLLME. After this, a μ-SPE device, containing a novel material zeolite imidazolate framework 4 (ZIF-4), was added into the sample solution and 1 min of vortex-assisted extraction was performed. After 5 min of sonication-assisted desorption, 10 μl of desorption solvent was injected into a HPLC system for analysis. A characteristic property of DLLME-VA-μ-SPE is that any organic solvent and solid sorbent immiscible with water can be used. Special apparatus, or conical-bottom test tubes, and tedious procedures conventionally associated with DLLME such as centrifugation, or refrigeration of solvent are not necessary in the present approach. A novel material, ZIF-4 was employed as μ-SPE sorbent. Under the optimized conditions, the calibration curves were linear in the range of 1–1000 μg/L. The relative standard deviations and the limits of detection were in the range of 1.5% and 7.8% and 0.3 and 1 μg/L, respectively. The relative recoveries of canal water samples, spiked with drugs, were in the range of 94.3% and 114.7%. The results showed that IL-DLLME-μ-SPE was suitable for the determination of TCAs in water samples.
Co-reporter:Tze Han Lim, Lingna Hu, Cong Yang, Chaobin He, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1316() pp:8-14
Publication Date(Web):5 November 2013
DOI:10.1016/j.chroma.2013.09.034
•μ-SPE of selected analgesics and psychiatric pharmaceuticals.•First reported use of urea-decorated silica gel sorbents for μ-SPE.•Enrichment factors comparable to those for μ-SPE using NH2 decorated silica gel sorbents.•Enrichment factors exceeded those of C18-silica gel sorbents.Individual polar sorbents with surface-displayed amino groups (APS) and non-nucleophilic urea-groups (UPS), were prepared by chemical modification of granular silica gel with bifunctional silane coupling reagents. In this preliminary study, they were separately employed for micro-solid phase extraction (μ-SPE) of the quarternary salt of Amitriptyline (Ami), Carbamazepine (Cbz), Ketoprofen (Ket) and Diclofenac (Dfn) from aqueous samples in conjunction with high performance liquid chromatography. The resulting enrichment factors for both APS and UPS are comparable and exceeded those of μ-SPE involving commercial C18-silica gel sorbents. The presence of highly polar, but non-basic and non-nucleophilic surfaces on UPS prompted the development of a UPS-based μ-SPE method. Good linear correlation was found over a concentration range of 0–50 μg L−1 with limits of detection ranging from 0.66 to 2.36 μg L−1). Limits of quantification between 1.61 and 7.88 μg L−1 were obtained. HPLC analyses indicated that relative recoveries of 123% for Ami, 65.6% for Cbz, 71.2% for Ket and 66.5% for Dfn were obtained during μ-SPE of spiked (10 μg L−1) environmental water samples with percentage relative standard deviations (%RSD) of between 2.1% and 12.6%.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1271(Issue 1) pp:56-61
Publication Date(Web):4 January 2013
DOI:10.1016/j.chroma.2012.11.047
In the present study, a rapid, highly efficient and environmentally friendly sample preparation method named temperature-controlled ionic liquid dispersive liquid-phase microextraction (TC-IL-DLPME), followed by high performance liquid chromatography (HPLC) was developed for the extraction, preconcentration and determination of four benzophenone-type ultraviolet (UV) filters (viz. benzophenone (BP), 2-hydroxy-4-methoxybenzophenone (BP-3), ethylhexyl salicylate (EHS) and homosalate (HMS)) from water samples. An ultra-hydrophobic ionic liquid (IL) 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM][FAP]), was used as the extraction solvent in TC-IL-DLPME. Temperature served two functions here, the promotion of the dispersal of the IL to the aqueous sample solution to form infinitesimal IL drops and increase the interface between them and the target analytes (at high temperature), and the facilitation of mass transfer between the phases, and achievement of phase separation (at low temperature). Due to the ultra-hydrophobic feature and high density of the extraction solvent, complete phase separation could be effected by centrifugation. Moreover, no disperser solvent was required. Another prominent feature of the procedure was the combination of extraction and centrifugation in a single step, which not only greatly reduced the total analysis time for TC-IL-DLPME but also simplified the sample preparation procedure. Various parameters that affected the extraction efficiency (such as type and volume of extraction solvent, temperature, salt addition, extraction time and pH) were evaluated. Under optimal conditions, the proposed method provided good enrichment factors in the range of 240–350, and relative standard deviations (n = 5) below 6.3%. The limits of detection were in the range of 0.2–5.0 ng/mL, depending on the analytes. The linearities were between 1 and 500 ng/mL for BP, 5 and 1000 ng/mL for BP-3, 10 and 1000 ng/mL for HMS and 5 and 1000 ng/mL for EHS. Finally, the proposed method was successfully applied to the determination of UV filters in swimming pool and tap water samples and acceptable relative recoveries over the range of 88.0–116.0% were obtained.Highlights► TC-IL-DLPME-HPLC-UV was for the first time applied to the determination of UV filters. ► High extraction efficiency with good enrichment factors of up to 350 were achieved. ► The new method did not need a disperser solvent. ► Extraction and centrifugation were combined into a single step. ► Simple and efficient method with low LODs, good repeatability and linearity.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1273() pp:12-17
Publication Date(Web):18 January 2013
DOI:10.1016/j.chroma.2012.11.084
In this paper, a novel liquid phase microextraction (LPME) approach was developed in which a piece of knitting wool was used as the extractant solvent holder. Owing to the absorbability of the wool, the extractant could be easily held within the material. When the wool containing the organic solvent was exposed to the sample solution, analytes could directly diffuse from the sample solution to the solvent. Ultraviolet (UV) filters ([2,4-dihydroxybenzophenone (BP-1), benzophenone (BP) and 2-hydroxy-4-methoxybenzophenone (BP-3)]) were used as model analytes to evaluate the procedure. Parameters that affect the extraction efficiency (selection of organic solvent, volume of the extractant, agitation speed, extraction time, salt concentration and pH) were investigated. The proposed method in combination with liquid chromatography-UV detection, provided good enrichment factors up to 366, with relative standard deviations of between 0.6% and 4.2% on the same piece of wool, and good linearity from 0.1 ng/ml to 100 ng/ml for all the analytes with regression coefficients of between 0.9998 and 0.9999. The limits of quantification of these compounds, calculated at S/N = 10, were 0.1 ng/ml, 0.07 ng/ml and 0.1 ng/ml for BP-1, BP, BP-3, respectively. The method was applied to the determination of BP-type UV filters in swimming pool water. This is the first report of an application of knitting wool as a solvent holder for LPME. The procedure is cost-effective, and easy to operate.Highlights► A novel LPME procedure using knitting wool as solvent holder. ► High extraction efficiency with good enrichment factors up to 366 were achieved. ► The new method can sustain high agitation speed and long extraction time. ► Simple and cost-effective method with low LODs, good repeatability and linearity.
Co-reporter:Tsze Yin Tan, Chanbasha Basheer, Melgious Jin Yan Ang, Hian Kee Lee
Journal of Chromatography A 2013 Volume 1297() pp:12-16
Publication Date(Web):5 July 2013
DOI:10.1016/j.chroma.2013.04.082
•Electroenhanced solid-phase microextraction of methamphetamine with commercial fibers.•The method is simple, fast, has satisfactory precision and accuracy.•Application of developed procedure for the analysis of human urine samples.Electroenhanced solid-phase microextraction (EE-SPME) method with gas chromatographic mass spectrometric analysis was investigated for the determination of methamphetamine in urine sample with commercial fibers. In this approach, commercial SPME fibers were used in direct immersion mode with an applied potential to extract methamphetamine. EE-SPME was more effective in the extraction compared to conventional SPME (i.e. application of potential). The method was simple to use, and avoided the need for alkalization and derivatization of methamphetamine. Experimental conditions were optimized to achieve better extraction performance. Various conditions including applied potential, sample pH, extraction and desorption time were investigated. Based on the optimized conditions, EE-SPME achieved a higher enrichment factor of 159-fold than conventional SPME. The calibration plot under the best selected parameters was linear in the range of 0.5–15 ng/mL (r = 0.9948). The feasibility of EE-SPME was demonstrated by applying it to the analysis of human urine samples. The limit of detection of methamphetamine was 0.25 ng/mL with a satisfactory relative standard deviation of 6.12% (n = 3) in human urine.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2013 1300() pp: 24-30
Publication Date(Web):
DOI:10.1016/j.chroma.2013.01.030
Co-reporter:Seyed Mohammad Majedi, Hian Kee Lee, and Barry C. Kelly
Analytical Chemistry 2012 Volume 84(Issue 15) pp:6546
Publication Date(Web):June 27, 2012
DOI:10.1021/ac300833t
Cloud point extraction (CPE) with inductively coupled plasma mass spectrometry (ICPMS) was applied to the analysis of zinc oxide nanoparticles (ZnO NPs, mean diameter ∼40 nm) in water and wastewater samples. Five CPE factors, surfactant (Triton X-114 (TX-114)) concentration, pH, ionic strength, incubation temperature, and incubation time, were investigated and optimized by orthogonal array design (OAD). A three-level OAD, OA27 (313) matrix was employed in which the effects of the factors and their contributions to the extraction efficiency were quantitatively assessed by the analysis of variance (ANOVA). Based on the analysis, the best extraction efficiency (87.3%) was obtained at 0.25% (w/v) of TX-114, pH = 10, salt content of 15 mM NaCl, incubation temperature of 45 °C, and incubation time of 30 min. The results showed that surfactant concentration, pH, incubation time, and ionic strength exert significant effects on the extraction efficiency. Preconcentration factors of 62 and 220 were obtained with 0.25 and 0.05% (w/v) TX-114, respectively. The relative recoveries of ZnO NPs from different environmental waters were in the range 64–123% at 0.5–100 μg/L spiked levels. The ZnO NPs extracted into the TX-114-rich phase were characterized by transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDS) and UV–visible spectrometry. Based on the results, no significant changes in size and shape of NPs were observed compared to those in the water before extraction. The extracted ZnO NPs were determined after microwave digestion by ICPMS. A detection limit of 0.05 μg/L was achieved for ZnO NPs. The optimized conditions were successfully applied to the analysis of ZnO NPs in water samples.
Co-reporter:Tsze Yin Tan, Chanbasha Basheer, Kai Perng Ng, Hian Kee Lee
Analytica Chimica Acta 2012 Volume 739() pp:31-36
Publication Date(Web):20 August 2012
DOI:10.1016/j.aca.2012.06.007
A simple and sensitive single step electro membrane extraction (EME) procedure was demonstrated for biological organic anions with determination by ion chromatography (IC). Nitrite, adipate, oxalate, iodide, fumarate, thiocyanate and perchlorate were extracted from aqueous donor solutions, across a supported liquid membrane (SLM) consisting of methanol impregnated in the walls of a porous polypropylene membrane bag and into an alkaline aqueous acceptor solution in the lumen of the propylene envelope by the application of potential of 12 V applied across the SLM. The acceptor solution was analyzed by IC. Parameters affecting the extraction performance such as type of SLM, extraction time, pH of the donor and acceptor solution, and extraction voltage were studied. The most favorable EME conditions were methanol as the SLM, extraction time of 5 min, pH of acceptor and sample solutions of 12 and 4, respectively, and a voltage of 12 V. Portable 12 V batteries were used in the study. Under these optimized conditions, all anions had enrichment factors ranging from 3.6 to 36.2 with relative standard deviations (n = 3) of between 6.6 and 17.5%. Good linearity ranging from 0.1 to 10 μg mL−1 with coefficients of correlation (r) of between 0.9981 and 0.9996 were obtained. The limits of detection of the EME-IC method were from 0.01 to 0.14 μg mL−1. The developed methodology was applied to amniotic fluid samples to evaluate the feasibility of the method for real applications.Graphical abstract. Schematic of (a) battery-operated electro membrane extraction, (b) proposed extraction mechanism and (c) selected target anions.Highlights► One-step battery-operated electro membrane extraction of anions from biological samples. ► Extraction performance was compared with liquid-phase microextraction. ► Simple and efficient analytical approach with low LODs, good linearity and repeatability.
Co-reporter:Hong Zhang, Hian Kee Lee
Analytica Chimica Acta 2012 Volume 742() pp:67-73
Publication Date(Web):12 September 2012
DOI:10.1016/j.aca.2012.03.016
A simple, sensitive and selective method for the simultaneous determination of five ultraviolet (UV) filters: benzophenone, octyl salicylate, homosalate, 3-(4-methylbenzylidene) camphor, 2-hydroxy-4-methoxybenzophenone in aqueous samples was developed. The analytes were extracted by plunger-in-needle solid-phase microextraction with graphene as sorbent, then silylated on-fiber with N-methyl-N-(trimethylsilyl)trifluoroacetamide, and analyzed by gas chromatography–mass spectrometry. Factors affecting the performance of extraction and derivatization steps were thoroughly evaluated. For the optimization of extraction conditions, six relevant factors (parameters) were investigated, including sample pH, salt concentration, extraction time, extraction temperature, stirring speed and sampling mode. In the first stage, a two-level orthogonal array design OA8 (27) matrix was employed to study the effect of six factors. Based on the results of the first stage, three factors were selected for further optimization with a univariant approach during the second stage. Under the final optimized conditions, the method limits of detection for the five UV filters were determined to be in the range of 0.5 and 6.8 ng L−1 (at a signal/noise ratio of 3) and the precision (% relative standard deviation, n = 5) was 0.8–5.6% at a concentration level of 1 μg L−1. The linearities for different analytes were 10–10,000 or 1–5000 ng L−1. The coefficients of determination for the calibration curves were all greater than 0.994. Finally, the proposed method was successfully applied to the extraction and determination of the UV filters in river water samples.Graphical abstractCompared with commercial SPME fibers, the sol–gel graphene coating exhibited different selectivity for five UV filters with the log P values in the range of 3.18 and 5.95. Extraction conditions: each UV filter at 10 μg L−1 concentration in aqueous sample, pH = 5, 40-min extraction time, room temperature, direct sampling 0% NaCI, 1000 rpm, n = 3.Highlights► Five UV filters are simultaneously determined by plunger-in-needle SPME-GC–MS. ► Novel sol–gel graphene is used as sorbent. ► OAD is employed to optimize extraction parameters.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1251() pp:27-32
Publication Date(Web):17 August 2012
DOI:10.1016/j.chroma.2012.06.048
A novel microextraction approach termed ionic liquid based ultrasound-assisted emulsification microextraction (IL-USAEME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) was developed for the preconcentration and detection of organic ultraviolet (UV) filters in environmental water samples. An ionic liquid (IL) was used in place of an organic solvent as in conventional USAEME. In the study, orthogonal array designs (OAD) were employed for the optimization of the extraction parameters: type of IL, pH of the sample, extraction volume, ultrasonic time and salt concentration. In the first step, a mixed level OAD matrix, OA16 (41 × 212) was employed for the initial optimization. Based on the results of the first step, an ultra-hydrophobic IL, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate was chosen as the IL extractant and sample pH was set at a value of 3. Ultrasonic time, extraction volume and salt concentration were further optimized in the second step by an OA16 (45) matrix. Under the latter optimized conditions, calibration curves with coefficients of estimation higher than 0.997 over the concentration range of 5 and 1000 ng/ml, and the relative standard deviations for six replicates of the extraction from 2.6 to 6.6% were obtained. The limits of detection for four organic UV filters were between 0.5 and 1 ng/ml. The validated technique was applied to the analysis of organic UV filters in environmental water samples.Highlights► Ionic liquid, [HMIM][FAP], was used as a novel extractant in USAEME. ► Orthogonal array designs were employed for optimization of extraction parameters. ► Simple, fast and efficient method with good linearity, low LODs and %RSDs.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1249() pp:25-31
Publication Date(Web):3 August 2012
DOI:10.1016/j.chroma.2012.06.019
For the first time, a simple solvent microextraction method termed vortex-assisted liquid–liquid microextraction (VADLLME) coupled with gas chromatography–mass spectrometry (GC–MS) has been developed and used for the analysis of six benzophenone ultraviolet (UV) filters (i.e. benzhydrol, 2,4-dihydroxybenzophenone, benzophenone, 2-hydroxy-4-methoxybenzophenone, ethylhexyl salicylate and homosalate) in water samples. The most favorable extraction variables in the VADLLME process were determined. In the extraction procedure, 40 μL of tetrachloroethene as extraction solvent were directly injected into a 15-mL centrifuge tube containing 10 mL of aqueous sample, adjusted to pH 4 for VADLLME. After VADLLME, the extract was evaporated under a gentle nitrogen gas stream and then reconstituted with N,O-bis-(trimethylsilyl)trifluoroacetamide (BSTFA), thus allowing the target analytes to be converted into their trimethylsilyl derivatives to optimize the GC–MS analysis. No centrifugation and disperser solvent were required in this microextraction procedure. Significantly, short extraction time and high extraction efficiency were achieved. This method opens up a potentially new horizon for on-site dispersive liquid–liquid microextraction. Under the optimum conditions, the proposed method provided good enrichment factors up to 310, with relative standard deviations ranging from 6.1 to 12.9%. The limits of quantification were in the range of 20–100 ng/L, depending on the analytes. The linearities were between 0.05 and 10 μg/L and 0.1 and 10 μg/L for different UV filters. Finally, the proposed method was successfully applied to the determination of UV filters from spiked genuine water samples and acceptable recoveries over the range of 71.0–120.0% were obtained.Highlights► VADLLME-GC–MS was for the first time applied to the determination of UV filters. ► High extraction efficiency with good enrichment factors up to 310 were achieved. ► The new method did not need centrifugation or disperser solvent. ► Fast extraction time relative to other methods was another advantage. ► Simple and efficient method with low LODs, good repeatability and linearity.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1229() pp:1-5
Publication Date(Web):16 March 2012
DOI:10.1016/j.chroma.2011.12.110
Hollow fiber protected liquid phase microextraction using an ionic liquid as supported phase and acceptor phase (IL-HF-LPME) is proposed for the determination of four ultraviolet (UV) filters (benzophenone, 3-(4-methylbenzylidene)-camphor, 2-hydroxy-4-methoxybenzophenone and 2,4-dihydroxybenzophenone) in water samples for the first time. In the present study, four different ILs 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate) [HMIM][FAP], 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate [BMPL][FAP], 1-butyl-3-methylimidazolium phosphate ([BMIM][PO4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were evaluated as extraction solvent. Only [HMIM][FAP] showed high chemical affinity to the analytes which permits a selective isolation of the UV filters from the sample matrix, allowing also their preconcentration. IL-HF-LPME and high performance liquid chromatography provides repeatability from 1.1% to 8.2% and limits of detection between 0.3 and 0.5 ng/ml. Real water samples spiked with the analytes extracted were analyzed, and yielded relative recoveries ranging from 82.6% to 105.9%.Highlights► Ionic liquid [HMIM][FAP] was employed as supported phase and acceptor phase in HF-LPME. ► [HMIM][FAP] shows high extraction efficiency for UV filter extraction from aqueous samples. ► Simple and efficient method with low LODs, good linearity and repeatability.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1263() pp:1-6
Publication Date(Web):9 November 2012
DOI:10.1016/j.chroma.2012.09.016
Mixed zeolitic imidazolate framework 8 (ZIF-8) (nanometer and micron-sized) material were synthesized and applied as sorbent to sonication-assisted emulsification microextraction coupled to vortex-assisted porous membrane-protected micro-solid-phase extraction (SAE-VA-μ-SPE) of polycyclic aromatic hydrocarbons (PAHs) from water samples. Better extraction results was obtained by using the mixed sorbent for the extraction of PAHs from aqueous samples, than either nanometer or micron-sized ZIF-8 separately. The developed method proved to be a time-saving, highly efficient (total extraction procedure was less than 10 min), accurate and robust method for water sample pretreatment. Parameters influencing the extraction efficiency such as desorption solvent, extraction solvent volume, emulsification time, desorption time and salt concentration were investigated and optimized. The limits of detection from gas chromatography–mass spectrometric analysis of six PAHs after SAE-VA-μ-SPE ranged between 0.004 and 0.011 ng/ml. The linear ranges were from 0.05 to 50 ng/ml, and the correlation coefficient was higher than 0.9943. The proposed method provides an interesting and innovative approach of combining different microscale sample preparation methods to solve analytical problems that are not easily addressed by the individual procedure alone.Highlights► Mixed ZIF-8 (nanometer and micron-sized) was used as extraction sorbent of vortex-assisted (VA) μ-SPE. ► The μ-SPE step was preceded by a fast sonication-assisted emulsification (SAE) microextraction. ► SAE-VA-μ-SPE showed good linearity, low LODs and %RSDs for the extraction of PAHs.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1257() pp:19-24
Publication Date(Web):28 September 2012
DOI:10.1016/j.chroma.2012.08.032
A novel and fast procedure, sonication-assisted emulsification microextraction combined with vortex-assisted porous membrane protected micro-solid-phase extraction (SAEME-VA-μ-SPE), was developed for the gas chromatography–mass spectrometric determination of acidic drugs from environmental water samples. One advantage of the new procedure is that any solvent immiscible with water can be used as extractant solvent of SAEME and any solid sorbent can be used for μ-SPE in the SAEME-VA-μ-SPE process. In the present work, zeolite imidazolate framework 8 (ZIF-8) was employed as extraction sorbent for μ-SPE and 1-octanol as extractant solvent for SAEME. ZIF-8 has very good thermal, chemical and water stability, which make it a suitable material for the extraction of trace analytes from aqueous samples. Under the optimized extraction conditions, the developed method exhibited low limits of detection (0.01–0.04 ng/ml), good linearity (with r2 between 0.9965 and 0.9993) from 0.5 to 50 ng/ml and satisfactory repeatability (between 4.1% and 7.6%). In essence SAEME-VA-μ-SPE is a combination of two different and efficient miniaturized techniques. It was demonstrated to be a fast, accurate, and convenient pretreatment procedure for trace analysis of environmental water samples.Highlights► A novel and fast preconcentration approach, SAEME-VA-μ-SPE was developed. ► Any extractant solvent immiscible with water, and any sorbent, can be used for SAEME-VA-μ-SPE. ► Simple, fast and efficient microextraction method with good linearity, low LODs and %RSDs.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1235() pp:1-9
Publication Date(Web):27 April 2012
DOI:10.1016/j.chroma.2012.02.045
A fast and efficient method for the determination of trace level of carbamate pesticides using a lower-density-than-water solvent for ultrasound-assisted emulsification microextraction coupled to on-column derivatization and analysis by GC–MS has been developed and studied. In this approach, a soft plastic Pasteur pipette was employed as a convenient extraction device. Fifty microliters of extraction solvent, of lower density than water, was injected into the sample solution held in the pipette. The latter was immediately immersed in an ultrasound water bath to form an emulsion. After 2 min extraction, the emulsion was fractionated into two layers by centrifugation. The upper layer (organic extract) could be collected conveniently by squeezing the bulb of the pipette, now held upside down, to move it into the narrow stem of the device, facilitating its retrieval for analysis. The extract was then combined with trimethylphenylammonium hydroxide and directly injected into a gas chromatography–mass spectrometry (GC–MS) system for on-column derivatization and analysis. The on-column derivatization provided an added convenience (since a separate step was not necessary). Parameters affecting the derivatization and extraction were investigated. Under the most favorable conditions, the method demonstrated high extraction efficiency with low limits of detection of between 0.01 and 0.1 μg/L, good linearity in the range of 0.05–50 μg/L, to 0.5–100 μg/L, and good repeatability (RSD below 9.2%, n = 5). The proposed method was evaluated by determining carbamate pesticides in river water samples.Highlights► Low-density solvent ultrasound emulsification microextraction with derivatization. ► Plastic pipette allows convenient use of lower-density-than-water solvents in DLLME. ► On-column derivatization avoids separate derivatization and expedites the procedure. ► Fast simple and efficient approach with low LODs, good linearity, and good repeatability.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1252() pp:67-73
Publication Date(Web):24 August 2012
DOI:10.1016/j.chroma.2012.06.065
In this study, a polyethylene Pasteur pipette-based ultrasound-assisted emulsification microextraction (USAEME) applying low-density organic solvent was successfully developed for the extraction of trace levels of organochlorine pesticides (OCPs) in water samples and followed by gas chromatography–mass spectrometry (GC–MS) analysis. In this approach, a polyethylene Pasteur squeeze-type pipette was employed as a convenient extraction device and ultrasound radiation was applied to accelerate the emulsification of low-density organic solvent in aqueous solutions to enhance the microextraction efficiency of OCPs in water samples. Thirty microliters of extraction solvent (isooctane), of lower density than water, were injected into the aqueous sample solution held in the pipette. The latter was then immersed in an ultrasound water bath to form an emulsion. After 30 s extraction, phase separation was achieved by centrifugation. The upper layer (isooctane) was collected and analyzed by GC–MS. No disperser solvent was required in this procedure. Significantly, fast analysis and high extraction efficiency were achieved. Another feature of the procedure was the use of the pipette as the extraction device, which permitted less dense than water organic solvent to be used as extraction solvent. This method broadens the applicability of USAEME to a wider range of solvent. Additionally, carry-over problems were avoided with the use of the disposable pipette. Parameters affecting the efficiency of polyethylene Pasteur pipette-based USAEME, such as the extraction solvent, extraction solvent volume, extraction and centrifugation time, ionic strength and extraction temperature were investigated. Under the optimum conditions, the proposed method provided good enrichment factors (EFs) in the range of 128 and 328, with relative standard deviations (RSDs) ranging from 2.7% to 12.4%. The limits of detection were in the range of 0.8 and 10 ng/L depending on the analytes. The linearities were between 0.01 and 50 μg/L for hexachlorobenzene, dieldrin, endrin and o,p′-DDD, 0.05–25 μg/L for heptachlor, and 0.005–50 μg/L for p,p′-DDE. Finally, the polyethylene Pasteur pipette-based USAEME was successfully used for the fast determination of OCPs in river and tap water samples. The proposed method provides a simple, convenient, rapid, sensitive, cost-effective, and environmentally friendly process for the determination of OCPs in water samples.Highlights► A low-density organic solvent-based USAEME with GC–MS was applied to the determination of OCPs. ► No disperser solvent was required, and high extraction efficiency was achieved. ► Fast extraction time relative to other methods was another advantage. ► Simple and efficient method with good LODs, good repeatability and linearity.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1243() pp:14-22
Publication Date(Web):22 June 2012
DOI:10.1016/j.chroma.2012.04.054
A highly efficient and simple two-step method, electro membrane extraction (EME) followed by low-density solvent based ultrasound-assisted emulsification microextraction (EME–LDS-USAEME) combined with derivatization and analysis by gas chromatography–mass spectrometry (GC–MS), was developed for the determination of trace level chlorophenols in environmental water samples. In the first step, the analytes were extracted, under electrical potential, from the sample solution into the acceptor solution, which was held in a polypropylene membrane sheet with 1-octanol as the supported liquid membrane. The acceptor solution from the first step was then employed as the sample solution for the second step of LDS-USAEME. In this step, the target analytes were extracted into a solvent with lower density than water that was dispersed in the sample solution with the assistance of ultrasound. The extract was separated from the sample solution by centrifugation and collected as the upper layer. Finally, the extract with a derivatization reagent were injected into a GC–MS system for analysis. Six chlorophenols, 2-chlorophenol, 4-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were selected here as model compounds for developing and evaluating the method. Several factors influencing the extraction and derivatization were investigated. With the EME–LDS-USAEME procedure, high enrichment factors of up to 2198 were achieved. Under the most favorable conditions, good limits of detection (down to 0.005 μg/L), linearity (from 0.05–10 to 0.2–10 μg/L, depending on the analytes), and repeatability of extraction (RSDs below 9.7%, n = 5) were obtained. The proposed method was applied to determine chlorophenols in drainwater samples.Highlights► Electro membrane extraction followed by ultrasound emulsification microextraction is reported. ► Flexible pipette allows convenient retrieval of lower density extract in USAEME. ► On-column derivatization avoids separate derivatization and expedites the procedure. ► High extraction efficiency for chlorophenols from aqueous samples obtained. ► The approach is fast and gives low LODs, good linearity and repeatability.
Co-reporter:Hong Zhang, Wei Ping Low, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1233() pp:16-21
Publication Date(Web):13 April 2012
DOI:10.1016/j.chroma.2012.02.020
This report describes the use of sulfonated graphene sheets as sorbent in micro-solid-phase extraction (μ-SPE), together with gas chromatography–mass spectrometry, for the determination of polycyclic aromatic hydrocarbons (PAHs) in water. In this study, for the first time, graphene sheets were used as a sorbent material for this mode of microextraction. The modified graphene sheets were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. μ-SPE parameters such as extraction time, desorption time and desorption solvent were optimized. The method showed good precision, reproducibility and linear response for PAH analysis over a concentration range of 0.05–100 μg/L for naphthalene and 0.01–100 μg/L for the remaining PAHs (acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) with coefficient of determination (r2) of higher than 0.992. Limits of detection of from 0.8 to 3.9 ng/L for 7 PAHs were achieved. The developed method was successfully applied to determine PAHs in river water samples.Highlights► Sulfonated graphene sheets are used as sorbent in μ-SPE. ► Graphene sheets exhibit good extraction efficiency for 7 PAHs. ► PAHs in river water samples were determined by the developed method.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2012 Volume 1235() pp:26-33
Publication Date(Web):27 April 2012
DOI:10.1016/j.chroma.2012.02.068
For the first time, a simple and novel one-step combined solvent bar microextraction with derivatization with GC–MS analysis, was developed for the determination of pharmaceutically active compounds (PhACs) in water samples. In the procedure, the derivatization reagent was added in the extraction solvent (solvent bar), so that the analytes could be extracted from the aqueous sample and simultaneously derivatized in the solvent bar to enhance their volatility and improve chromatographic performance. After extraction, the derivatized analytes in the extract were directly injected into a GC–MS system for analysis. Six PhACs including naproxen, ibuprofen, ketoprofen, propranolol, diclofenac, and alprenolol were used here to develop and evaluate the method. The parameters affecting the derivatization and extraction efficiency including derivatization time and temperature, the proportion of derivatization reagent, the type of organic solvent, extraction time, extraction temperature, pH of sample solution, effect of ionic strength, and sample agitation speed, were investigated in detail. Under the most favorable conditions, the method provided good limits of detection ranging from 0.006 to 0.022 μg/L, linearity (from 0.1–50 to 0.2–50 μg/L, depending on analytes) and repeatability of extractions (RSDs below 9.5%, n = 5). The proposed method was compared to hollow fiber protected liquid-phase microextraction and solid-phase microextraction, and showed higher extraction efficiency and/or shorter extraction time. The proposed method was applied to the determination of six PhACs in drain water, and was demonstrated to be simple, fast and efficient.Highlights► One-step solvent bar microextraction and derivatization of pharmaceutically active compounds. ► Separate derivatization step, necessary in many other methods, is avoided. ► Fast and efficient analytical approach with low LODs, good linearity and repeatability.
Co-reporter:Sivarajan Kanimozhi, Chanbasha Basheer, Shanmugam Neveliappan, Kelvin Ang, Feng Xue, Hian Kee Lee
Journal of Chromatography B 2012 Volume 909() pp:37-41
Publication Date(Web):15 November 2012
DOI:10.1016/j.jchromb.2012.10.008
The applicability of hollow fibre protected liquid phase microextraction (HF-LPME) for the determination of three oestrogens, namely estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) from individual zebrafish liver samples, in a bioaccumulation study on these organisms, is reported. The oestrogens were extracted from single, mechanically crushed and minced livers from fish that were heaved in tubes containing water spiked at low concentration of the analytes. Extraction was performed with ∼3 μL of toluene contained in the hollow fibre. In order to achieve high extraction efficiency, the parameters that could affect the effectiveness of HF-LPME were optimized, i.e. the extracting organic solvent, extraction time, stirring speed and pH of the aqueous phase. For gas chromatography/mass spectrometry (GC/MS) analysis, injection port derivatization of the oestrogens with bis(trimethylsilyl)trifluoroacetamide was conducted. Under the most favourable extraction and derivatization conditions, enrichment factors of 158–279 were obtained. Linearity of the HF-LPME–GC/MS method was evaluated from 1 to 50 μg/L and the coefficient of determination (r2) ranged from 0.9687 to 0.9926. The LODs were between 0.017 and 0.033 μg/L (at a signal to noise ratio of 3) with relative standard deviations (RSDs, analytes spiked at 5 μg/L) of between 15 and 17% (n = 3).Highlights► HF-LPME was used to quantitate the oestrogens from individual zebrafish liver. ► Injection port derivatization of the oestrogens was performed. ► Bioaccumulation of zebrafish liver was investigated using tank experiments.
Co-reporter:Zhenzhen Huang, Hian Kee Lee
TrAC Trends in Analytical Chemistry 2012 Volume 39() pp:228-244
Publication Date(Web):October 2012
DOI:10.1016/j.trac.2012.05.007
The marriage of materials and analytical chemistry has been an important development in sample preparation. Also, miniaturized sample preparation is gaining more interest, with the advantages of much lower consumption of organic solvents, improved labor efficiency and shorter extraction times.This review describes recent developments of sorbent-based sample-preparation methods, including primarily procedures for minimizing solvent usage and focusing on preparation and applications of interesting materials as sorbents.We discuss and assess several novel materials (i.e. graphene, ionic liquids, polymeric ionic liquids, molecularly-imprinted polymers, and metal-organic frameworks) in some of the latest published works on sample preparation.We emphasize the performance of these new sorbents in the extraction of analytes from environmental, biological and food samples, and evaluate their merits and shortcomings.Highlights► Materials-based approaches are essential in analytical sample preparation. ► We review recent developments of emerging materials in sample preparation. ► We focus on the merits and the shortcomings of materials in sample preparation.
Co-reporter:Yufeng Zhang, Hian Kee Lee
Analytica Chimica Acta 2012 750() pp: 120-126
Publication Date(Web):31 October 2012
DOI:10.1016/j.aca.2012.04.014
Co-reporter:Jingyi Lee and Hian Kee Lee
Analytical Chemistry 2011 Volume 83(Issue 17) pp:6856
Publication Date(Web):July 15, 2011
DOI:10.1021/ac200807d
A new fully automated dynamic in-syringe liquid-phase microextraction (LPME) and on-column derivatization approach, with gas chromatography/mass spectrometric (GC/MS) analysis, was developed to determine carbamate pesticides from water samples. With the use of a CTC CombiPal autosampler and its associated Cycle Composer software, a sample preparation-GC/MS method was enabled that allowed sample extraction, extract injection, and analyte derivatization to be carried out completely automatically. Optimization of extraction parameters was carried out by orthogonal array design which required a minimum of 16 experiments; the entire set of experiments was performed completely automatically and consecutively without any human intervention. Low limits of detection ranging from 0.05 to 0.1 μg/L were achieved for the carbamates. Effective enrichment of the analytes at a low concentration of 0.01 mg/L was also achieved (enrichment factors of between 57 and 138). The precision of the optimized method was satisfactory, with relative standard deviations of <6.0% (n = 6). High relative recoveries of between 81 and 125% were obtained when the method was applied to the analysis of real water samples, indicating that the sample matrix had little effect on the developed method. This automated dynamic in-syringe LPME approach demonstrated the feasibility of a complete analytical system comprising sample preparation and GC/MS that might be operated onsite, fully automatically without human intervention.
Co-reporter:Sivarajan Kanimozhi, Chanbasha Basheer, Kothandaraman Narasimhan, Lin Liu, Stephen Koh, Feng Xue, Mahesh Choolani, Hian Kee Lee
Analytica Chimica Acta 2011 Volume 687(Issue 1) pp:56-60
Publication Date(Web):14 February 2011
DOI:10.1016/j.aca.2010.12.007
A cost effective and environmentally friendly extraction technique using porous membrane protected micro-solid phase extraction (μ-SPE) is described for the extraction of estrogens in cyst fluid samples obtained from cancer patients. A sorbent (ethylsilane (C2) modified silica) (20 mg) was packed in a porous polypropylene envelope (2 cm × 1.5 cm) whose edges were heat sealed to secure the contents. The μ-SPE device was conditioned with acetone and placed in a stirred (1:5) diluted cyst fluid sample solution (10 mL) to extract estrogens for 60 min. After extraction, the analytes were desorbed and simultaneously derivatized with a 5:1 mixture of acetone and N,O-bis(trimethylsilyl)-trifluoroacetamide. The extract (2 μL) was analyzed by gas chromatography–mass spectrometry. Various extraction, desorption and derivatization conditions were optimized for μ-SPE. With this simple technique, low limits of detection of between 9 and 22 ng L−1 and linear range from the detection limits up to 50 μg L−1 were achieved. The optimized method was used to extract estrogens from cyst fluid samples obtained from patients with malignant and benign ovarian tumors.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 28) pp:4299-4306
Publication Date(Web):15 July 2011
DOI:10.1016/j.chroma.2011.05.031
For the first time, an ionic liquid based three-phase liquid–liquid–liquid solvent bar microextraction (IL-LLL-SBME) was developed for the analysis of phenols in seawater samples. The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), was used as the intermediary solvent for LLL-SBME, enhancing the extraction efficiency for polar analytes. In the procedure, the analytes were extracted from the aqueous sample into the ionic liquid intermediary and finally, back-extracted into an aqueous acceptor solution in the lumen of the hollow fiber. The porous polypropylene membrane acted as a filter to prevent potential interfering materials from being extracted, and no additional cleanup was required. After extraction, the acceptor solution could be directly injected into a high-performance liquid chromatographic system for analysis. Six phenols, 2-nitrophenol, 4-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were selected here as model compounds for developing and evaluating the method. The most influential extraction parameters were evaluated, including the ionic liquid, the composition of donor solution and acceptor solution, the extraction time and the extraction temperature, the effect of ionic strength, and the agitation speed. Under the most favorable extraction parameters, the method showed good linearity (from 0.05–50 to 0.5–50 μg/L, depending on the analytes) and repeatability of extractions (RSD below 8.3%, n = 5). The proposed method was compared to conventional three-phase LLL-SBME and ionic liquid supported hollow fiber protected three-phase liquid–liquid–liquid microextraction, and showed higher extraction efficiency. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of phenols from environmental water samples.
Co-reporter:Chanbasha Basheer, Ganapathy Balaji, Shi Hui Chua, Suresh Valiyaveettil, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 5) pp:654-661
Publication Date(Web):4 February 2011
DOI:10.1016/j.chroma.2010.12.033
A novel on-site sample preparation approach for the organophosphorus pesticides (OPPs) using functional polymer-coated fibers with a portable agitation device has been developed and demonstrated. In this approach, a handheld battery-operated electric toothbrush was used to provide agitation of the sample solution at the sampling site to facilitate extraction. A functional conjugated polymer (2-(9,9-bis(6-bromo-2-ethylhexyl)9-H-fluoren-2-yl)benzene-1,4-diamine) was coated on commercial Technora fibers (each strand consisted of 1000 filaments, each of diameter ca. 9.23 μm) which were then used for extraction. After extraction, the fibers were brought back to the laboratory in an icebox. The analytes were subsequently desorbed by organic solvent and the extract was analysed by gas chromatography–mass spectrometry. Six OPPs, triethylphosphorothiolate, thionazin, sulfotep, phorate, disulfoton and parathion were used as model compounds. Experimental parameters such as extraction time, desorption time, types of polymer fibers and fiber coatings as well the nature of desorption solvent were optimized in the laboratory prior to its on-site application of the procedure. Using optimum extraction conditions calibration curves were linear with correlation coefficient of 0.9748–0.9998 over the concentration range of 0.1–10 μg l−1. The method detection limits (at a signal-to-noise ratio of 3) were in the range of 0.3–30.3 ng l−1, which were lower than what could be achieved with solid-phase extraction performed at the laboratory. The proposed method was evaluated for the on-site extraction of OPPs in seawater samples.
Co-reporter:Dandan Ge, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 47) pp:8490-8495
Publication Date(Web):25 November 2011
DOI:10.1016/j.chroma.2011.09.077
Zeolite imidazolate framework 8 (ZIF-8) has permanent porosity, high surface area, hydrophobic property, open metal sites and remarkable water stability. These novel properties characterize the material as being different from other moisture sensitive metal–organic frameworks and endow ZIF-8 with the potential to extract trace analytes from environmental water samples. In the present study, ZIF-8 was synthesized and used as a sorbent for micro-solid-phase extraction of 6 polycyclic aromatic hydrocarbons (PAHs) from environmental water samples for the first time. Parameters influencing the extraction efficiency such as desorption time, extraction time, desorption solvent and salt concentration were investigated. Environmental water samples collected from a local lake were processed using this novel μ-SPE procedure. ZIF-8 proved to be a very efficient extraction sorbent for the extraction of trace analytes from water samples. The limits of detection from gas chromatography–mass spectrometric analysis of PAHs were 0.002–0.012 ng/ml. The linear ranges were 0.1–50 or 0.5–50 ng/ml. The relative standard deviations for five replicates of the extractions were in the range of 2.1–8.5%.Highlights► Zeolite imidazolate framework 8 (ZIF-8) as novel extraction sorbent is demonstrated. ► ZIF-8 is very stable when it is used in aqueous samples. ► ZIF-8 shows very good performance for PAH extraction from environmental water samples.
Co-reporter:Hong Zhang, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 28) pp:4509-4516
Publication Date(Web):15 July 2011
DOI:10.1016/j.chroma.2011.05.016
A solid-phase microextraction (SPME) device, assembled with a commercially available plunger-in-needle microsyringe, with the plunger coated with graphene via a sol–gel approach, was developed for the gas chromatographic–mass spectrometric determination of polybrominated diphenyl ethers (PBDEs) in environmental samples. This is the first application of graphene-based sol–gel coating as SPME sorbent. Parameters affecting the extraction efficiency were investigated in detail. The new coating exhibited enrichment factors for PBDEs between 1378 and 2859. The unique planar structure of graphene enhanced the π–π interaction with the aromatic PBDEs; additionally, the sol–gel coating technique created a porous three-dimensional network structure which offered larger surface area for extraction. The stainless steel plunger provided firm support for the coating and enhanced the durability of the assembly. The plunger-in-needle microsyringe represents a ready-made tool for SPME implementation. Under the optimized conditions, the method detection limits for five PBDEs were in the range of 0.2 and 5.3 ng/L (at a signal/noise ratio of 3) and the precision (% relative standard deviation, n = 5) was 3.2–5.0% at a concentration level of 100 ng/L. The linearities were 5–1000 or 10–1000 ng/L for different PBDEs. Finally, the proposed method was successfully applied to the extraction and determination by gas chromatography–mass spectrometry of PBDEs in canal water samples.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 31) pp:5040-5046
Publication Date(Web):5 August 2011
DOI:10.1016/j.chroma.2011.05.069
For the first time, the low-density solvent-based solvent demulsification dispersive liquid–liquid microextraction was developed for the fast, simple, and efficient determination of 16 priority polycyclic aromatic hydrocarbons (PAHs) in environmental samples followed by gas chromatography–mass spectrometric (GC–MS) analysis. In the extraction procedure, a mixture of extraction solvent (n-hexane) and dispersive solvent (acetone) was injected into the aqueous sample solution to form an emulsion. A demulsification solvent was then injected into the aqueous solution to break up the emulsion, which turned clear and was separated into two layers. The upper layer (n-hexane) was collected and analyzed by GC–MS. No centrifugation was required in this procedure. Significantly, the extraction needed only 2–3 min, faster than conventional DLLME or similar techniques. Another feature of the procedure was the use of a flexible and disposable polyethylene pipette as the extraction device, which permitted a solvent with a density lighter than water to be used as extraction solvent. This novel method expands the applicability of DLLME to a wider range of solvents. Furthermore, the method was simple and easy to use, and some additional steps usually required in conventional DLLME or similar techniques, such as the aforementioned centrifugation, ultrasonication or agitation of the sample solution, or refrigeration of the extraction solvent were not necessary. Important parameters affecting the extraction efficiency were investigated in detail. Under the optimized conditions, the proposed method provided a good linearity in the range of 0.05–50 μg/L, low limits of detection (3.7–39.1 ng/L), and good repeatability of the extractions (RSDs below 11%, n = 5). The proposed method was successfully applied to the extraction of PAHs in rainwater samples, and was demonstrated to be fast, efficient, and convenient.
Co-reporter:Liang Guo, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 52) pp:9321-9327
Publication Date(Web):30 December 2011
DOI:10.1016/j.chroma.2011.10.066
Micro-solid-phase extraction (μ-SPE) was developed for the determination of trace level of 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons (PAHs) in river water samples with gas chromatography–mass spectrometry (GC–MS). In the μ-SPE device, multiwalled carbon nanotubes was employed as sorbent and was packed inside an porous polypropylene membrane “envelope” whose edges were heat-sealed to secure the contents. The μ-SPE device was placed in a stirred sample solution to extract the analytes. The porous polypropylene membrane envelope in μ-SPE device acts as a filter to exclude potential interferences, such as eliminating or reducing the influence of particles that are bigger than the pore size. After extraction, analyte desorption was carried out with a suitable organic solvent under ultrasonication. Important extraction parameters were optimized in detail, including the selection and amount of sorbent materials, the extraction temperature and extraction time, desorption solvent and desorption time, amount of organic modifier, agitation speed and sample ionic strength. Under the developed extraction conditions, the proposed method provided good linearity in the range of 0.1–50 μg/L, low limits of detection (4.2–46.5 ng/L), and good repeatability of the extractions (relative standard deviations, <12%, n = 5). The developed μ-SPE method was successfully applied to the extraction of PAHs in river water samples. The μ-SPE method was demonstrated to be a fast and efficient method for the determination of PAHs from environmental water samples.Highlights► Multiwalled carbon nanotubes were employed as an efficient sorbent in μ-SPE. ► Suitable for complex aqueous matrices. ► Simple, fast and efficient approach with low LODs, good linearity and repeatability.
Co-reporter:Chanbasha Basheer, Weishan Wong, Ahmad Makahleh, Abdassalam Abdelhafiz Tameem, Abdussalam Salhin, Bahruddin Saad, Hian Kee Lee
Journal of Chromatography A 2011 Volume 1218(Issue 28) pp:4332-4339
Publication Date(Web):15 July 2011
DOI:10.1016/j.chroma.2011.04.073
Eight hydrazone-based ligands were synthesized, trapped in a silica sol–gel matrix, and were subsequently used in the micro-solid phase extraction (μ-SPE) of biogenic amines (BAs). The BAs investigated were tryptamine, phenylethylamine, putrescine, histamine, tyramine and spermidine. Prior to the extraction, dansyl chloride was added to the samples which were heated to 70 °C for 10 min. The samples were extracted with μ-SPE, after which analytes were desorbed using acetonitrile via ultrasonication. The extracts were analysed by high performance liquid chromatography (HPLC) with ultraviolet detection. Of the eight ligands investigated as sorbents, benzophenone 2,4-dinitrophenylhydrazone was found to be the most promising. The enhanced π–π interaction between the analytes and the ligand facilitated the adsorption process. Under the most suitable extraction conditions, the method demonstrated good linearity with correlation coefficient of more than 0.985 over a concentration range of 1–50 μg L−1. Satisfactory repeatability with relative standard deviations of 7.43–11.30% (n = 3) were obtained. Detection limits ranged from 3.8 to 31.3 ng L−1. The μ-SPE method exhibited lower recoveries (71.5–87.4%) when compared to the solid phase extraction technique (79.7–95.0%), but enrichment factors of 94–460 were obtained. The proposed μ-SPE-HPLC method was applied to the determination of BAs in orange juice purchased from local supermarkets, with satisfactory results. The orange juices were characterized by the presence of relatively high levels of putrescine (range, 550–2210 μg L−1) but tryptamine and phenylethylamine were not detected in any of the tested samples.
Co-reporter:Khalid Alhooshani, Chanbasha Basheer, Jagjit Kaur, Astrid Gjelstad, Knut E. Rasmussen, Stig Pedersen-Bjergaard, Hian Kee Lee
Talanta 2011 Volume 86() pp:109-113
Publication Date(Web):30 October 2011
DOI:10.1016/j.talanta.2011.08.026
For the first time, haloacetic acids and aromatic acetic acids were extracted from wastewater samples using electromembrane extraction (EME). A thin layer of toluene immobilized on the walls of a polypropylene membrane envelope served as an artificial supported liquid membrane (SLM). The haloacetic acids (HAAs) (chloroacetic acid, dichloroacetic acid, and trifluoroacetic acid) and aromatic acetic acids (phenylacetic acid and p-hydroxyphenylacetic acid) were extracted through the SLM and into an alkalized aqueous buffer solution. The buffer solution was located inside the membrane envelope. The electrical potential difference sustained over the membrane acted as the driving force for the transport of haloacetic acids into the membrane by electrokinetic migration. After extraction, the extracts were analyzed by high-performance liquid chromatography-ultraviolet detection. The detection limits were between 0.072 and 40.3 ng L−1. The calibration plot linearity was in the range of 5 and 200 μg L−1 while the correlation coefficients for the analytes ranged from 0.9932 to 0.9967. Relative recoveries were in the range of 87–106%. The extraction efficiency was found to be comparable to that of solid-phase extraction.
Co-reporter:Zhi-Guo Shi and Hian Kee Lee
Analytical Chemistry 2010 Volume 82(Issue 4) pp:1540
Publication Date(Web):January 21, 2010
DOI:10.1021/ac9023632
A new two-step microextraction technique, combining dispersive liquid−liquid microextraction (DLLME) and dispersive microsolid-phase extraction (D-μ-SPE), was developed for the fast gas chromatographic-mass spectrometric determination of polycyclic aromatic hydrocarbons (PAHs) in environmental samples. A feature of the new procedure lies in that any organic solvent immiscible with water can be used as extractant in DLLME. A special apparatus, such as conical-bottom test tubes, and tedious procedures of centrifugation, refrigeration of the solvent, and then thawing it, associated with classical DLLME or similar techniques are not necessary in the new procedure, which potentially lends itself to possible automation. In the present D-μ-SPE approach, hydrophobic magnetic nanoparticles were used to retrieve the extractant of 1-octanol in the DLLME step. It is noteworthy that the target of D-μ-SPE was the 1-octanol rather than the PAHs. Because of the rapid mass transfer associated with the DLLME and the D-μ-SPE steps, fast extraction could be achieved. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: vortex at 3200 rpm in the DLLME step for 2 min and in D-μ-SPE for 1 min and then desorption by sonication for 4 min with acetonitrile as the solvent. The results demonstrated that enrichment factors ranging from 110- to 186-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 11.7−61.4 pg/mL and 0.04−0.21 ng/mL, respectively. The linearities were 0.5−50, 1−50, or 2−50 ng/mL for different PAHs. Finally, the two-step extraction method was successfully used for the fast determination of PAHs in river water samples. This two-step method, combining two different and efficient miniaturized techniques, provides a fast means of sample pretreatment for environmental water samples.
Co-reporter:Chanbasha Basheer, Jingyi Lee, Stig Pedersen-Bjergaard, Knut Einar Rasmussen, Hian Kee Lee
Journal of Chromatography A 2010 Volume 1217(Issue 43) pp:6661-6667
Publication Date(Web):22 October 2010
DOI:10.1016/j.chroma.2010.04.066
The simultaneous extraction of acidic and basic analytes from a particular sample is a challenging task. In this work, electromembrane extraction (EME) of acidic non-steroidal anti-inflammatory drugs and basic β-blockers in a single step was carried out for the first time. It was shown that by designing an appropriate compartmentalized membrane envelope, the two classes of drugs could be electrokinetically extracted by a 300 V direct current electrical potential. This method required only a very short 10-min extraction time from a pH-neutral sample, with a small amount (50 μL) of organic solvent (1-octanol) as the acceptor phase. Analysis was carried out using gas chromatography–mass spectrometry after derivatization of the analytes. Extraction parameters such as extraction time, applied voltage, pH range, and concentration of salt added were optimized. The proposed EME technique provided good linearity with correlation coefficients from 0.982 to 0.997 over a concentration range of 1–200 μg L−1. Detection limits of the drugs ranged between 0.0081 and 0.26 μg L−1, while reproducibility ranged from 6 to 13% (n = 6). Finally, the application of the new method to wastewater samples was demonstrated.
Co-reporter:Zhi-Guo Shi, Yufeng Zhang, Hian Kee Lee
Journal of Chromatography A 2010 Volume 1217(Issue 47) pp:7311-7315
Publication Date(Web):19 November 2010
DOI:10.1016/j.chroma.2010.09.049
A new mode of liquid-phase microextraction based on a ferrofluid has been developed. The ferrofluid was composed of silica-coated magnetic particles and 1-octanol as the extractant solvent. The 1-octanol was firmly confined within the silica-coated particles, preventing it from being lost during extraction. Sixteen polycyclic aromatic hydrocarbons (PAHs) were used as model compounds in the development and evaluation of the extraction procedure in combination with gas chromatography–mass spectrometry. Parameters affecting the extraction efficiency were investigated in detail. The optimal conditions were as follows: 20 mL sample volume, 10 mg of the silica-coated magnetic particles (28 mg of ferrofluid), agitation at 20 Hz, 20 min extraction time, and 2 min by sonication with 100 μL acetonitrile as the final extraction solvent. Under optimal extraction conditions, enrichment factors ranging from 102- to 173-fold were obtained for the analytes. The limits of detection and the limits of quantification were in the range of 16.8 and 56.7 pg mL−1 and 0.06 and 0.19 ng mL−1, respectively. The linearities were between 0.5–100 and 1–100 ng mL−1 for different PAHs. As the ferrofluid can respond to and be attracted by a magnet, the extraction can be easily achieved by reciprocating movement of an external magnet that served to agitate the sample. No other devices were needed in this new approach of extraction. This new technique is affordable, efficient and convenient for microextraction, and offers portability for potential onsite extraction.
Co-reporter:Li Xu, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2010 Volume 1217(Issue 39) pp:6036-6043
Publication Date(Web):24 September 2010
DOI:10.1016/j.chroma.2010.07.072
Solvent-bar microextraction (SBME) based on two-phase (water-to-organic) extraction was for the first time used as the sample pretreatment method for the non-aqueous capillary electrophoresis (NACE) of herbicides of environmental concern. Due to the compatibility of the extractant organic solvent and the NACE separation system, the extract could be introduced directly to the CE system after SBME. Through investigations of the effect of sample pH, extraction time, agitation speed and salt addition on extraction efficiency, the most suitable extraction conditions were determined: sample solution at a pH of 1, without added salt, and stirring at 700 revolutions per minute for 30 min. SBME as applied here was also compared with single-drop microextraction and hollow fiber-protected liquid-phase microextraction. SBME showed the highest extraction efficiency. In addition, field-amplified sample injection with pre-introduced organic solvent plug removal using the electroosmotic flow as a pump (FAEP) was used to enhance the sensitivity further in NACE. Based on studies of the effect of different organic solvents, different lengths of the organic plugs and different volumes of sample injection on stacking efficiency under the most suitable separation conditions, methanol was found to be the most efficient solvent for on-line preconcentration. Combined with SBME, FAEP-NACE achieved limits of detection of between 0.08 ng/mL and 0.14 ng/mL for the studied analytes. This preconcentration approach for NACE was demonstrated to be amenable to aqueous environmental samples by applying it to spiked river water.
Co-reporter:Chanbasha Basheer, Shruti Pavagadhi, Huixin Yu, Rajasekhar Balasubramanian, Hian Kee Lee
Journal of Chromatography A 2010 Volume 1217(Issue 41) pp:6366-6372
Publication Date(Web):8 October 2010
DOI:10.1016/j.chroma.2010.08.012
A simple and rapid extraction procedure was developed for determining aldehydes in rainwater samples. This extraction technique involved the use of micro-solid-phase extraction in which the sorbent was held within a polypropylene membrane envelope, followed by high-performance liquid chromatographic analysis. Aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and valeraldehyde were used as model compounds. Extraction conditions were optimized. The method linearity ranged between 0.5 and 50 μg l−1 with the correlation coefficient of 0.987–0.999. The relative standard deviations (RSDs) of the method ranged from 7 to 12%. Method detection limits were in the range of 0.07–0.15 μg l−1, which is lower than those previously reported for solid-phase microextraction combined with gas chromatography–mass spectrometric techniques. The proposed extraction technique was used for determination of aldehydes in rainwater samples to demonstrate the applicability of the method.
Co-reporter:Sini George and Hian Kee Lee
Analytical Methods 2010 vol. 2(Issue 4) pp:326-334
Publication Date(Web):02 Feb 2010
DOI:10.1039/B9AY00300B
A nanocomposite was prepared using single walled carbon nanotubes (SWCNTs) and thiol-derivatised gold nanoparticles (Aunano). Transmission electron microscopy (TEM) image of the nanocomposite showed that the Aunano were self-assembled on to the side walls of the SWCNTs after the modification process. Moreover, from the TEM analysis, it was clear that the likelihood of agglomeration of these nanoparticles in the nanocomposite were rare. A film of the nanocomposite was then applied on a glassy carbon electrode (GCE). The nanocomposite modified GCE was used for the electrochemical detection of several carcinogenic polycyclic aromatic amines (PAAs) simultaneously. The combination of the adsorptive properties of SWCNTs with an enhanced electroactive surface area, electrical conductivity of Aunano, together with the interaction of the amino group of the analytes and Aunano permitted very efficient detection of the analytes. Preconcentration and detection of the analytes in the real samples could be achieved in a single step using adsorptive stripping voltammetry (ASV). ASV for the PAAs achieved detection limits in the range of 1 μg L−1 (using 9,10-diaminophenanthrene as an example), with linearity up to 3 orders of magnitude. Moreover, the nanocomposite modified electrode exhibited excellent selectivity with high reproducibility towards several PAAs and resulted in their simultaneous and sensitive detection with detection limits in the μg L−1 range. Using 9,10-diaminophenanthrene as an example, the reproducibility of the analyte signal in the simultaneous detection of several PAAs was determined to be within 5% (n = 8) from one electrode preparation to another, and the response signal was stable (±4.5% at 95% confidence interval) for 15 repeated analyses with 600 s of preconditioning. Applicability of the procedure to tap water, river water, and wastewater samples was demonstrated. Such nanocomposite devices hold great promise for convenient and sensitive environmental screening of carcinogenic PAAs.
Co-reporter:Jie Zhang, Hian Kee Lee
Talanta 2010 Volume 81(1–2) pp:537-542
Publication Date(Web):15 April 2010
DOI:10.1016/j.talanta.2009.12.039
Headspace microdrop liquid-phase microextraction (LPME) using ionic liquids as extracting solvents, followed by gas chromatography–electron capture detection was successfully developed to determine organochlorine pesticides in soil samples. A feature of the developed procedure is the simple handling of the ionic liquid extract in a normal, unmodified gas chromatograph injection port such that no special provision was needed to ensure that the ionic liquid did not contaminate it. This was achieved by only exposing the ionic liquid extract in the injection port while it was still attached to the syringe needle tip (i.e. mirroring the extraction configuration) to permit volatilization of the analytes, instead of injecting the extract. In this way, the spent ionic liquid could be recovered from the injection port, obviating the need to clean the port. Four 1-butyl-3-methylimidazolium-based ionic liquids were investigated, and 1-butyl-3-methylimidazolium hexafluorophosphate was finally selected as the most suitable extracting solvent. Parameters that affect the extraction and determination of the organochlorine pesticides were studied. Under the optimal conditions, the proposed method produced good linearity over a concentration range of 5–250 ng/g. Limits of detection ranging from 0.25 to 0.5 ng/g were achieved.
Co-reporter:Li Xu, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 38) pp:6549-6553
Publication Date(Web):18 September 2009
DOI:10.1016/j.chroma.2009.07.056
Polyvinyl chloride (PVC) fiber was derivatized by concentrated sulfuric acid to yield sulfonated PVC (PVC-SO3H). The PVC-SO3H fiber had dual properties as a sorbent, based on cation-exchange and hydrophobicity. In the present study, the novel fiber was used directly as an individual device for extraction purposes in the cation-exchange microextraction of anaesthetics, followed by high-performance liquid chromatography-UV analysis. The results demonstrated that this PVC-SO3H fiber-based microextraction afforded convenient operation and cost-effective application to basic analytes. The limits of detection for four anaesthetics ranged from 1.2 to 6.0 ng/mL. No carryover (because of its disposable usage), and no loss of sorbent phase (which normally occurs in stir-bar sorptive extraction) during extraction were observed.
Co-reporter:Li Xu, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 29) pp:5483-5488
Publication Date(Web):17 July 2009
DOI:10.1016/j.chroma.2009.05.074
In this paper, a novel liquid-phase microextraction (LPME) approach, based on solvent-bar microextraction (SBME), was developed in which a silica monolith was used as the extractant solvent holder. Owing to the porous nature of the monolith, the extractant solvent could be easily held in the material; when the monolith containing the extractant solvent was exposed to the sample solution, analytes could directly diffuse from the sample solution into the extractant solvent. Polycyclic aromatic hydrocarbons (PAHs) were used as model analytes to evaluate the procedure. Through the investigation of the effect of agitation speed, extraction time, length of the monolith (that determined the volume of organic extractant solvent) and salt concentration on extraction efficiency, the following optimal extraction conditions were obtained: stirring at 1000 rpm for 30 min without salt addition using a 4-mm silica monolith. The limits of detection ranged from 3.9 pg/mL to 28.8 pg/mL, with relative standard deviations of between 8.16% and 10.5% on the same silica monolith. The linearity was 0.05–200 ng/mL for fluoranthene and pyrene, and 0.5–200 ng/mL for chrysene and benzo[b]fluoranthene, with acceptable correlation coefficient. When this method was applied for the spiked real river sample, the relative recoveries ranged from 87.1% to 100.7% for the tested PAHs. This method was also compared to polymeric hollow fiber-based SBME and hollow fiber-protected LPME and found to provide better results. Additionally, compared with the polymeric hollow fiber, the silica monolith possesses good resistance to extreme conditions, such as high temperature and pH, and is more compatible with various organic solvents. This is the first report of an application of a monolithic material for LPME, and as a solvent holder for SBME. It extends the scope of applications of such materials, to analytical chemistry, specifically to sample preparation.
Co-reporter:Jie Zhang, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 44) pp:7527-7532
Publication Date(Web):30 October 2009
DOI:10.1016/j.chroma.2009.03.051
A method has been established for the determination of four pharmaceutically active compounds (ibuprofen, ketoprofen, naproxen and clofibric acid) in water samples using dynamic hollow fiber liquid-phase microextraction (HF/LPME) followed by gas chromatography (GC) injection port derivatization and GC–mass spectrometric (MS) determination. Dynamic HF/LPME is a novel approach to microextraction that involves the use of a programmable syringe pump to move the liquid phases participating in the extraction so as to facilitate the process. Trimethylanilinium hydroxide (TMAH) was used as derivatization reagent for the analytes to increase their volatility and improve chromatographic separation. Parameters that affect extraction efficiency (selection of organic solvent, volume of organic solvent, agitation in the donor phase, plunger movement and extraction time) were investigated. Under optimal conditions, the proposed method provided good enrichment factors up to 251, reproducibility ranging from 3.26% to 10.61%, and good linearity from 0.2 to 50 μg/L. The limits of detection ranged between 0.01 and 0.05 μg/L (S/N = 3) using selective ion monitoring. This method was applied to the determination of the four pharmaceutically active compounds in tap water and wastewater collected from a drain in the vicinity of a hospital.
Co-reporter:Toh Ming Hii, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 44) pp:7520-7526
Publication Date(Web):30 October 2009
DOI:10.1016/j.chroma.2009.09.019
A novel microextraction method making use of commercial polymer fiber as sorbent, coupled with high-performance liquid chromatography-fluorescence detection for the determination of polycyclic aromatic hydrocarbons (PAHs) in water has been developed. In this technique, the extraction device was simply a length (8 cm) of a strand of commercial polymer fiber, Kevlar (each strand consisted of 1000 filaments, each of diameter ca. 9.23 μm), that was allowed to tumble freely in the aqueous sample solution during extraction. The extracted analytes were desorbed ultrasonically before the extract was injected into HPLC system for analysis. Extraction parameters such as extraction time, desorption time, type of desorption solvent and sample volume were optimized. Each fiber could be used for up to 50 extractions and the method showed good precision, reproducibility and linear response within a concentration range 0.05–5.00 μg L−1 with correlation coefficients of up to 0.9998. Limits of detection between 0.4 and 4.4 ng L−1 for seven PAHs could be achieved. The relative standard deviations (n = 3) of this technique were between 2.9% and 12.1%.
Co-reporter:Li Xu, Peter C. Hauser, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 31) pp:5911-5916
Publication Date(Web):31 July 2009
DOI:10.1016/j.chroma.2009.06.026
In the present study, field-amplified sample stacking injection using the electroosmotic flow pump (FAEP) was developed for the capillary electrophoretic separation of the four nerve agent degradation products methylphosphonic acid (MPA), ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA) and cyclohexyl methylphosphonic acid (CMPA). Coupled to contactless conductivity detection, direct quantification of these non-UV active compounds could be achieved. Sensitivity enhancement of up to 500 to 750-fold could be obtained. The newly established approach was applied to the determination of the analytes in river water and aqueous extracts of soil. Detection limits of 0.5, 0.7, 1.4 and 2.7 ng/mL were obtained for MPA, EMPA, IMPA and CMPA, respectively, in river water and 0.09, 0.14, 0.44 and 0.22 μg/g, respectively, in soil.
Co-reporter:Chanbasha Basheer, Anass Ali Alnedhary, B.S. Madhava Rao, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 2) pp:211-216
Publication Date(Web):9 January 2009
DOI:10.1016/j.chroma.2008.11.042
We describe a simple and sensitive porous polypropylene membrane-protected micro-solid-phase extraction (μ-SPE) approach for the sample preparation and determination of carbamate pesticides in soil samples by high-performance liquid chromatography. The μ-SPE device consisted of C18 sorbent held within a porous polypropylene envelope. In order to achieve optimum performance, several extraction parameters were optimized. Under the most favorable conditions, the extraction efficiency of the μ-SPE was very high, with detection limits in the range of 0.01–0.40 ng g−1. This is more than two orders of magnitude lower than the limits obtained by the United States Environmental Protection Agency Methods 8321A and 8318. A linear relationship was obtained for each analyte in the range of 2 and 200 ng g−1. The relative standard deviation for the analysis of aged soil samples spiked at 5 ng g−1 was ≤11%. The reproducibility of separate μ-SPE device used for experiments was satisfactory (relative standard deviations ranged from 4 to 11%), indicating that the method is reliable for routine environmental analysis.
Co-reporter:Li Xu, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2009 Volume 1216(Issue 4) pp:701-707
Publication Date(Web):23 January 2009
DOI:10.1016/j.chroma.2008.10.005
In recent years, liquid-phase microextraction (LPME), a microscale implementation of liquid–liquid extraction, has become a very popular sample pretreatment technique because it combines extraction and enrichment, and is inexpensive, easy to operate and nearly solvent-free. Especially so in hollow fiber-protected LPME, sample cleanup is also effected. Essentially, owing to its high sample-to-extracting solvent volume ratio, LPME can achieve high analyte enrichment. Since its advent, the technique has been widely used, and applied to environmental, pharmaceutical, biological and forensic analyses. This review focuses on developments relating to chemical reactions associated with LPME applications, in contrast to conventional, straightforward extractions in which analytes remain as they are during the extraction process. Chemical reactions brought about during LPME serve to promote the extractability of the analytes (thus expanding the scope of applicability of the technique), facilitate their (analyte) compatibility with the analytical system and/or improve detection sensitivity. The reactions that are usually enabled during LPME include ion-pair extraction (carrier-mediated membrane transport), complexation, chemical (pre-extraction, in situ, and post-extraction) derivatization, phase-transfer catalysis and other “special affinity” reactions. Strategies on chemical reactions in LPME are overviewed in this report.
Co-reporter:Jingyi Lee, Faezeh Khalilian, Habib Bagheri, Hian Kee Lee
Journal of Chromatography A 2009 1216(45) pp: 7687-7693
Publication Date(Web):
DOI:10.1016/j.chroma.2009.09.037
Co-reporter:Sini George and Hian Kee Lee
The Journal of Physical Chemistry B 2009 Volume 113(Issue 47) pp:15445-15454
Publication Date(Web):November 2, 2009
DOI:10.1021/jp905690a
The use of heat treated carbon nanofibers, known as carbon nanochips (CNCs) for the studies of the direct electrochemistry and electrocatalytic properties of heme proteins, is demonstrated. A glassy carbon electrode (GCE) was modified with CNCs, and hemoglobin (Hb) was immobilized on the modified electrode surface by casting a film of Hb. Nafion was employed to fix the CNCs and Hb tightly on the surface of the GCE. The modified electrode was characterized by scanning electron microscopy. Ultraviolet−visible and Fourier transform infrared spectroscopy showed that Hb immobilized in the CNC film remained in its native structure. Electrochemical impedance spectroscopy and cyclic voltammetry (CV) were employed for electrochemical studies. The results showed that the presence of CNCs in the film can greatly enhance the electrochemical response of Hb. A pair of well-defined reversible CV peaks was observed, and the formal potential of the heme Fe(III)/Fe(II) redox couple was found to be −253 mV [vs Ag/AgCl (saturated KCl)]. The apparent heterogeneous electron-transfer rate constant (ks) was estimated as 2.54 s−1. The modified electrode showed excellent electrocatalytic behavior to hydrogen peroxide (H2O2), trichloroacetic acid, and sodium nitrite. H2O2 had a linear current response from 0.5 to 30 μM (R2 = 0.9997; n = 5) with a detection limit of 0.05 μM when the signal-to-noise ratio was 3 and the apparent Michaelis−Menten constant (Kmapp) was 21.55 μM. These values suggest that CNCs are the best matrix described so far for the development of biosensors, far superior to untreated carbon nanofibers. The direct immobilization of proteins onto the surface of CNCs is shown to be a highly efficient method for the development of a new class of very sensitive, stable, and reproducible electrochemical biosensors.
Co-reporter:Jingyi Lee, Hian Kee Lee, Knut E. Rasmussen, Stig Pedersen-Bjergaard
Analytica Chimica Acta 2008 Volume 624(Issue 2) pp:253-268
Publication Date(Web):29 August 2008
DOI:10.1016/j.aca.2008.06.050
In hollow fiber membrane liquid-phase microextraction (LPME), target analytes are extracted from aqueous samples and into a supported liquid membrane (SLM) sustained in the pores in the wall of a small porous hollow fiber, and further into an acceptor phase present inside the lumen of the hollow fiber. The acceptor phase can be organic, providing a two-phase extraction system compatible with capillary gas chromatography, or the acceptor phase can be aqueous resulting in a three-phase system compatible with high-performance liquid chromatography or capillary electrophoresis. Due to high enrichment, efficient sample clean-up, and the low consumption of organic solvent, substantial interest has been devoted to LPME in recent years. This paper reviews important applications of LPME with special focus on bioanalytical and environmental chemistry, and also covers a new possible direction for LPME namely electromembrane extraction, where analytes are extracted through the SLM and into the acceptor phase by the application of electrical potentials.
Co-reporter:Li Xu, Xiao Yang Gong, Hian Kee Lee, Peter C. Hauser
Journal of Chromatography A 2008 Volume 1205(1–2) pp:158-162
Publication Date(Web):26 September 2008
DOI:10.1016/j.chroma.2008.08.005
The four nerve agent degradation products methylphosphonic acid (MPA), ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA) and cyclohexyl methylphosphonic acid (CMPA) have been successfully extracted from aqueous sample solution by ion-pair liquid–liquid–liquid microextraction. In this procedure, the target analytes in the sample solution were converted into their ion-pair complexes with tri-n-butyl amine and then extracted by an organic solvent (1-octanol) layer on top of the sample solution. Simultaneously, the analytes were back-extracted into a drop of an aqueous acceptor solution which was suspended in the organic phase at a microsyringe needle tip. The factors influential to extraction: type of organic solvent, type of ion-pair reagent and its concentration, pH values of sample solution and acceptor aqueous phase, stirring rate and extraction time were investigated in detail. After extraction, the drop of the acceptor solution was withdrawn into the syringe and injected into a capillary electrophoresis system for analysis. Using contactless conductivity detection, direct quantification of these compounds is possible. Moreover, large-volume sample injection was employed for further preconcentration. Improvements in the limits of detection between 2.5 and 4 orders of magnitude could be achieved and concentrations at the ng/mL level can be determined. This newly established approach was successfully applied to a spiked river water sample.
Co-reporter:Li Xu, Peter C. Hauser, Hian Kee Lee
Journal of Chromatography A 2008 Volume 1214(1–2) pp:17-22
Publication Date(Web):19 December 2008
DOI:10.1016/j.chroma.2008.10.058
In the present study, electro membrane isolation (EMI) of four nerve agent degradation products has been successfully explored. In the procedure, a polypropylene sheet membrane folded into an envelope with an open end with its wall pores impregnated with 1-octanol was employed as the artificial supported liquid membrane (SLM). The envelope containing the extractant or aqueous acceptor phase (at pH 6.8) was immersed in the sample or donor phase (also aqueous at a pH of 6.8) for extraction. This ensured that the target analytes were fully ionized. A voltage was then applied, with the negative electrode placed in the donor phase with agitation, and the positive electrode in the acceptor phase. The ionized analytes were thus driven to migrate from the donor phase across the SLM to the acceptor phase. The factors influential to extraction: type of organic solvent, voltage, agitation speed, extraction time, pH of the donor and acceptor phase and concentration of humic acids were investigated in detail. After extraction, the acceptor phase was collected and directly injected for capillary electrophoretic (CE) analysis. Combined with capacitively coupled contactless conductivity detection (C4D), the direct detection of these compounds could be achieved. Moreover, large-volume sample injection was employed to further enhance the sensitivity of this method. Limits of detection (LODs) as low as ng/mL were reached for the studied analytes, with overall LOD enhancements of four orders of magnitude.
Co-reporter:Chanbasha Basheer, Anass Ali Alnedhary, B.S. Madhava Rao, Rajasekhar Balasubramanian, Hian Kee Lee
Journal of Chromatography A 2008 Volume 1210(Issue 1) pp:19-24
Publication Date(Web):7 November 2008
DOI:10.1016/j.chroma.2008.09.040
For the first time hollow fiber-protected ionic liquid supported three-phase (liquid–liquid–liquid) microextraction (HFM-LLLME) was developed for the gas chromatography-mass spectrometric (GC-MS) analysis of aromatic and aliphatic hydrocarbons. The hydrocarbons were extracted from 10 m1 of aqueous samples though small volumes of ionic liquid and organic solvent in the hollow fiber membrane HFM) wall and channel, respectively. The ionic liquid was immiscible with both the aqueous sample and the organic solvent (toluene). After extraction, the enriched solvent was directly injected into a GC-MS system for analysis without any further pretreatment. Ionic liquid supported HFM-LLLME shows better extraction performance than two-phase HFM-liquid-phase microextraction, in which only organic solvent is involved, and solid-phase microextraction. The ionic liquid and organic solvent combination found most suitable for HFM-LLLME was 1-butyl-3-methylimidazolium hexafluorophosphate, and toluene, respectively. This new technique provided up to 210-fold enrichment of aliphatic and aromatic hydrocarbons in 40 min with good reproducibility (<11%) and limits of detection (1–7 ng l−1).
Co-reporter:Chanbasha Basheer, Kothandaraman Narasimhan, Meihui Yin, Changqing Zhao, Mahesh Choolani, Hian Kee Lee
Journal of Chromatography A 2008 Volume 1186(1–2) pp:358-364
Publication Date(Web):4 April 2008
DOI:10.1016/j.chroma.2007.10.015
A novel, simple and efficient method for determining persistent organic pollutants (POPs) in tissue samples has been developed. This technique involves the use of simultaneous microwave-assisted digestion (MAD) and micro-solid-phase extraction (μ-SPE), in which the sorbent is held within a propylene membrane envelope, with gas chromatographic–mass spectrometric (GC–MS) analysis. The POPs studied included eleven organochlorine pesticides and five polychlorinated biphenyl congeners. Optimization of the MAD–μ-SPE parameters was performed. The relative standard deviations (RSDs) of the method ranged from 0.14 to 12.7%. Correlation coefficients up to 0.9999 were obtained across a concentration range of 1.25–50 ng g−1. The method detection limits for POPs ranged from 0.002 to 0.009 ng g−1. A preliminary study applying the MAD–μ-SPE procedure to human ovarian cancer tissue showed that it was capable of detecting the presence of a wide spectrum of different POPs in benign and malignant tumors.
Co-reporter:Hoi Sim Nancy Lee, Mui Tiang Sng, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2008 Volumes 1196–1197() pp:125-132
Publication Date(Web):4 July 2008
DOI:10.1016/j.chroma.2008.04.027
Hollow fibre-protected liquid-phase microextraction (HF-LPME) together with gas chromatography–mass spectrometry was, for the first time, investigated for the in-situ derivatisation and analysis of basic degradation products of chemical warfare agents in water samples. The degradation products studied were those of nerve and blister agents, and a psychotomimetic agent. Extractions with in-situ derivatisation were successfully performed using a mixture of solvent and derivatising agent. The protection of the moisture-sensitive derivatising agent was afforded by the hydrophobic hollow fibre. Parameters such as type of derivatising agent, extraction solvent, pH, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The linear range established was between 0.05 and 25 μg ml−1 depending on analyte, with squared regression coefficients ranging from 0.9959 to 0.9996. Relative standard deviations (RSDs) ranged from 6% to 10%. As comparison, solid-phase microextraction (SPME) was also evaluated and extraction conditions such as pH, salt concentration, stirring speed and extraction time were optimised. This work also represented the first report of such an in-situ derivatisation approach for SPME of basic analytes. The linear range established was between 0.5 and 25 μg ml−1 depending on analyte, with squared regression coefficients ranging from 0.9946 to 0.9998. RSDs ranged from 5% to 22%. The limits of detection of HF-LPME (0.04–0.36 μg l−1) showed improvement over those of SPME (0.06–0.77 μg l−1).
Co-reporter:Chanbasha Basheer, Anass Ali Alnedhary, B.S. Madhava Rao, Hian Kee Lee
Analytica Chimica Acta 2007 Volume 605(Issue 2) pp:147-152
Publication Date(Web):19 December 2007
DOI:10.1016/j.aca.2007.10.006
A simple and efficient binary solvent-based two-phase hollow fiber membrane (HFM)-protected liquid-phase microextraction (BN-LPME) technique for moderately polar compounds was developed. Six organophosphorous pesticides (OPPs) (triethylphosphorothioate, thionazin, sulfotep, phorate, disulfoton, methyl parathion and ethyl parathion) were used as model compounds and extracted from 10-mL wastewater with a binary-solvent (toluene:hexane, 1:1) mixture. Some important extraction parameters, such as extraction time, effect of salt, sample pH and solvent ratio composition were optimized. BN-LPME combined with gas chromatography/mass spectrometric (GC/MS) analysis provided repeatability (R.S.D.s ≤ 12%, n = 4), and linearity (r ≤ 0.994) and solid-phase microextraction provides comparable of R.S.D.s ≤ 13%, n = 4 and linearity (r = ≤0.966) for spiked water samples. The limits of detection (LODs) were in the range of 0.3–11.4 ng L−1 for BN-LPME and 3.1–120.5 ng L−1 for SPME at (S/N = 3) under GC/MS selective ion monitoring mode. In addition to high enrichment, BN-LPME also served as a sample cleanup procedure, with the HFM act as a filtering medium to prevent large particles and extraneous materials from being extracted. To investigate and compare their applicability, the BN-LPME and SPME procedures were applied to the detection of OPPs in domestic wastewater samples.
Co-reporter:Hoi Sim Nancy Lee, Mui Tiang Sng, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2007 Volume 1148(Issue 1) pp:8-15
Publication Date(Web):27 April 2007
DOI:10.1016/j.chroma.2007.02.104
Hollow fibre-protected liquid-phase microextraction (HF-LPME) together with gas chromatography/mass spectrometry was investigated for the analysis of degradation products of chemical warfare agents in water samples. The degradation products studied were those of nerve and blister agents, and a psychotomimetic agent. Extractions were successfully performed coupled with in-situ derivatisation using a mixture of solvent and derivatising agent. The protection of the moisture-sensitive derivatising agent was afforded by the hollow fibre. Parameters such as extraction solvent, pH, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The linear range established was between 0.005 and 5 μg ml−1 depending on analyte, with squared regression coefficients ranging from 0.9929 to 1.0000. Relative standard deviations ranged from 9% to 22%. As compared to those of solid-phase microextraction, the limits of detection (0.01–0.54 μg l−1) of the newly-developed approach were significantly improved.
Co-reporter:Chanbasha Basheer, Muthalagu Vetrichelvan, Suresh Valiyaveettil, Hian Kee Lee
Journal of Chromatography A 2007 Volume 1139(Issue 2) pp:157-164
Publication Date(Web):19 January 2007
DOI:10.1016/j.chroma.2006.11.008
Porous polypropylene hollow fiber membrane coated with a conjugated polymer was used as an on-site sampling device for the extraction of polychlorinated biphenyls and polybrominated biphenyl ethers from coastal sea water samples. The coated hollow fiber membrane was placed in a vial containing the sample, and the target compounds extracted via manual shaking of the vials at the site of sample collection. For each extraction, two fibers were used. After extraction, the fibers with the adsorbed analytes were brought back to the laboratory for further processing. Care was taken to preserve the integrity of the analytes and to avoid contamination during transport; after extraction, the fibers were carefully removed and placed in air-tight crimper vials which were stored in an ice-box. The analytes were desorbed by solvent in the laboratory and analyses were carried out using gas chromatography/mass spectrometry. This method was highly reproducible with relative standard deviations in the range of 1–9%. Recoveries from spiked water samples ranged from 83% to 98%. Low limits of detections between 0.04 and 0.21 ng l−1 were achieved. The extraction efficiency was compared with solid-phase microextraction.
Co-reporter:Yi He, Hian Kee Lee
Journal of Chromatography A 2006 Volume 1122(1–2) pp:7-12
Publication Date(Web):28 July 2006
DOI:10.1016/j.chroma.2006.04.078
Continuous flow microextraction (CFME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection has been applied to the analysis of five widely used pesticides, simazine, fensulfothion, etridiazole, mepronil and bensulide, present at trace levels in water samples. CFME employs a single organic solvent drop positioned at the tip of a polyether ether ketone (PEEK) tubing, which is immersed in a continuous flowing aqueous sample solution in a 0.5-ml glass chamber. The PEEK tubing acts as the organic drop holder and fluid delivery duct. Analytes are partitioned between the organic drop and the bulk sample solution. Important extraction factors including type of solvent, its volume, sample solution flow rate, extraction time, its pH and addition of salt were investigated. All pesticides exhibit good linearity in the investigated concentration range of 25–250 ng ml−1 with coefficients of determination (R2) ranging from 0.9879 to 0.9999 under the optimized conditions. Detection limits lower than 4 ng ml−1 were obtained for all analytes. The method was evaluated by analyzing natural water sample collected from a reservoir in Singapore. This study for the first time demonstrated the compatibility of CFME procedure and HPLC separation.
Co-reporter:Hoi Sim Nancy Lee, Chanbasha Basheer, Hian Kee Lee
Journal of Chromatography A 2006 Volume 1124(1–2) pp:91-96
Publication Date(Web):18 August 2006
DOI:10.1016/j.chroma.2006.05.030
A simple and solvent-minimised sample preparation technique based on hollow fibre-protected liquid-phase microextraction was investigated for the gas chromatography/mass spectrometric analysis of chemical warfare agents in water and slurry samples. The chemical warfare agents included four nerve agents and a blister agent. Parameters such as extraction solvent, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The technique provided a linear range of two orders of magnitude, good repeatability (RSDs < 10%, n = 6), good linearity (r2 ≥ 0.995) and limits of detection (LODs) in the range of 0.02–0.09 μg l−1 (S/N = 3) under full scan mode. The optimised technique was also applied to more complex slurry samples and similar precision (RSD < 15%, n = 3) and limits of detection (0.02–0.2 μg l−1, S/N = 3) were obtained.
Co-reporter:Chanbasha Basheer, Sindhu Swaminathan, Hian Kee Lee and Suresh Valiyaveettil
Chemical Communications 2005 (Issue 3) pp:409-410
Publication Date(Web):01 Dec 2004
DOI:10.1039/B414429E
An efficient oxidation of glucose to gluconic acid was performed using a porous gold(0) catalyst in a low-cost microreactor designed from Pyrex glass capillary tubing; compared with the conventional synthesis procedure this novel approach of using a capillary-microreactor offers a convenient and highly efficient means to optimise reaction conditions and catalytic activities.
Co-reporter:Chanbasha Basheer, Jeffrey Philip Obbard, Hian Kee Lee
Journal of Chromatography A 2005 Volume 1068(Issue 2) pp:221-228
Publication Date(Web):18 March 2005
DOI:10.1016/j.chroma.2005.01.099
A simple and novel analytical method for quantifying persistent organic pollutants (POPs) in marine sediments has been developed using microwave assisted solvent extraction (MASE) and liquid-phase microextraction (LPME) using hollow fibre membrane (HFM). POPs studied included twelve organochlorine pesticides (OCP) and eight polychlorinated biphenyl (PCB) congeners. MASE was used for the extraction of POPs from 1 g of sediment using 10 ml of ultrapure water at 600 W for 20 min at 80 °C. The extract was subsequently subjected to a single step LPME–HFM cleanup and enrichment procedure. Recovery varied between 73 and 111% for OCPs; and 86–110% for PCBs, and exceeded levels achieved for conventional multi-step Soxhlet extraction coupled with solid-phase extraction. The method detection limit for each POP analyte ranged from 0.07 to 0.70 ng g−1, and peak areas were proportional to analyte concentrations in the range of 5–500 ng g−1. Relative standard deviations of less than 20% was obtained, based on triplicate sample analysis. The optimized technique was successfully applied to POP analysis of marine sediments collected from the northeastern and southwestern areas of Singapore's coastal environment.
Co-reporter:Chanbasha Basheer, Hian Kee Lee, Jeffrey Philip Obbard
Journal of Chromatography A 2004 Volume 1022(1–2) pp:161-169
Publication Date(Web):2 January 2004
DOI:10.1016/j.chroma.2003.09.043
This study investigated the feasibility of applying liquid-phase microextraction combined with gas chromatography–mass spectrometry (GC–MS) to determine polychlorinated biphenyls (PCBs) in blood plasma. An efficient and simple extraction technique has been developed for the enrichment of PCBs from human blood plasma samples using single-step liquid-phase microextraction (LPME) in conjunction with a hollow fibre membrane (HFM). An eight PCB congener mixture was spiked into 2.5 ml of blood plasma, and the solution was then adjusted to pH 10.5 with a salinity of 20% (w/v) prior to making the total volume to 5 ml with ultrapure water. The porous HFM, filled with 3 μl of organic solvent, was then immersed into the solution, which was continuously agitated at 700 rpm for 30 min. Extract (1 μl) containing the pre-concentrated analytes was then injected into a GC–MS without further pre-treatment. Using an optimised extraction procedure, a large enrichment factor of the analytes, i.e. up to 241-fold was achieved in 30 min. The procedure resulted in a relative standard deviation of <11% (n=6), and a linear calibration range from 2.5 to 150 μg/l (r>0.999), and detection limits between 0.07 and 0.94 μg/l, respectively. To demonstrate the feasibility of the procedure, PCB concentrations were determined in actual blood samples collected from the local population in Singapore using the optimised LPME technique.
Co-reporter:Chanbasha Basheer, Rajasekhar Balasubramanian, Hian Kee Lee
Journal of Chromatography A 2003 Volume 1016(Issue 1) pp:11-20
Publication Date(Web):17 October 2003
DOI:10.1016/S0021-9673(03)01295-0
A simple and rapid liquid-phase microextraction (LPME) method using a hollow fiber membrane (HFM) in conjunction with gas chromatography–mass spectrometry (GC–MS) is presented for the quantitative determination of 16 polycyclic aromatic hydrocarbons (PAHs) and 12 organochlorine pesticides (OCPs) in rainwater samples. The LPME conditions were optimized for achieving high enrichment of the analytes from aqueous samples, in terms of hollow fiber exposure time, stirring rate, sample pH, and composition. Enrichment factors of more than 100 could be achieved within 35 min of extraction with relative standard deviations (R.S.D.s) 1.3–13.6% for PAHs and 1.7–13.8% for OCPs, respectively, over a wide range of analyte concentrations. Detection limits ranged from 0.002 to 0.047 μg l−1 for PAHs, and from 0.013 to 0.059 μg l−1 for OCPs, respectively. The newly developed LPME–GC–MS method has been validated for the analysis of PAHs and OCPs in rainwater samples. Extraction recoveries from spiked synthetic rainwater samples varied from 73 to 115% for PAHs and from 75 to 113% for OCPs, respectively. Real rainwater samples were analyzed using the optimized method. The concentrations of PAHs and OCPs in real rainwater samples were between 0.005–0.162, and 0.063 μg l−1, respectively.
Co-reporter:Yinhan Gong
Journal of Separation Science 2003 Volume 26(Issue 6‐7) pp:515-520
Publication Date(Web):9 MAY 2003
DOI:10.1002/jssc.200390069
Naphthylcarbamate-substituted (3-(2-O-β-cyclodextrin)-2-hydroxypropoxy)-propylsilyl-appended silica gel (NSCD-HPS) has been synthesized via a convenient liquid-solid phase reaction on a silica gel surface. The chromatographic behavior of NSCD-HPS in high-performance liquid chromatography (HPLC) was studied with several disubstituted benzenes and some chiral aromatic compounds under both normal and reversed-phase conditions. The results show that NSCD-HPS has excellent selectivity for the separation of positional isomers of disubstituted benzenes and enantiomers of chiral aromatic compounds.
Co-reporter:Chanbasha Basheer, Hian Kee Lee, Jeffrey Philip Obbard
Journal of Chromatography A 2002 Volume 968(1–2) pp:191-199
Publication Date(Web):30 August 2002
DOI:10.1016/S0021-9673(02)00793-8
The use of hollow fibre membrane microextraction in analytical chemistry has been increasing as the technique is a simple and efficient method for the extraction of trace organic compounds from environmental matrices. A simple liquid-phase microextraction technique using a hollow fibre membrane in conjunction with gas chromatography–mass spectrometry has been developed for the extraction and analysis of organochlorine pesticides (OCPs), i.e. α-hexachlorocyclohexane (BHC), lindane, β-BHC, heptachlor, aldrin, dieldrin, endrin, endosulfan, p,p′-DDD, p,p′-DDT, endrin aldehyde and methoxychlor, from seawater. The technique requires minimal sample preparation time and solvent consumption, and represents a significant advantage over conventional analytical methods. Optimum extraction conditions have been evaluated with respect to sample pH, salt content and stirring rate, as well as solvent type and extraction time. A high level of detection linearity (coefficient of >0.9995, less than 14% RSD) was obtained for OCPs over a range of analyte concentrations between 5 and 100 μg l−1, with detection limits in the parts per trillion (ppt) to sub-parts per billion range. Comparison between liquid-phase microextraction with hollow fibre membrane and US Environmental Protection Agency Method 508 showed that the novel method has comparable detection limits of between 0.013 and 0.059 μg l−1 in seawater.
Co-reporter:Lei Sun
Journal of Separation Science 2002 Volume 25(Issue 1‐2) pp:67-76
Publication Date(Web):24 JAN 2002
DOI:10.1002/1615-9314(20020101)25:1/2<67::AID-JSSC67>3.0.CO;2-5
Microwave-Assisted extraction (MAE) was applied for the first time to study the thermal degradation of five carbamates (propoxur, thiuram, propham, methiocarb, chlorpropham) after heating for 6 min at 95°C with different extractants. Analytes were determined by high performance liquid chromatography (HPLC) with UV detection. It was found that significant thermal degradation of the five targets occurred under the extraction conditions. The break down percentage ranged from 10% to 100%, depending on polarities of both analytes and extractants. The greater the polarity of the extractant, the less degradation the analyte underwent. Lower recoveries were found for all carbamates with less polar extractants, such as hexane-acetone (4 : 1, v/v) and dichloromethane. With more polar extractants (methanol, hexane-acetone 1 : 4 and 1 : 1), higher recoveries of three carbamates (propoxur, methiocarb, and chlorpropham) were obtained, whereas the recoveries of the other two remained low. Some non-polar and polar pollutants spiked in soil, such as polynuclear aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs), triazines (atrazine, simazine), and carbamates (propoxur, methiocarb, chlorpropham), subjected to MAE in a closed-vessel microwave system under 80% magnetron power output (1 200 W) at 115°C, were also studied. The recoveries of such pollutants ranged between 70% and 99% with excellent reproducibility, except for carbamates. The effects of the soil matrix, the soil moisture, and aging on recoveries were also investigated.
Co-reporter:Su Yin Tham;Lingyan Zhu;Adrian U. J. Yap
Journal of Separation Science 2002 Volume 25(Issue 5‐6) pp:328-332
Publication Date(Web):11 APR 2002
DOI:10.1002/1615-9314(20020401)25:5/6<328::AID-JSSC328>3.0.CO;2-1
The release of fluoride is an important factor in evaluating a composite restorative material due to its anticariogenic effect. Field amplified stacking injection in capillary electrophoresis was studied to determine the concentration of fluoride released from dental restorative materials. A detection limit of 20 ng/mL was obtained with good reproducibility (relative standard deviation < 4%). The method was applied to the analysis of fluoride released from four different types of commercially available dental composites over 28 days. Results showed that field-amplified stacking injection-capillary electrophoresis was effective in monitoring the fluoride release process and product quality of different kinds of restorative materials.
Co-reporter:Yinhan Gong;Hian Kee Lee
Helvetica Chimica Acta 2002 Volume 85(Issue 10) pp:3283-3293
Publication Date(Web):7 NOV 2002
DOI:10.1002/1522-2675(200210)85:10<3283::AID-HLCA3283>3.0.CO;2-H
Two novel types of crown ether capped β-cyclodextrin (β-CD) bonded silica, namely, 4′-aminobenzo-X-crown-Y (X=15, 18 and Y=5, 6, resp.) capped [3-(2-O-β-cyclodextrin)-2-hydroxypropoxy] propylsilyl-appended silica, have been prepared and used as stationary phases in capillary electrochromatography (CEC) to separate chiral compounds. The two stationary phases have a chiral selector with two recognition sites: crown ether and β-CD. They exhibit excellent enantioselectivity in CEC for a wide range of compounds. After inclusion of metal ions (Na+ or K+) from the running buffer into the crown ether units, the stationary phases become positively charged and can provide extra electrostatic interaction with ionizable solutes and enhance the dipolar interaction with polar neutral solutes. This enhances the host-guest interaction with the solute and improves chiral recognition and enantioselectivity. Due to the cooperation of the anchored β-CD and the crown ether, this kind of crown ether capped β-CD bonded phase shows better enantioselectivity than either β-CD- or crown ether bonded phases only. These new types of stationary phases have good potential for fast chiral separation with CEC.
Co-reporter:Sini George and Hian Kee Lee
Analytical Methods (2009-Present) 2010 - vol. 2(Issue 4) pp:NaN334-334
Publication Date(Web):2010/02/02
DOI:10.1039/B9AY00300B
A nanocomposite was prepared using single walled carbon nanotubes (SWCNTs) and thiol-derivatised gold nanoparticles (Aunano). Transmission electron microscopy (TEM) image of the nanocomposite showed that the Aunano were self-assembled on to the side walls of the SWCNTs after the modification process. Moreover, from the TEM analysis, it was clear that the likelihood of agglomeration of these nanoparticles in the nanocomposite were rare. A film of the nanocomposite was then applied on a glassy carbon electrode (GCE). The nanocomposite modified GCE was used for the electrochemical detection of several carcinogenic polycyclic aromatic amines (PAAs) simultaneously. The combination of the adsorptive properties of SWCNTs with an enhanced electroactive surface area, electrical conductivity of Aunano, together with the interaction of the amino group of the analytes and Aunano permitted very efficient detection of the analytes. Preconcentration and detection of the analytes in the real samples could be achieved in a single step using adsorptive stripping voltammetry (ASV). ASV for the PAAs achieved detection limits in the range of 1 μg L−1 (using 9,10-diaminophenanthrene as an example), with linearity up to 3 orders of magnitude. Moreover, the nanocomposite modified electrode exhibited excellent selectivity with high reproducibility towards several PAAs and resulted in their simultaneous and sensitive detection with detection limits in the μg L−1 range. Using 9,10-diaminophenanthrene as an example, the reproducibility of the analyte signal in the simultaneous detection of several PAAs was determined to be within 5% (n = 8) from one electrode preparation to another, and the response signal was stable (±4.5% at 95% confidence interval) for 15 repeated analyses with 600 s of preconditioning. Applicability of the procedure to tap water, river water, and wastewater samples was demonstrated. Such nanocomposite devices hold great promise for convenient and sensitive environmental screening of carcinogenic PAAs.
