To improve repeatability and efficiency and to simplify the operation procedure of capillary electrophoresis (CE), a pressurized CE system (p-CE) with injection valve sampling was developed. It consisted of one high-pressure pump, a six-port injection valve, a PEEK cross, a separation and back pressure capillary, an ultraviolet-visible detector and a high voltage power supply. The pressure-driven flow ranging from 4.5 nL min−1 to 0.81 μL min−1 in the separation capillary was produced by splitting to the flow from the high-pressure pumps (0.005–0.4 mL min−1). Nano-volume sample injection (<10 nL) was conducted by a micro-volume rotary injector (0.5–5 μL) with flow splitting. In the p-CE system, the new commercial capillary could be directly used without any wash, and the capillary-flush process between runs was also eliminated. In this case, the analytes were driven toward the outlet of the separation capillary by the pressurized flow, the electric field force and minute electroosmotic flow, and they were separated owing to the electrophoretic mobility. The p-CE system allows for the independent variation of the pressurized flow rate and electrical field and electrophoretic separation of good repeatability (below 3%) under high electrical fields (500–1000 V cm−1) and flow rate gradient modes. The feasibility of the p-CE system in real analysis was demonstrated by iodate quantification in iodized table salts. The separation of iodide and iodate was realized within 0.3 min, proving its high analytical speed.

•Baseline separation was achieved by adding an ion-pairing reagent (TBAH).•Resolution improvement resulted from the electrostatic interaction between TBAH and negatively charged iodine species.•Rapid separation of four iodine species was obtained within 7.0 min.•Iodine speciation in seaweed was analyzed.This study achieved resolution improvement for iodine speciation in the presence of an ion-pairing reagent by a pressure-driven capillary electrophoresis (CE) system. Addition of 0.01 mM tetrabutyl ammonium hydroxide (TBAH) as the ion-pairing reagent into the electrophoretic buffer resulted in the complete separation of four iodine species (I−, IO3−, mono-iodothyrosine-MIT and di-iodothyrosine-DIT), because of the electrostatic interaction between TBAH and the negatively charged analytes. A +16 kV separation voltage was applied along the separation capillary (50 μm i.d., 80 cm total and 60 cm effective) with the inlet grounded. The detection wavelength was fixed at 210 nm, and the pressure-driven flow rate was set at 0.12 mL min−1 with an injected volume of 2 μL. The optimal electrolyte consisted of 2 mM borate, 2 mM TBAH and 80% methanol with pH adjusted to 8.5. Baseline separation of iodine species was achieved within 7 min. The detection limits for I−, IO3−, MIT and DIT were 0.052, 0.040, 0.032 and 0.025 mg L−1, respectively. The relative standard deviations of peak heights and areas were all below 3% for 5 mg L−1 and 5% for 1 mg L−1. Application of the proposed method was demonstrated by speciation analysis of iodine in two seaweed samples. The developed method offered satisfactory recoveries in the 91–99% range and good precisions (<5%). Good agreement between the determined values by the proposed CE method and the HPLC-ICP-MS method was also obtained. All results proved its great potential in routine analysis of iodine speciation in environmental, food and biological samples.

For direct analyses of micro-samples and the hyphenation with nanoflow separation techniques, a low-cost demountable nanoflow nebulizer was fabricated for inductively coupled plasma mass spectrometry (ICP-MS). A small-bore capillary (20 μm) with a tapered tip served as the sample capillary of the nebulizer. The gas orifice diameter, the internal diameter and the wall thickness at the tip of the sample capillary were 160, 20, and 5 μm, respectively, which ensured stable generation of aerosol by the nebulizer at nanoflow rates down to 50 nL min−1 and an ultra-low aspiration rate (80 nL min−1). Narrower aerosol size distribution and higher analyte transport efficiency (nearly 100%) were obtained with the proposed nebulizer than with the previous demountable capillary microflow nebulizer. The sensitivity and detection limit of the proposed nebulizer at 500 nL min−1 were about one third of those obtained by using the demountable capillary microflow nebulizer at 5 μL min−1, whereas the precision of the former at 500 nL min−1 was even to some extent superior over that obtained with the latter at 5 μL min−1. Furthermore, the ICP-MS instrument could tolerate direct introduction of 100% organic solvents by using the developed nebulizer operating at nanoflow rates. It was utilized to sheathless interface nano-high performance liquid chromatography with ICP-MS for arsenic speciation analysis with good accuracy and precision, proving its strong robustness and good suitability.

In this work, we report a rapid analytical method for the determination of trace formaldehyde in cosmetics on a 12.5 mm C18 guard column. The shortest time (0.5 min) was obtained for one separation with 1.5 mL min−1 of methanol–water 50:50 (v/v) as the mobile phase at a column temperature of 30 °C. A linear response between peak area and the concentration of formaldehyde was obtained over the range 0.1 to 20 mg L−1 with a relative standard deviation of 1.4% (n = 10) at the concentration of 1.0 mg L−1 and a detection limit of 5.1 μg L−1. The confirmation assay by liquid chromatography tandem mass spectrometry indicated that there was no interfering effect from other carbonyl compounds. The proposed method was applied for the determination of formaldehyde residue in cosmetics at the mg L−1 level. Free formaldehyde up to 27 mg kg−1 was found in cosmetics and the spike recovery at the spiked levels of 1.0 and 10.0 mg L−1 varying from 92% to 105% was also obtained. The difference between the values determined by the proposed method and the standard spectrophotometric method was below 3.7%. The results proved the accuracy and precision of the method, showing potential for the routine analysis of formaldehyde residue.

A sensitive method for the quantification of acequinocyl and hydroxyacequinocyl in foodstuff (beef, chicken muscle and liver, fish, peach, cucumber, Chinese cabbage and broad bean) was developed by ultra-high performance liquid chromatography and tandem mass spectrometry. Acequinocyl and hydroxyacequinocyl were found to be stable in the presence of formic acid at low temperature (−18 °C) in the dark. The target compounds in solid food samples were successively extracted by acetonitrile containing 0.5 % (v/v) formic acid, and then cleaned up by using Florisil columns, and then evaporated to near dryness under a nitrogen stream at 40 °C, and finally dissolved in acetonitrile containing 0.5 % (v/v) formic acid. No matrix effect was observed from any foodstuff. Linear calibration curves with correlation coefficients of 0.9996 for acequinocyl and 0.9998 for hydroxyacequinocyl over the same range 2 to 100 μg L−1 were obtained. The intra-day and inter-day relative standard deviations were both superior to 3 % (N = 10) for 5 μg L−1. The method detection limits were 1.4 μg kg−1 for acequinocyl and 1.3 μg kg−1 for hydroxyacequinocyl. The method quantification limits were 4.6 and 4.3 μg kg−1, respectively, which were at least five times lower than their maximum residue limits for food. Neither acequinocyl nor hydroxyacequinocyl was detected in any foodstuff. The recoveries at spiked levels of 5, 10, and 50 μg kg−1 varied in the ranges 81–100 % for acequinocyl and 77–103 % for hydroxyacequinocyl in the foodstuffs, validating the accuracy of the proposed method.

•Hg+, MeHg, EtHg and Hg2+ were enriched by the SAX column preconditioned with sodium 3-mercapto-1-propanesulfonate.•The enrichment factors of 1025–1108 were obtained using 6 mL sample in a 1.5-min enrichment procedure.•Rapid separation was achieved within 5 min on a 50-mm C18 column using 0.5% (v/v) 2-mercaptoethanol as the mobile phase.•MeHg, EtHg and Hg2+ concentrations at sub ng L−1 to sub μg L−1 levels were detected in the water.A hyphenated method for mercury speciation analysis by the coupling of high performance liquid chromatography and inductively coupled plasma mass spectrometry with the online strong anion exchange column (SAX) preconcentration was developed. The Hg analytes (Hg+, MeHg, EtHg and Hg2+) were absorbed on the SAX column preconditioned with sodium 3-mercapto-1-propanesulfonate, and then rapidly eluted (less than 16 s) by 5 μL 3% (v/v) 2-mercaptoethanol. The enrichment factors of 1025 for Hg+, 1084 for MeHg, 1108 for EtHg and 1046 for Hg2+ were obtained using 6 mL sample in a 1.5-min enrichment procedure. Rapid separation of the four mercurial compounds was achieved within 5 min on a 50-mm C18 column using 0.5% (v/v) 2-mercaptoethanol as the mobile phase. The detection limits for Hg+, MeHg, EtHg and Hg2+ were 0.015, 0.010, 0.009 and 0.016 ng L−1, each, and the relative standard deviations of peak height and peak area (5 ng L−1 for each Hg species) were all below 5%. Mercury speciation in three freshwater, two drinking water and two seawater samples were then analyzed by the proposed method. MeHg and Hg2+ concentrations down to 0.14 and 0.56 ng L−1 were detected in the drinking waters.This work demonstrated the online mercury preconcentration by a strong anion exchange guard column, followed by high performance liquid chromatographic separation and inductively coupled plasma mass spectrometry detection. The mercury species were enriched by around 1000-fold using 6 mL sample in a 1.5-min enrichment procedure.

This work described the utilization of ion-pair reversed phase liquid chromatography coupled to inductively coupled plasma mass spectrometry (RP-LC-ICP-MS) for iodine speciation analysis in urine. Considering the requirements of green analytical chemistry and the Ar ICP-MS instrument, three aqueous mobile phases were employed for the separation of seven iodine species including iodide, iodate and five iodo amino acids (monoiodotyrosine – MIT, di-iodotyrosine – DIT, tri-iodothyronine – T3, reversed tri-iodothyronine – rT3, and thyroxine – T4). The aqueous mobile phases were composed of an ion-pair reagent (tetrabutylammonium hydroxide – TBAH) and an eluent (ammonium chloride, L-phenylalanine or deoxycholic acid) at low concentrations in ultrapure water. Owing to tremendous difference in retention behavior between these iodinated forms, a gradient elution mode was performed for the rapid separation of IO3− and I−, MIT and DIT, and T3, rT3 and T4, respectively. Iodine species separation was achieved with a 12.5 mm C18 guard column in 7 min. The detection limits for IO3−, I−, MIT, DIT, T3, rT3 and T4 were 0.047, 0.046, 0.057, 0.072, 0.093, 0.094 and 0.081 μg L−1, respectively. Application of the proposed method was demonstrated by the speciation analysis of iodine in four real urine samples. The developed method offered satisfactory recoveries in the 93–106% range and good repeatability, showing great potential in routine analysis of iodine speciation in environmental, food and biological samples.

•Four mercurial forms were separated via a 12.5-mm strong anion exchange column by complexing with 3-mercapto-1-propanesulfonate into negatively charged complexes.•The fastest analysis of mercury speciation in 5.0 min was obtained so far.•The most environment-friendly mobile phase (1.0 mM sodium 3-mercapto-1-propanesulfonate at pH 7.0) was employed.•Mercurial species in fish was determined by the proposed AEC–ICP-MS method.This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg2+), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg2+, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L−1, respectively. The relative standard deviations of peak height and peak area (5.0 μg L−1 for each Hg species) were all below 3%. The determined contents of Hg2+, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.

•Hg2+, MeHg, EtHg and PhHg were separated on two sequential 12.5-mm SCX columns.•The shortest separation time (2–2.5 min) was consumed.•The mobile phase was most environment-friendly and fairly compatible with ICP-MS.In this work, a hybrid method for the rapid speciation of mercury compounds by cation exchange chromatographic separation and inductively coupled plasma mass spectrometry (ICP-MS) detection is reported. Effective separation of inorganic mercury (Hg2+), methylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) within 2–2.5 min was achieved on two consecutive 12.5-mm strong cation exchange guard columns with 2.0 mM l-cysteine or thiourea (pH 2.0) as the mobile phase. This separation met the requirements of green analytical chemistry such as the prevention of toxic waste, safer HPLC mobile phases, and short separation times to reduce operating costs. The detection limits for Hg2+, MeHg, EtHg and PhHg were 0.019, 0.027, 0.031 and 0.022 μg L−1, each, and the repeatabilities of peak height and peak area (5.0 μg L−1 for each Hg species) were all lower than 3%. Contents of Hg species and total mercury in certified reference materials of seawater (GBW(E) 080042) and fish tissue (GBW 10029) were in good accordance with the certified values, and satisfactory recoveries (96–102% for GBW(E) 080042 and 94–101% for GBW 10029) validated the developed method. The developed method was applied for the speciation of mercury in five seawater sample and five marine fish samples. The concentrations of mercury species in all analyzed fish samples did not exceed the permissible levels of the National Standard of China.

A microfluidic chip-based nanoflow injection system was set up for inductively coupled plasma mass spectrometry (ICP-MS). The sample plug loaded into the sampling channel of the microchip was driven into ICP-MS, as soon as the multi-functional valve was changed from the load position to the inject position. The sample plug shape depends on the sampling channel. 40–200 nL sample was introduced into ICP-MS with 5–25 mm sampling channel. The proposed microchip-based nanoflow injection sampling system offers many advantages such as low sample consumption, satisfactory precisions (less than 3.0%), low sampling dead volume (nearly zero) and easy fabrication etc. With 200-nL sampling volume and a flow rate of 20 μL min−1 for the carrier, a peak profile with the highest peak height within the shortest time was obtained. The absolute detection limit of the chip-based nanoflow injection sampling system for 195Pt was 2.54 fg under the optimized conditions, which was improved by a factor of 3200 in comparison with the conventional sampling system. A sample throughput of 48 h−1 was obtained with the nanoflow injection sampling system. Relative standard deviations of peak heights of 10 replicate trials of 10 μg L−1 standard solution and the human plasma sample S1 were 1.71% and 2.65%, respectively. The contents of platinum in six human plasma samples detected by the proposed method agreed well with those by the conventional sampling system, and the recoveries of six plasma samples ranged from 94.3% to 103.0%. These results indicate the good accuracy of the present method.A microchip-based nanoflow injection system was used for the analysis of limited biological samples by inductively coupled plasma mass spectrometry, which offers outstanding advantages including low sample consumption (50–200 nL), satisfactory precisions, low sampling dead volume (nearly zero) and easy fabrication.

For direct analyses of micro-samples and the hyphenation with nanoflow separation techniques, a low-cost demountable nanoflow nebulizer was fabricated for inductively coupled plasma mass spectrometry (ICP-MS). A small-bore capillary (20 μm) with a tapered tip served as the sample capillary of the nebulizer. The gas orifice diameter, the internal diameter and the wall thickness at the tip of the sample capillary were 160, 20, and 5 μm, respectively, which ensured stable generation of aerosol by the nebulizer at nanoflow rates down to 50 nL min−1 and an ultra-low aspiration rate (80 nL min−1). Narrower aerosol size distribution and higher analyte transport efficiency (nearly 100%) were obtained with the proposed nebulizer than with the previous demountable capillary microflow nebulizer. The sensitivity and detection limit of the proposed nebulizer at 500 nL min−1 were about one third of those obtained by using the demountable capillary microflow nebulizer at 5 μL min−1, whereas the precision of the former at 500 nL min−1 was even to some extent superior over that obtained with the latter at 5 μL min−1. Furthermore, the ICP-MS instrument could tolerate direct introduction of 100% organic solvents by using the developed nebulizer operating at nanoflow rates. It was utilized to sheathless interface nano-high performance liquid chromatography with ICP-MS for arsenic speciation analysis with good accuracy and precision, proving its strong robustness and good suitability.

This work described the utilization of ion-pair reversed phase liquid chromatography coupled to inductively coupled plasma mass spectrometry (RP-LC-ICP-MS) for iodine speciation analysis in urine. Considering the requirements of green analytical chemistry and the Ar ICP-MS instrument, three aqueous mobile phases were employed for the separation of seven iodine species including iodide, iodate and five iodo amino acids (monoiodotyrosine – MIT, di-iodotyrosine – DIT, tri-iodothyronine – T3, reversed tri-iodothyronine – rT3, and thyroxine – T4). The aqueous mobile phases were composed of an ion-pair reagent (tetrabutylammonium hydroxide – TBAH) and an eluent (ammonium chloride, L-phenylalanine or deoxycholic acid) at low concentrations in ultrapure water. Owing to tremendous difference in retention behavior between these iodinated forms, a gradient elution mode was performed for the rapid separation of IO3− and I−, MIT and DIT, and T3, rT3 and T4, respectively. Iodine species separation was achieved with a 12.5 mm C18 guard column in 7 min. The detection limits for IO3−, I−, MIT, DIT, T3, rT3 and T4 were 0.047, 0.046, 0.057, 0.072, 0.093, 0.094 and 0.081 μg L−1, respectively. Application of the proposed method was demonstrated by the speciation analysis of iodine in four real urine samples. The developed method offered satisfactory recoveries in the 93–106% range and good repeatability, showing great potential in routine analysis of iodine speciation in environmental, food and biological samples.