Co-reporter:Chuang Chen, Hong Chen, and Haiyang Li
Analytical Chemistry December 19, 2017 Volume 89(Issue 24) pp:13398-13398
Publication Date(Web):November 30, 2017
DOI:10.1021/acs.analchem.7b03629
Ion gate is a key buildup for drift tube ion mobility spectrometry (IMS) and its combination with mass spectrometry. Bradbury–Nielsen gate, as the most commonly used ion gate in IMS, possesses a distinct ion mobility discrimination effect due to its depletion features. This impedes the scaling of the ion gate opening time to improve the separation capability of IMS while keeping its sensitivity for multiple ion species. In this work, a Tyndall–Powell gate (TPG) simply composed of two identical wire grids was used to develop an ion gate with nearly no ion mobility discrimination for IMS. Experimental results showed that the TPG features a gate region where the electric field for opening the gate could be enhanced to effectively solve the ion mobility discrimination problem related to it. Meanwhile, enhancing that electric field enabled the TPG-IMS to keep a resolving power over 106 at 100 °C for ion peak with a signal-to-noise ratio up to 800. With that TPG-IMS, baseline separation of two ion peaks, the hydronium and the acetone monomer peaks with a reduced mobility difference of only 0.04 cm2 V–1 s–1, was achieved with no sensitivity loss for the least mobile acetone dimer ions.
Co-reporter:Wei Huang, Weiguo Wang, Chuang Chen, Mei Li, Liying Peng, Hang Li, Jiwei Liu, Keyong Hou, Haiyang Li
Talanta 2017 Volume 175(Volume 175) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.talanta.2017.07.076
•Ion mobility spectrometry was developed to monitor gaseous ammonia in the ambient air in a long-term measurement.•The quantitative analysis frequency has achieved 10 Hz with a data averaging of 10 times.•The limit of detection of sub-ppb level was obtained.•The affect of ambient humidity was greatly reduced using drift temperature of over 150 °C.A real-time dynamic measurements of ammonia (NH3) is crucial for understanding the atmospheric nucleation process. A novel method was developed for on line monitoring at the sub-second time scale for the gaseous ammonia in ambient air for months, based on a positive inhaling ion mobility spectrometry (IMS) with a 63Ni ion source. The selective detection of NH3 was achieved using a high resolution IMS with an optimization of the drift tube temperature above 150 °C. This method improved the peak-to-peak resolution significantly, thus avoided the interferences of the adjacent peaks to the quantitative analysis of NH3. The time resolution of the IMS was less than 0.1 s at a data averaging of 10 times. The limit of detection (LOD) achieved at sub-ppb level while a linear response of peak intensity versus concentration of NH3 in the range of 10–60 ppb and 60–400 ppb were obtained. The relative standard deviations (RSD), the confidence level and the errors were 1.06%, 95% and ± 0.21 ppb by measuring 100 ppb NH3 for 100 times. The effect of ambient humidity could be greatly reduced by using the drift temperature of over 150 °C. At last, the application of measuring the NH3 concentration evolutions of Dalian city was performed from June 19 to December 3 in 2015. The results illustrated a potential method of using IMS for a real-time measuring atmospheric NH3 at an unprecedented accuracy and sensitivity with long-term stability.Download high-res image (272KB)Download full-size image
Co-reporter:Shasha Cheng, Haitao Li, Dandan Jiang, Chuang Chen, Tan Zhang, Yong Li, Haitao Wang, Qinghua Zhou, Haiyang Li, Mingqian Tan
Talanta 2017 Volume 162() pp:398-402
Publication Date(Web):1 January 2017
DOI:10.1016/j.talanta.2016.10.056
•An innovated method based on dopant-assisted positive photoionization IMS was developed for trimethylamine (TMA) detection.•The influence of dopant species and drift tube temperature on TMA detection was investigated.•The LOD for the TMA was as low as 1 ppb.•TMA generated by oyster and shrimp during 4 °C storage was evaluated successfully by DAAP-IMS.Biogenic amines are degradation products generated through enzymatic and microbial processes during food spoilage, which may pose a health hazard to consumers at elevated levels. Trimethylamine (TMA) is a good target for the detection of biogenic amines due to its volatility and fishy odor. In this study, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) for rapid and sensitive detection of TMA. Response of TMA was enhanced by the addition of dopants and characteristic product ions with reduced mobility 2.26 cm2 V−1 s−1 were formed. 2-Butaone was chosen as the dopant for better separation between reagent ion peak and TMA product ion peak as well as higher sensitivity and the limit of detections (LODs) for TMA standard sample was 1 ppb. The potential application of DAAP-IMS was evaluated by the detection of TMA generated by oyster and shrimp during 4 °C storage. Analysis of two kinds of seafood showed the same characteristic peak to TMA standard sample, and the intensity of TMA increased over the storage time. The results of this study testify to the potential of DAPP-IMS for qualitative and quantitative determination of TMA in real food samples.
Photon ionization mass spectrometry (PI-MS) is a widely used technique for the online detection of trace substances in complex matrices. In this work, a new high-pressure photon ionization (HPPI) ion source based on a vacuum ultraviolet (VUV) Kr lamp was developed for time-of-flight mass spectrometry (TOFMS). The detection sensitivity was improved by elevating the ion source pressure to about 700 Pa. A radio frequency (RF)-only quadrupole was employed as the ion guide system following the HPPI source to achieve high ion transmission efficiency. In-source collision induced dissociation (CID) was conducted for accurate chemical identification by varying the voltage between the ion source and the ion guide. The high humidity of the breath air can promote the detection of some compounds with higher ionization potentials (IPs) that could not be well detected by single photon ionization (SPI) at low pressure. Under 100% relative humidity (37 °C), the limits of detection down to 0.015 ppbv (parts per billion by volume) for aliphatic and aromatic hydrocarbons were obtained. This HPPI-TOFMS system was preliminarily applied for online investigations of the exhaled breath from both healthy nonsmoker and smoker subjects, demonstrating its analytical capacity for complicated gases analysis. Subsequently, several frequently reported VOCs in the breath of healthy volunteers, i.e., acetone, isoprene, 2-butanone, ethanol, acetic acid, and isopropanol, were successfully identified and quantified.
Soft ionization mass spectrometry is one of the key techniques for rapid detection of trace volatile organic compounds. In this work, a novel photoionization-generated dibromomethane cation chemical ionization (PDCI) source has been developed for time-of-flight mass spectrometry (TOFMS). Using a commercial VUV lamp, a stable flux of CH2Br2+ was generated with 1000 ppmv dibromomethane (CH2Br2) as the reagent gas, and the analytes were further ionized by reaction with CH2Br2+ cation via charge transfer and ion association. Five typical volatile sulfur compounds (VSCs) were chosen to evaluate the performance of the new ion source. The limits of detection (LOD), 0.01 ppbv for dimethyl sulfide and allyl methyl sulfide, 0.05 ppbv for carbon disulfide and methanthiol, and 0.2 ppbv for hydrogen sulfide were obtained. Compared to direct single photon ionization (SPI), the PDCI has two distinctive advantages: first, the signal intensities were greatly enhanced, for example more than 10-fold for CH3SH and CS2; second, H2S could be measured in PDCI by formation [H2S + CH2Br2]+ adduct ion and easy to recognize. Moreover, the rapid analytical capacity of this ion source was demonstrated by analysis of trace VSCs in breath gases of healthy volunteers and sewer gases.
Peroxide explosives, such as triacetone triperoxide (TATP) and hexamethylene trioxide diamine (HMTD), were often used in the terrorist attacks due to their easy synthesis from readily starting materials. Therefore, an on-site detection method for TATP and HMTD is urgently needed. Herein, we developed a stand-alone dopant-assisted positive photoionization ion mobility spectrometry (DAPP-IMS) coupled with time-resolved thermal desorption introduction for rapid and sensitive detection of TATP and HMTD in complex matrices, such as white solids, soft drinks, and cosmetics. Acetone was chosen as the optimal dopant for better separation between reactant ion peaks and product ion peaks as well as higher sensitivity, and the limits of detection (LODs) of TATP and HMTD standard samples were 23.3 and 0.2 ng, respectively. Explosives on the sampling swab were thermally desorbed and carried into the ionization region dynamically within 10 s, and the maximum released concentration of TATP or HMTD could be time-resolved from the matrix interference owing to the different volatility. Furthermore, with the combination of the fast response thermal desorber (within 0.8 s) and the quick data acquisition software to DAPP-IMS, two-dimensional data related to drift time (TATP: 6.98 ms, K0 = 2.05 cm2 V–1 s–1; HMTD: 9.36 ms, K0 = 1.53 cm2 V–1 s–1) and desorption time was obtained for TATP and HMTD, which is beneficial for their identification in complex matrices.
Co-reporter:Weiguo Wang, Wuduo Zhao, Lei Hua, Keyong Hou, Haiyang Li
Chemical Physics Letters 2016 Volume 652() pp:239-242
Publication Date(Web):16 May 2016
DOI:10.1016/j.cplett.2016.04.052
•The different distribution patterns of multiply charged ions on polarization state is presented.•A theoretical calculation could explain the related experimental results.•The cluster disintegration should be considered for the production of multiply charged ions.This paper investigated the dependence of multiply charged ions on the laser polarization state when benzene cluster was irradiated with 532 and 1064 nm nanosecond laser. A circle, square and flower distribution for C2+, C3+ and C4+ were observed with 532 nm laser respectively, while flower petals for C2+, C3+ and C4+ were observed at 1064 nm as the laser polarization varied. A theoretical calculation was performed to interpret the polarization state and wavelength dependence of the multiply charged ions. The simulated results agreed well with the experimental observation with considering the contribution from the cluster disintegration.
Co-reporter:Liying Peng, Dandan Jiang, Zhenxin Wang, Lei Hua, Haiyang Li
Talanta 2016 Volume 153() pp:295-300
Publication Date(Web):1 June 2016
DOI:10.1016/j.talanta.2016.03.041
•An innovated method based on DANP-IMS was put forward.•Influence of moisture was effectively reduced via an on-line semiconductor cooling inlet.•LOQs for humid H2S were achieved to ≤79.0 ng L−1.•Sewer H2S content in manholes was monitored in real time and its correlation with the resident daily activities was observed.Malodorous hydrogen sulfide (H2S) gas often exists in the sewer system and associates with the problems of releasing the dangerous odor to the atmosphere and causing sewer pipe to be corroded. A simple method is in demand for real-time measuring H2S level in the sewer gas. In this paper, an innovated method based on dopant-assisted negative photoionization ion mobility spectrometry (DANP-IMS) with on-line semiconductor cooling inlet was put forward and successfully applied for the real-time measurement of H2S in sewer gas. The influence of moisture was effectively reduced via an on-line cooling method and a non-equilibrium dilution with drift gas. The limits of quantitation for the H2S in ≥60% relative humidity air could be obtained at ≤79.0 ng L−1 with linear ranges of 129–2064 ng L−1. The H2S concentration in a sewer manhole was successfully determined while its product ions were identified by an ion-mobility time-of-fight mass spectrometry. Finally, the correlation between sewer H2S concentration and the daily routines and habits of residents was investigated through hourly or real-time monitoring the variation of sewer H2S in manholes, indicating the power of this DANP-IMS method in assessing the H2S concentration in sewer system.
Co-reporter:Wei Liu, Jichun Jiang, Keyong Hou, Weiguo Wang, Yachen Qi, Yan Wang, Yuanyuan Xie, Lei Hua, Haiyang Li
Talanta 2016 Volume 161() pp:693-699
Publication Date(Web):1 December 2016
DOI:10.1016/j.talanta.2016.09.026
•An innovative soft ionization source based on windowless VUV lamp was put forward.•The attenuation of the sensitivity with conventional VUV lamp was eliminated.•An efficient automatic enrichment system for trace chlorinated benzenes was set up.•The LOQs for MCBz, DCBz and TrCBz were as low as 5.37–7.65 pptv.•The flue gas has been online monitored for three months with unattended operation.Chlorinated benzenes are typical precursors and indicators for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from waste incinerators. Online and real-time monitoring of chlorobenzenes is a challenge due to their low concentration and complex nature of the flue gas. In this work, a continuous online monitoring system was built for detection of trace chlorinated benzenes based on a time-of-flight mass spectrometer (TOFMS). A single photon ionization (SPI) source based on a radiofrequency-excited windowless vacuum ultraviolet (VUV) lamp was developed for the first time to eliminate the signal attenuation resulting from the contamination of magnesium fluoride windows and to avoid the fragment ions. An automatic enrichment system including three parallel Tenax TA adsorption tubes was designed and coupled to the TOFMS to achieve the required ultrahigh sensitivity. The limits of quantitation at 7.65, 5.37 and 6.77 pptv were obtained for monochlorobenzene (MCBz), dichlorobenzene (DCBz) and trichlorobenzene (TrCBz), respectively, within a 29-min analytical period. Moreover, this apparatus was applied to continuously online monitor the actual flue gas from a waste incinerator for three months. During this period, the concentrations of MCBz, DCBz and TrCBz detected in the flue gas were in the range of 100–1200, 50–800 and 50–300 pptv, respectively. The relative standard deviation (RSD) of the sensitivity for the windowless VUV lamp ion source was 9.71% evaluated by the internal standard benzene over the 3-months flue gas monitoring. These results demonstrated the capability of this method in long-term analysis of the trace chlorinated benzenes in the flue gas.
Journal of The American Society for Mass Spectrometry 2016 Volume 27( Issue 1) pp:144-152
Publication Date(Web):2016 January
DOI:10.1007/s13361-015-1238-3
The specific locations of the double bonds in linear olefins can facilitate olefin catalytic synthetic reactions to improve the quality of target olefin products. We developed a simple and efficient approach based on single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) combined with online ozonolysis to identify and quantify the linear olefin double bond positional isomers. The online ozonolysis cleaved the olefins at the double bond positions that led to formation of corresponding characteristic aldehydes. The aldehydes were then detected by SPI-TOFMS to achieve unique spectrometric “fingerprints” for each linear olefin to successfully identify the isomeric ones. To accurately quantify the isomeric components in olefin mixtures, an algorithm was proposed to quantify three isomeric olefin mixtures based on characteristic ion intensities and their equivalent ionization coefficients. The relative concentration errors for the olefin components were lower than 2.5% while the total analysis time was less than 2 min. These results demonstrate that the online ozonolysis SPI-TOFMS has the potential for real-time monitoring of catalytic olefin synthetic reactions.
Bradbury–Nielsen gate (BNG) is commonly used in ion mobility spectrometers. It, however, transmits only a small fraction of the ions into the drift region, typically 1%. In contrast, all ions in the ionization chamber could be efficiently compressed into the drift region by the field switching gate (FSG). We report in this paper on the simultaneous use of BNG and field switching (FS) to enhance ion utilization of the BNG. In this technique, the FS collects the ions existing in the region between the FS electrode and the BNG and drives them quickly, going through the BNG in the period of gate opening. The BNG acts as the retarding field in the reported FSG to stop ions from diffusing into the drift region in the period of gate closing. Using this technique, an increase of at least 10-fold in the ion peak height without any loss of resolution is achieved for acetone compared with the BNG-only approach at a gate pulse width of 150 μs, and an even larger improvement factor of 21 is achieved for heavier DMMP dimer ions. This technique can be adapted to the current BNG-based ion mobility instruments to significantly enhance their sensitivity without any modification of the drift tube hardware.
Single-photon ionization mass spectrometry (SPI-MS) is a versatile and powerful analytical technique for online and real-time analysis of organic species; however, it is confronted with an intrinsic drawback of lacking structural information on the investigated molecules, let alone differentiation of isobaric compounds. In this work, we describe a first attempt to integrate in-source collision-induced dissociation (CID) to the SPI ion source in a SPI-MS instrument. The in-source CID was accomplished by elevating the pressure in the ion source to medium vacuum pressure (MVP) and raising the extraction voltage. With the aid of in-source CID, both the SPI-induced molecular ion and CID-generated fragment ion mass spectra can be obtained to endue each analyte with its unique spectrometric “fingerprint”. The capability for differentiation of isobaric compounds is demonstrated by analyzing two groups of isobaric compounds with molecular weights of 72 and 106 Da, respectively, and quantitative analysis of p-xylene and ethylbenzene in gas mixture. As a result, isobaric compounds with different characteristic fragment ions or appearance energies can be successfully distinguished. The work presents a feasible method for practical applications of SPI-MS to differentiate isobaric compounds conveniently and rapidly without MS/MS technique or coupling additional separation technologies.
A Temperature-Programmed Reaction (TPRn)/Single-Photon Ionization Time-of-Flight Mass Spectrometry (SPI-TOF-MS) system is described. The TPRn/SPI-TOF-MS system allows rapid characterization of heterogeneous catalytic reactions under realistic reaction conditions and at the same time allows for the description of the reaction schemes.
Correction for ‘A temperature-programmed reaction/single-photon ionization time-of-flight mass spectrometry system for rapid investigation of gas–solid heterogeneous catalytic reactions under realistic reaction conditions’ by Songbo He et al., Catal. Sci. Technol., 2015, 5, 4959–4963.
Co-reporter:Wendong Chen, Keyong Hou, Lei Hua and Haiyang Li
Analyst 2015 vol. 140(Issue 17) pp:6025-6030
Publication Date(Web):07 Jul 2015
DOI:10.1039/C5AN00816F
A dopant-assisted reactive low temperature plasma (DARLTP) probe was developed for sensitive and specific detection of explosives by a miniature rectilinear ion trap mass spectrometer. The DARLTP probe was fabricated using a T-shaped quartz tube. The dopant gas was introduced into the plasma stream through a side-tube. Using CH2Cl2 doped wet air as the dopant gas, the detection sensitivities were improved about 4-fold (RDX), 4-fold (PETN), and 3-fold (tetryl) compared with those obtained using the conventional LTP. Furthermore, the formation of [M + 35Cl]− and [M + 37Cl]− for these explosives enhanced the specificity for their identification. Additionally, the quantities of fragment ions of tetryl and adduct ions such as [RDX + NO2]− and [PETN + NO2]− were dramatically reduced, which simplified the mass spectra and avoided the overlap of mass peaks for different explosives. The sensitivity improvement may be attributed to the increased intensity of reactant ion [HNO3 + NO3]−, which was enhanced 4-fold after the introduction of dopant gas. The limits of detection (LODs) for RDX, tetryl, and PETN were down to 3, 6, and 10 pg, respectively. Finally, an explosive mixture was successfully analyzed, demonstrating the potential of the DARLTP probe for qualitative and quantitative analysis of complicated explosives.
Anticoagulant rodenticide diphacinone (DPN) with the common form of sodium diphacinone (SDPN), playing an important role in controlling field rodents and mice in homes, is harmful to both human beings and domestic animals while taken mistakenly or poisoned intentionally. In this work, we propose a simple and rapid method based on thermal desorption ion mobility spectrometry (TD-IMS) for detecting DPN and SDPN. SDPN, with ultra-low vapour pressure, was essentially measured in the form of DPN after its in situ conversion with the assistance of an acid. Under the optimal conditions, the limits of detection (S/N = 3) for SDPN and DPN were less than 0.15 ng μL−1 while their recoveries were 96% and 97%, respectively, and the relative standard deviation for five measurements was less than 6.15%. Finally, the current method was used to detect DPN and SDPN in beverages including green tea, cola, and coffee, demonstrating its capacity in the application for actual samples.
With respect to massive consumption of ammonia and rigorous industrial synthesis conditions, many studies have been devoted to investigating more environmentally benign catalysts for ammonia synthesis under moderate conditions. However, traditional methods for analysis of synthesized ammonia (e.g., off-line ion chromatography (IC) and chemical titration) suffer from poor sensitivity, low time resolution, and sample manipulations. In this work, charge-transfer ionization (CTI) with O2+ as the reagent ion based on a vacuum ultraviolet (VUV) lamp in a time-of-flight mass spectrometer (CTI-TOFMS) has been applied for real-time monitoring of the ammonia synthesis in a microreactor. For the necessity of long-term stable monitoring, a self-adjustment algorithm for stabilizing O2+ ion intensity was developed to automatically compensate the attenuation of the O2+ ion yield in the ion source as a result of the oxidation of the photoelectric electrode and contamination on the MgF2 window of the VUV lamp. A wide linear calibration curve in the concentration range of 0.2–1000 ppmv with a correlation coefficient (R2) of 0.9986 was achieved, and the limit of quantification (LOQ) for NH3 was in ppbv. Microcatalytic synthesis of ammonia with three catalysts prepared by transition-metal/carbon nanotubes was tested, and the rapid changes of NH3 conversion rates with the reaction temperatures were quantitatively measured with a time resolution of 30 s. The high-time-resolution CTI-TOFMS could not only achieve the equilibrium conversion rates of NH3 rapidly but also monitor the activity variations with respect to investigated catalysts during ammonia synthesis reactions.
The application of VUV lamp-based single photon ionization (SPI) was limited due to low photon energy and poor photon flux density. In this work, we designed a quasi-trapping chemical ionization (QT-CI) source with a commercial VUV 10.6 eV krypton lamp for time-of-flight mass spectrometry. The three electrode configuration ion source with RF voltage on the second electrode constitutes a quasi-trapping region, which has two features: accelerating the photoelectrons originated from the photoelectric effect with VUV light to trigger the chemical ionization through ion–molecule reaction and increasing the collisions between reactant ion O2+ and analyte molecules to enhance the efficiency of chemical ionization. Compared to single SPI based on VUV krypton lamp, the QT-CI ion source not only apparently improved the sensitivity (e.g., 12–118 fold enhancement were achieved for 13 molecules, including aromatic hydrocarbon, chlorinated hydrocarbon, hydrogen sulfide, etc.) but also extended the range of ionizable molecules with ionization potential (IP) higher than 10.6 eV, such as propane, dichloroethane, and trichloromethane.
Ion mobility spectrometry (IMS) has become the most deployed technique for on-site detection of trace explosives, and the reactant ions generated in the ionization source are tightly related to the performances of IMS. Combination of multiform reactant ions would provide more information and is in favor of correct identification of explosives. Fast switchable CO3–(H2O)n and O2–(H2O)n reactant ions were realized in a dopant-assisted negative photoionization ion mobility spectrometer (DANP-IMS). The switching could be achieved in less than 2 s by simply changing the gas flow direction. Up to 88% of the total reactant ions were CO3–(H2O)n in the bidirectional mode, and 89% of that were O2–(H2O)n in the unidirectional mode. The characteristics of combination of CO3–(H2O)n and O2–(H2O)n were demonstrated by the detection of explosives, including 2,4,6-trinitrotoluene (TNT), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), ammonium nitrate fuel oil (ANFO), and black powder (BP). For TNT, RDX, and BP, product ions with different reduced mobility values (K0) were observed with CO3–(H2O)n and O2–(H2O)n, respectively, which is a benefit for the accurate identification. For ANFO, the same product ions with K0 of 2.07 cm2 V–1 s–1 were generated, but improved peak-to-peak resolution as well as sensitivity were achieved with CO3–(H2O)n. Moreover, an improved peak-to-peak resolution was also obtained for BP with CO3–(H2O)n, while the better sensitivity was obtained with O2–(H2O)n.
Co-reporter:Chuang Chen, Keyong Hou, Weiguo Wang, Jinghua Li, Haiyang Li
Journal of Chromatography A 2014 Volume 1358() pp:192-198
Publication Date(Web):5 September 2014
DOI:10.1016/j.chroma.2014.06.107
•A nanoESI–IMS working at ambient temperature and pressure was developed.•Complete desolvation and high sensitivity for amines was achieved with the nanoESI–IMS.•The nanoESI–IMS was coupled to HPLC for two dimensional separation and detection of amines without any derivatization.A nanoelectrospray ionization ion mobility spectrometer (nanoESI–IMS) working at ambient pressure and ambient temperature was developed as a detector of high performance liquid chromatography (HPLC) to achieve sensitive detection of amines with no derivatization and meanwhile provide another dimension of separation. The easier desolvation property of the charged droplets formed in nanoESI source enabled complete desolvation of the product ions of sixteen amines and drugs using the nanoESI–IMS at ambient temperature. Working at ambient temperature was good for suppressing the dissociation of thermal volatile ions, such as only the proton adducted molecular ions were observed for morphine in the nanoESI–IMS. Besides, the resolving power of the nanoESI–IMS also showed an increasing tendency as lowering the working temperature, an increment of 19 percent and 10 percent was observed for diethylamine and triethylamine as the temperature dropped from 92 °C to 32 °C. The resolving power of the nanoESI–IMS at 32 °C for the 16 tested compounds was amid 33–44. With the nanoESI–IMS coupled to HPLC, a six-compound mixture including isomers was successfully separated and detected without any derivatization. And linear response ranges of 1 to 20, 0.5 to 20, and 0.8 to 20 μg ml−1 and limits of detection of 0.25, 0.15, and 0.17 μg ml−1 for triethylamine, diethylamine, and butylamine, respectively, were obtained with the hyphenated system. These results showed the excellent performance of the two-dimensional separation and detection method in direct qualitative and quantitative analyses of amines.
Co-reporter:Wendong Chen, Keyong Hou, Lei Hua, Xingchuang Xiong and Haiyang Li
RSC Advances 2014 vol. 4(Issue 28) pp:14791-14794
Publication Date(Web):13 Mar 2014
DOI:10.1039/C4RA00683F
A water-assisted low temperature plasma (WALTP) ionization source based on a quartz T shaped tube was developed for a miniature rectilinear ion trap mass spectrometer to sensitively detect explosives at low picogram levels. By introducing wet air into the plasma stream through the side tube, the explosives responses and repeatability were improved, and the mass spectra were simplified.
Monitoring the exhaled propofol concentration is helpful for anaesthetists to ensure the safety of patients and to adjust the anaesthesia depth. In this study, a trap-and-release membrane inlet ion mobility spectrometer (TRMI-IMS) was constructed for on-line measurement of trace propofol in exhaled air. The effects of trap-and-release parameters such as the trap temperature, release temperature and carrier gas flow rate were investigated. Once optimum experimental parameters were identified, the limits of detection (LODs) for propofol at sampling times of 0.5, 1, 2, and 3 min were found to be 17, 8, 3, and 2 pptv, respectively. With a sampling time of 1 min, the response of TRMI-IMS to propofol was enhanced by a factor of 9 as compared with that of constant temperature MI-IMS; the calibration curve resulting from three individual experiments was linear in the range of 0.1 to 2.5 ppbv. Finally, TRMI-IMS was performed on eleven patients undergoing thyroidectomy surgery to on-line monitor the exhaled propofol. The correlation coefficients (R2) between TRMI-IMS signal intensities and calculated propofol plasma concentrations set in the TCI system were estimated to be in a range of 0.69 to 0.93, demonstrating the potential of TRMI-IMS for on-line predicting the propofol concentration in plasma by exhaled air analysis.
•A sensitive detection method of black powder was developed for IMS by adding chlorinated hydrocarbons in the drift gas.•The current method also showed sub-nanogram sensitivity for common explosives such as ANFO, TNT and PETN.•This method is easy to be adopted in the conventional IMS apparatus for trace explosives detection.This paper introduces a simple method for selective and sensitive detection of black powder by adding chlorinated hydrocarbons in the drift gas instead of changing the structure of conventional ion mobility spectrometer (IMS). The function of chloride modifiers was to substitute Cl−(H2O)n for O2−(H2O)nO2−(H2O)n in the drift region so as to avoid the overlap between O2−(H2O)nO2−(H2O)n and sulfur ion peaks. Among CH2Cl2, CHCl3 and CCl4, CCl4 was chosen as the modifier due to the best peak-to-peak resolution and stability towards the fluctuation of modifier concentration. With 1.4 ppm CCl4 as the modifier, the minimum detectable quantity of 0.1 ng for sulfur was achieved. Moreover, this method showed the ability for detection of common explosives at sub-nanogram level, such as black powder (BP), ammonium nitrate fuel oil (ANFO), 2,4,6-trinitrotoluene (TNT), and pentaerythritol tetranitrate (PETN). In summary, this method requiring no configuration modification has high sensitivity and selectivity, and consumes trace amount of modifier. And these characteristics make it easy to be adopted in current deployed IMS to detect black powder explosives.A simple method was developed for the sensitive detection of black powder using the conventional ion mobility spectrometer by adding 1.4 ppm CCl4 modifier in the drift gas. Moreover, the current method also showed excellent performance for the detection of common military explosives such as ANFO, TNT, and PETN at sub-nanogram level.
Sensitive detection of black powder (BP) by stand-alone ion mobility spectrometry (IMS) is full of challenges. In conventional air-based IMS, overlap between the reactant ion O2–(H2O)n peak and the sulfur ion peak occurs severely; and common doping methods, providing alternative reactant ion Cl–(H2O)n, would hinder the formation of ionic sulfur allotropes. In this work, an ion mobility spectrometer embedded with a titration region (TR-IMS) downstream from the ionization region was developed for selective and sensitive detection of sulfur in BP with CH2Cl2 as the titration reagent. Sulfur ions were produced via reactions between sulfur molecules and O2–(H2O)n ions in the ionization region, and the remaining O2–(H2O)n ions that entered the titration region were converted to Cl–(H2O)n ions, which avoided the peak overlap as well as the negative effect of CH2Cl2 on sulfur ions. The limit of detection for sulfur was measured to be 5 pg. Furthermore, it was demonstrated that this TR-IMS was qualified for detecting less than 5 ng of BP and other nitro-organic explosives.
Ion mobility spectrometry (IMS) is a key trace detection technique for explosives and the development of a simple, stable, and efficient nonradioactive ionization source is highly demanded. A dopant-assisted negative photoionization (DANP) source has been developed for IMS, which uses a commercial VUV krypton lamp to ionize acetone as the source of electrons to produce negative reactant ions in air. With 20 ppm of acetone as the dopant, a stable current of reactant ions of 1.35 nA was achieved. The reactant ions were identified to be CO3–(H2O)n (K0 = 2.44 cm2 V–1 s–1) by atmospheric pressure time-of-flight mass spectrometry, while the reactant ions in 63Ni source were O2–(H2O)n (K0 = 2.30 cm2 V–1 s–1). Finally, its capabilities for detection of common explosives including ammonium nitrate fuel oil (ANFO), 2,4,6-trinitrotoluene (TNT), N-nitrobis(2-hydroxyethyl)amine dinitrate (DINA), and pentaerythritol tetranitrate (PETN) were evaluated, and the limits of detection of 10 pg (ANFO), 80 pg (TNT), and 100 pg (DINA) with a linear range of 2 orders of magnitude were achieved. The time-of-flight mass spectra obtained with use of DANP source clearly indicated that PETN and DINA can be directly ionized by the ion-association reaction of CO3– to form PETN·CO3– and DINA·CO3– adduct ions, which result in good sensitivity for the DANP source. The excellent stability, good sensitivity, and especially the better separation between the reactant and product ion peaks make the DANP a potential nonradioactive ionization source for IMS.
Co-reporter:Wendong Chen, Keyong Hou, Xingchuang Xiong, You Jiang, Wuduo Zhao, Lei Hua, Ping Chen, Yuanyuan Xie, Zhenxin Wang and Haiyang Li
Analyst 2013 vol. 138(Issue 17) pp:5068-5073
Publication Date(Web):14 May 2013
DOI:10.1039/C3AN00555K
A platform consisting of a halogen lamp, a low temperature plasma (LTP) probe, and a miniature rectilinear ion trap mass spectrometer (RIT-MS) has been constructed and evaluated to detect organic and inorganic explosives on solid surfaces. This platform features two attractive characteristics: high sensitivity for the explosives with low volatility, and rapid analysis speed for the explosives on large surface areas. With non-contact heating by the halogen lamp, the signal intensities for the explosives with relatively high volatility were improved by over an order of magnitude, compared to those obtained at room temperature; and even more, the explosives with low volatility, which could hardly be detected at room temperature, were able to be readily identified. The limits of detection (LODs) of the selected explosives were all at the picogram level (e.g., 10 pg and 20 pg for TNT and RDX, respectively) with a heating time of 3 s. Using manual surface swabbing, the analysis of explosives on a large surface area (7.5 cm × 2.5 cm) was accomplished within 10 s, and an acceptable sensitivity could be acquired; additionally, inorganic explosives (black powder and firecracker) were successfully detected. Without any sample pretreatment, the platform was used to analyze the wastewater from an explosives factory, confirming the existence of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,6-dinitrotoluene (2,6-DNT), and the concentration of TNT was determined to be 5 ng mL−1. All these results indicated that the proposed platform was a promising technique for security monitoring and environmental analysis.
Co-reporter:Keyong Hou, Fanglong Li, Wendong Chen, Ping Chen, Yuanyuan Xie, Wuduo Zhao, Lei Hua, Kemei Pei and Haiyang Li
Analyst 2013 vol. 138(Issue 19) pp:5826-5831
Publication Date(Web):10 Jul 2013
DOI:10.1039/C3AN00659J
An in-source, stretched, hollow fiber membrane (HFM) inlet has been developed to improve the sensitivity of on-line time-of-flight mass spectrometry (TOFMS) with a vacuum ultraviolet (VUV) lamp based single photon ionization (SPI) source for the direct analysis of liquid samples. A 2-cm HFM was stretched to 8 cm in length, and placed in the ion source and directly under the VUV lamp window with a distance of 15 mm. Compared with the conventional flow-through configuration under the same experimental conditions, the signal intensities of selected volatile organic compounds (VOCs) of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), benzene, toluene and p-xylene were increased over 5-fold in magnitude, and the response time was shortened to one-third. The limits of detection (LOD) of MTBE, ETBE, benzene, toluene and p-xylene ranged from 0.25 to 1.3 μg L−1 with a measurement time of 60 s, and three orders of linear range were obtained with correlation coefficients of 0.9972–0.9992. The present results suggest that the in-source stretched HFM is a simple and effective way to increase the sensitivity and shorten response time of the membrane inlet, and we believe that it will also be beneficial to other types of on-line mass spectrometer for the on-line analysis of VOCs in water with a VUV lamp based SPI ion source.
In our previous work we proposed a three-zone theory for the Bradbury–Nielsen (BN) gate and proved with a grid–BN structure ion mobility drift tube that enhancements of the three-zone features led to higher resolutions and sometimes higher sensitivities. In this work we continued to seek further improvements of the resolution performance by adopting a BN–grid structure in the same drift tube. The postgate grid works both for confinement of the BN gate induced electric field and for isolation of the injection field from the drift field. This makes it possible to obtain better resolutions by further enhancing the compression electric field and lowering the injection field. It was found in the following experiments that reducing the injection field led to higher resolutions yet lower sensitivities. At an injection field of 140 V/cm, the inverse compression coefficient was found to be much larger than that in the grid–BN structure at all gating voltage differences (GVDs). At GVD = 350 V and a gate pulse width of 0.34 ms, the ion mobility spectrometry efficiency Rm/Rc reached as high as 221% in the BN–grid structure, presenting a further increase compared to 182% in the grid–BN structure. Finally, two examples are given to show the separation power improvements with good resolutions.
A simple space compression-dispersion model for ion transport at ambient pressure was mathematically established. On the basis of this model and aided by SIMION simulation, a three-zone theory was proposed to characterize the Bradbury-Nielsen gating electric field features as three zones: the depletion zone, the dispersion zone, and the compression zone. Then, the influences of gating voltage difference increases on the full width at half-maximum of the Cl– peak were investigated in detail to verify the theory. For example, at a gating voltage difference of 350 V and a gate pulse width of 0.34 ms, the ion packets injected were reduced to as low as 60% of their original widths, with the peak height increased from 756 to 808 pA and the resolution from 18 to 33, enhanced by 7% and ∼80%, respectively. The ion mobility spectrometry (IMS) efficiency ratios, Rm/Rc and Rm/Rp, were also raised above theoretical values and reached about 182% and 175%, respectively. The experimental results were explained using the proposed theory with good consistency. Finally, a compression coefficient was extracted by fitting the experimental data to the applied gate pulse width, presenting a good linearity. All this shows a potential application in improving the performances of ion mobility spectrometry.
Co-reporter:Huapeng Cui, Lei Hua, Keyong Hou, Jing Wu, Ping Chen, Yuanyuan Xie, Weiguo Wang, Jinghua Li and Haiyang Li
Analyst 2012 vol. 137(Issue 2) pp:513-518
Publication Date(Web):01 Dec 2011
DOI:10.1039/C1AN15876G
A home-made stir bar sorptive extraction (SBSE) apparatus was combined to a single photon ionization time-of-flight mass spectrometer (SPI-TOFMS) for rapid and sensitive determination of trace volatile organic compounds (VOCs) in water. The home-made SBSE bar, low-cost and disposable, was used for VOCs extraction. A thermal desorption (TD) device was designed to desorb the analytes from the SBSE bar, and a high throughput interface was developed to transfer the analytes into the ionization chamber of the SPI-TOFMS. The combination of large extraction volume of SBSE bar, and the direct measurement power of SPI-TOFMS enable a short analysis time for VOCs in water with high sensitivity, for example the limits of detection (LODs) were in the range of 7.4–11.1 ng L−1 for benzene, toluene, and p-xylene (BTX) within 15 min. BTX aqueous solutions were chosen to demonstrate the quantitative capability, the linear range was from 0.05 to 100 μg L−1 and the correlation coefficients were better than 0.996. The proposed method was successfully applied for the analysis of VOCs in urban river water.
Co-reporter:Wuduo Zhao, Weiguo Wang, Picheng Qu, Keyong Hou, Haiyang Li
Chemical Physics Letters 2012 Volume 543() pp:55-60
Publication Date(Web):10 August 2012
DOI:10.1016/j.cplett.2012.06.053
To understand the production mechanisms for multiply charged ions Cq+ (q = 2–3) and Iq+ (q = 2–4), the kinetic energy of released electron was measured for understanding the interaction of nanosecond laser with CH3I cluster. The mean electron energy increased from 19 to 33 eV as the laser intensity was raised from 2.9 × 109 to 4.7 × 1010 W/cm2. The evolution of the mean electron energy as a function of laser intensity was similar to that of multiply charged ions, which indicated that electron impact ionization played an important role in the formation of Cq+ (q = 2–3) and Iq+ (q = 2–4). Moreover, the formation of more ionized sites would lead to the cluster splitting, which is disadvantageous for the multiply charged ion production.Graphical abstractHighlights► The production mechanisms for Cq+ and Iq+ (q = 2–4) were studied in CH3I clusters. ► The energetic electrons play an important role for the formation of Cq+and Iq+ (q = 2–4). ► The early splitting of cluster was disadvantageous to the production of multiply charged ions.
Co-reporter:Fenglei Han, Yongzhai Du, Shasha Cheng, Qinghua Zhou, Chuang Chen, KeyongHou, Weiguo Wang, Haiyang Li
International Journal of Mass Spectrometry 2012 Volume 309() pp:13-21
Publication Date(Web):1 January 2012
DOI:10.1016/j.ijms.2011.08.017
A computational fluid dynamics-Monte Carlo approach (abbreviated as CMC) based on SIMION has been developed for simulating the ions trajectories in both the fluid and electric fields simultaneously, the gas flow effect and collision of the ions with the gas molecules are considered within this approach. Four kinds of physical parameters of the instruments can be obtained by this model: the flow field, the electric field, the ion trajectories and the mobility spectrum. A drift tube ion mobility spectrometer was built and simulated to verify this model. The distribution of gas flow field (velocity, pressure, temperature) was simulated by a 2D geometry. The ions trajectories and ion mobility spectra of the IMS were then calculated. The good agreements between simulation and experiment show that the CMC model has predictive power for modeling ion motion at ambient pressure, and this model can serve as visual aids for intuitively understanding the factors that determine ion transport.Graphical abstractHighlights► A simulation model for ion motion at atmospheric pressure was built. ► This model considers both electric field and flow field effects. ► This model combines the computational fluid dynamics and Monte Carlo method. ► Ion trajectories and spectrum in the devices can be seen intuitively with this model.
Co-reporter:Qinghua Zhou, Weiguo Wang, Huaiwen Cang, Yongzhai Du, Fenglei Han, Chuang Chen, Shasha Cheng, Jinghua Li, Haiyang Li
Talanta 2012 Volume 98() pp:241-246
Publication Date(Web):30 August 2012
DOI:10.1016/j.talanta.2012.07.001
The concentration of propofol in patient's exhaled air is an indicator of the anesthetic depth. In the present study, a membrane inlet ion mobility spectrometer (MI-IMS) was built for the on-line measurement of propofol. Compared with the direct sample introduction, the membrane inlet could eliminate the interference of moisture and improve the selectivity of propofol. Effects of membrane temperature and carrier gas flow rate on the sensitivity and response time have been investigated experimentally and theoretically. Under the optimized experimental conditions of membrane temperature 100 °C and carrier gas flow rate 200 mL min−1, the calculated limit of detection (LOD) for propofol was 1 ppbv, and the calibration curve was linear in the range of 10–83 ppbv with a correlation coefficient (R2) of 0.993. Finally, the propofol concentration in an anaesthetized mouse exhaled air was monitored continuously to demonstrate the capability of MI-IMS in the on-line measurement of propofol in real samples.Highlights► A membrane inlet ion mobility spectrometer for measuring propofol was built. ► The membrane inlet eliminated the interference of moisture in the sample gas. ► The membrane inlet improved the selectivity of propofol. ► Experimental conditions affected the sensitivity and response time. ► The propofol concentration in a mouse exhaled air was monitored.
A magnetic field enhanced photoelectron ionization (MEPEI) source combined with single photon ionization (SPI) was developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). A commercial radio frequency (rf) powered vacuum ultraviolet (VUV) lamp was used as SPI light source, and the photoelectrons generated by photoelectric effect were accelerated to induce electron ionization (EI). The MEPEI was obtained by applying a magnetic field of about 800 G with a permanent annular magnet. Compared to a nonmagnetic field photoelectron ionization source, the signal intensities for SO2, SF6, O2, and N2 in MEPEI were improved more than 2 orders with the photoelectron energy around 20 eV, while most of the characteristics of soft ionization still remained. Simulation with SIMION showed that the sensitivity enhancement in MEPEI was ascribed to the increase of the electron moving path and the improvement of the electrons transmission. The limits of detection for SO2 and benzene were 750 and 80 ppbv within a detection time of 4 s, respectively. The advantages of the source, including broad range of ionizable compounds, reduced fragments, and good sensitivity with low energy MEPEI, were demonstrated by monitoring pyrolysis products of polyvinyl chloride (PVC) and the intermediate products in discharging of the SF6 gas inpurity.
A novel combined ion source based on a vacuum ultraviolet (VUV) lamp with both single photon ionization (SPI) and chemical ionization (CI) capabilities has been developed for an orthogonal acceleration time-of-flight mass spectrometer (oaTOFMS). The SPI was accomplished using a commercial 10.6 eV krypton discharge lamp with a photon flux of about 1011 photons s–1, while the CI was achieved through ion–molecule reactions with O2+ reactant ions generated by photoelectron ionization at medium vacuum pressure (MVP). To achieve high ionization efficiency, the ion source pressure was elevated to 0.3 mbar and the photoionization length was extended to 36 mm. As a result, limits of detection (LODs) down to 3, 4, and 6 ppbv were obtained for benzene, toluene, and p-xylene in MVP-SPI mode, and values of 8 and 10 ppbv were obtained for toluene and chloroform, respectively, in SPI-CI mode. As it is feasible to switch between MVP-SPI mode and SPI-CI mode rapidly, this system is capable of monitoring complex organic mixtures with a wide range of ionization energies (IEs). The analytical capacity of this system was demonstrated by measuring dehydrogenation products of long-chain paraffins to olefins through direct capillary sampling and drinking water disinfection byproducts from chlorine through a membrane interface.
A novel bipolar ionization source based on a commercial vacuum-UV Kr lamp has been developed for ion mobility spectrometry (IMS), which can work in both negative and positive ion mode. Its reactant ions formed in negative ion mode were predominantly assigned to be O3−(H2O)n, which is different from that of the 63Ni source with purified air as carrier and drift gases. The formation of O3−(H2O)n was due to the production of ozone caused by ultraviolet radiation, and the ozone concentration was measured to be about 1700 ppmv by iodometric titration method. Inorganic molecules such as SO2, CO2, and H2S can be easily detected in negative ion mode, and a linear dynamic range of 3 orders of magnitude and a limit of detection (S/N = 3) of 150 pptv were obtained for SO2. Its performance as a negative ion source was investigated by the detection of ammonium nitrate fuel oil explosive, N-nitrobis(2-hydroxyethyl)amine dinitrate, cyclo-1,3,5-trimethylene-2,4,6-trinitramine, and pentaerythritol tetranitrate (PETN) at 150 °C. The limit of detection was reached at 45 pg for PETN, which was much lower than the 190 pg using 63Ni ion mobility spectrometry under the same experimental condition. Also, its performance as an ordinary photoionization source was investigated in detecting benzene, toluene, and m-xylene.
Co-reporter:Qinghao Wu, Lei Hua, Keyong Hou, Huapeng Cui, Ping Chen, Weiguo Wang, Jinghua Li, Haiyang Li
International Journal of Mass Spectrometry 2010 Volume 295(1–2) pp:60-64
Publication Date(Web):15 July 2010
DOI:10.1016/j.ijms.2010.06.034
A novel ion source has been introduced in the present study, which combines the characteristics of single photon ionization (SPI) and photoelectron ionization (PEI). The VUV photons for SPI were generated by a commercial krypton discharge lamp (10.6 eV), and the photoelectrons for electron ionization (EI) were produced through photoemission from a stainless-steel skimmer. The energy of photoelectrons can be well controlled by adjusting the voltages applied on the skimmer. The ionization methods, SPI (SPI mode) and SPI combined photoelectron ionization (SPI–PEI mode), can be rapidly switched. Benefited from the higher working pressure in the ion source, the achieved detection limit of benzene and SO2 were 0.1 ppmV and 20 ppmV, respectively. The experimental results show the combined ion source has the potential in chemical process and environmental monitoring.A novel ion source has been introduced in the present study, which combines the characteristics of single photon ionization (SPI) and photoelectron ionization (PEI).
Co-reporter:Nazhen Zhang, Weiguo Wang, Wuduo Zhao, Fenglei Han, Haiyang Li
Chemical Physics 2010 Volume 373(Issue 3) pp:181-185
Publication Date(Web):3 August 2010
DOI:10.1016/j.chemphys.2010.05.002
Abstract
The formation mechanism for multiply charged ions (Cq+ and Oq+ (q = 2–4)) were investigated using a dual polarity time-of-flight mass spectrometer when diethyl ether clusters interacted with nanosecond laser pulse. The signal intensity of multiply charged ions and electron energy was measured experimentally. It was shown that the intensity of multiply charged ions increased about 50 times when laser intensity increased from 7.6 × 109 to 7.0 × 1010 W/cm2, then saturated as laser intensity increased further. It is interesting that the evolution of the mean value of electron energy was same to that of multiply charged ions. The theoretical calculation showed the ionization potential of atomic ions could be significantly decreased due to the effect of Coulomb screening especially at low laser intensity. It indicated that the electron ionization combined with Coulomb screening effect could explain the production of multiply charged ions in nanosecond laser field.
Co-reporter:Nazhen Zhang, Weiguo Wang, Huaiwen Cang, Hailong Wang, Haiyang Li
Chemical Physics Letters 2009 Volume 469(1–3) pp:14-18
Publication Date(Web):3 February 2009
DOI:10.1016/j.cplett.2008.12.012
The electron energies were measured to investigate the influences of laser intensity and wavelength on the ion charge state distribution of Cq+ (q = 2–4) when benzene clusters were irradiated by 109–1011 W/cm2 nanosecond laser pulses. The results show that the ratios of Cq+/C(q−1)+ strongly depend on laser wavelength but slightly on laser intensity. The mean electron energy up to 100 eV was measured, which was qualitatively consisted with the ‘multiphoton ionization ignition-inverse bremsstrahlung heating-electron impact ionization’ three-stage model. The screening effects inside clusters can significantly decrease the ionization potentials of Cq+ and facilitate the formation of multiply charged ions especially at low laser intensity.The ejected electron energy distribution in the interaction of nanosecond-benzene cluster at laser intensity of 1.4 × 1011 W/cm2.
Co-reporter:Xiuming Xu, Huaiwen Cang, Changzhi Li, Zongbao K. Zhao, Haiyang Li
Talanta 2009 Volume 78(Issue 3) pp:711-716
Publication Date(Web):15 May 2009
DOI:10.1016/j.talanta.2008.12.031
A sensor array system consisting of five quartz crystal microbalance (QCM) sensors (four for measuring and one for reference) and an artificial neural network (ANN) method is presented for on-line detection of volatile organic compounds. Three ionic liquids, 1-butyl-3-methylimidazolium chloride (C4mimCl), 1-butyl-3-methylimidazolium hexafluorophosphate (C4mimPF6), 1-dedocyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C4mimNTf2), and silicone oil II, which is widely used as gas chromatographic stationary phase, have been selected as sensitive coatings on the quartz surface allowing the sensor array effective to identify chemical vapors, such as toluene, ethanol, acetone and dichloromethane. The success rate for the qualitative recognition reached 100%. Quantitative analysis has also been investigated, within the concentration range of 0.6–6.1 mg/L for toluene, 0.9–7.5 mg/L for ethanol, 2.8–117 mg/L for dichloromethane, and 0.7–38 mg/L for acetone, with a prediction error lower than 8%.
A new atmospheric pressure air direct current glow discharge (DCGD) ionization source has been developed for ion mobility spectrometry (IMS) to overcome the regularity problems associated with the conventional 63Ni source and the instability of the negative corona discharge. Its general electrical characteristics were experimentally investigated. By equipping it to IMS, a higher sensitivity was obtained compared to that of a 63Ni source and corona discharge, and a linear dynamic range from 20 ppb to 20 ppm was obtained for m-xylene. Primary investigations showed that alkanes, such as pentane, which are nondetectable or insensitively detectable with 63Ni-IMS, can be efficiently detected by DCGD-IMS and the detection limit of 10 ppb can be reached. The preliminary results have shown that the new DCGD ionization source has great potential applications in IMS, such as online monitoring of environment pollutants and halogenated compounds.
Co-reporter:Kemei Pei, Yufang Ma, Xuming Zheng, Haiyang Li
Chemical Physics Letters 2008 Volume 457(4–6) pp:323-328
Publication Date(Web):27 May 2008
DOI:10.1016/j.cplett.2008.04.048
Abstract
Resonance Raman spectra were obtained for p-nitrobenzoic acid using 266, 252.7, and 228.7 nm excitations. The spectra display overtones of the nominal NO2 symmetric stretch mode ν12 and the nominal NO2 antisymmetric stretch ν8, and their combination bands with other four vibrational modes ν19, ν22, ν17 and ν10. A preliminary resonance Raman intensity analysis was done and the results for p-nitrobenzoic acid were compared with nitrobenzene, p-nitroaniline and p-nitrophenone. The results presented here indicate that the Franck–Condon region structure dynamics of nitroaromatic molecules will be dominated by nitro group when both –NO2 and –COOH or –COCH3 chromophores are coexisted in these kinds of molecules.
Co-reporter:Xiuming Xu, Changzhi Li, Kemei Pei, Kun Zhao, Zongbao K. Zhao, Haiyang Li
Sensors and Actuators B: Chemical 2008 Volume 134(Issue 1) pp:258-265
Publication Date(Web):28 August 2008
DOI:10.1016/j.snb.2008.04.039
Six imidazolium-based ionic liquids (ILs) were synthesized and employed as sensing materials coated on quartz crystal microbalance for the detection of organic vapors. Acetone, ethanol, dichloromethane, benzene, toluene and hexane were selected as representatives for common environmental pollutants, and good linear responses from 0 to 100% of concentrations were observed. The halogen-anion-containing imidazolium ILs-coated sensors showed fast response, excellent reversibility, and considerable sensitivity and selectivity towards alcohols, and the selective factors were up to 30 times for ethanol versus other VOCs. The existence of water vapor reduced the frequency response of the sensor, but a good linear relationship remained.
Co-reporter:Kemei Pei, Yufang Ma, Xuming Zheng, Haiyang Li
Chemical Physics Letters 2007 Volume 437(1–3) pp:153-158
Publication Date(Web):22 March 2007
DOI:10.1016/j.cplett.2007.02.013
Resonance Raman spectra of p-nitroacetophenone(PNAP) have been obtained in resonance with the charge-transfer (CT) band using 252.7, 266 and 273.9 nm in methanol solvent. The spectra indicate that the Franck–Condon region photodissociation dynamics have multidimensional character with motion mainly along the CO stretching ν8(1691 cm−1) and the benzene ring stretch ν10(1593 cm−1). A preliminary resonance Raman intensity analysis was done and the results for PNAP were compared with nitrobenzene and aceptophenone. Our results indicate that –NO2 is more photoactive than –COCH3. The isomerization process of PNAP takes place somewhere after the wave packet leaves the Franck–Condon region.Resonance Raman spectra of p-nitroacetophenone (PNAP) have been obtained in resonance with the charge-transfer (CT) band using 252.7, 266 and 273.9 nm in methanol solvent. The spectra indicate that the Franck–Condon region photodissociation dynamics have multidimensional character with motion mainly along the CO stretching ν8(1691 cm−1) and the benzene ring stretch ν10(1593 cm−1). Our results indicate that –NO2 is more photoactive than –COCH3. The isomerization process of PNAP takes place somewhere after the wave packet leaves the Franck–Condon region.
Co-reporter:Yufang Ma, Kemei Pei, Xuming Zheng, Haiyang Li
Chemical Physics Letters 2007 Volume 449(1–3) pp:107-114
Publication Date(Web):26 November 2007
DOI:10.1016/j.cplett.2007.10.044
Abstract
Resonance Raman spectra were acquired for acetophenone using 228.7, 239.5, and 245.9 nm excitations in cyclohexane solution. The spectra display overtones of the benzene ring C–C stretch (1578 cm−1) and the carbonyl CO stretch (1671 cm−1) modes and their combination bands with other five vibrational modes. A preliminary resonance Raman intensity analysis was done and these results for acetophenone were compared to the those previously reported for 2-hydroxyacetophenone. The differences between the vibrational reorganizational energies for acetophenone relative to those of 2-hydroxyacetophenone were briefly discussed.
Chinese Journal of Chemistry 2006 Volume 24(Issue 7) pp:
Publication Date(Web):4 JUL 2006
DOI:10.1002/cjoc.200690162
The structures and stabilities of these still experimentally unknown CHnCl3−nO2-Li+ and CFnCl3−nO2-Li+ ions have been theoretically investigated by ab initio molecular orbital theory and density functional theory (DFT) in conjunction with the 6-311G(d,p), 6-311+G(d,p), 6-311+G(2d,p) and 6-311+G(2df,2p) basis sets. The optimized geometries, chemical bonding and NBO analysis indicate that these complexes of CHnCl3−nO2-Li+ and CFnCl3−nO2- Li+ exist as ion-dipole molecules. The calculated affinity energies of these species exceed 41.9 kJ/mol, which are large enough to suggest the possibility that these title complexes could be detected as stable species in gas phase by Li+ ion attachment mass spectrometry.
Co-reporter:Shuang WANG, Zhe WANG, Ke-Yong HOU, Hai-Yang LI
Chinese Journal of Analytical Chemistry (February 2017) Volume 45(Issue 2) pp:175-182
Publication Date(Web):February 2017
DOI:10.1016/S1872-2040(16)60993-3
A thermal desorption low temperature plasma (TD-LTP) ionization source was developed for the direct, rapid and sensitive detection of pesticides by mass spectrometry without complex sample pretreatment. A thermal desorption sampler was added in front of the plasma generator, and the analyte was collected on a polytetrafluoroethylene (PTFE) swab and desorbed into gas molecules, and then gas molecules were transported to the plasma generator by carrier gas to be ionized. The utilization of thermal desorption sampler helped to transform the interaction between gas phase plasma and sample from gas-solid or gas-liquid to gas-gas, which greatly increased the sensitivity and stability especially for non-volatile sample (e.g. pesticides) compared with conventional LTP ionization source. The TD-LTP ionization source was coupled to a homemade rectilinear ion trap mass spectrometry. The operation parameters of the TD-LTP ionization source were optimized and the characteristic ions of 12 different pesticides were successfully obtained and investigated. Then the TD-LTP ionization source was connected with commercial ACQUITY TQD mass spectrometer, and the pesticide residue level in broomcorn was evaluated.
Monitoring the exhaled propofol concentration is helpful for anaesthetists to ensure the safety of patients and to adjust the anaesthesia depth. In this study, a trap-and-release membrane inlet ion mobility spectrometer (TRMI-IMS) was constructed for on-line measurement of trace propofol in exhaled air. The effects of trap-and-release parameters such as the trap temperature, release temperature and carrier gas flow rate were investigated. Once optimum experimental parameters were identified, the limits of detection (LODs) for propofol at sampling times of 0.5, 1, 2, and 3 min were found to be 17, 8, 3, and 2 pptv, respectively. With a sampling time of 1 min, the response of TRMI-IMS to propofol was enhanced by a factor of 9 as compared with that of constant temperature MI-IMS; the calibration curve resulting from three individual experiments was linear in the range of 0.1 to 2.5 ppbv. Finally, TRMI-IMS was performed on eleven patients undergoing thyroidectomy surgery to on-line monitor the exhaled propofol. The correlation coefficients (R2) between TRMI-IMS signal intensities and calculated propofol plasma concentrations set in the TCI system were estimated to be in a range of 0.69 to 0.93, demonstrating the potential of TRMI-IMS for on-line predicting the propofol concentration in plasma by exhaled air analysis.
Correction for ‘A temperature-programmed reaction/single-photon ionization time-of-flight mass spectrometry system for rapid investigation of gas–solid heterogeneous catalytic reactions under realistic reaction conditions’ by Songbo He et al., Catal. Sci. Technol., 2015, 5, 4959–4963.
A Temperature-Programmed Reaction (TPRn)/Single-Photon Ionization Time-of-Flight Mass Spectrometry (SPI-TOF-MS) system is described. The TPRn/SPI-TOF-MS system allows rapid characterization of heterogeneous catalytic reactions under realistic reaction conditions and at the same time allows for the description of the reaction schemes.
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