Huanwen Chen

Neutral Desorption Using a Sealed Enclosure to Sample Explosives on Human Skin for Rapid Detection by EESI-MS

A novel air-tight neutral desorption enclosure has been fabricated to noninvasively sample low picograms of explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), triacetone triperoxide (TATP), and nitroglycerin (NG) from human skin using a neutral nitrogen gas beam. Without further sample pretreatment, the explosive mixtures collected from the skin surface were directly transported by a nitrogen carrier gas over a 4-m distance for sensitive detection and rapid identification by extractive electrospray ionization tandem mass spectrometry.

Development of extractive electrospray ionization ion trap mass spectrometry for in vivo breath analysis

In metabolomics studies and clinical diagnosis, interest is increasing in the rapid analysis of exhaled breath. In vivo breath analysis offers a unique, unobtrusive, non-invasive method of investigating human metabolism. To analyze breath in vivo, we constructed a novel platform of extractive electrospray ionization (EESI) ion trap mass spectrometry (ITMS) using a home-made EESI source coupled to a linear trap quadrupole mass spectrometer. A reference compound (authentic n-octyl amine) was used to evaluate effects of systematically varying selected characteristics of the EESI source on signal intensity. Under the optimized working conditions, metabolic changes of human bodies were in vivo followed by performing rapid breath analysis using the multi-stage EESI-ITMS tandem mass spectrometry platform. For nicotine, a limit of determination was found to be 0.05 fg mL(-1) (S/N = 3, RSD = 5.0 %, n = 10) for nicotine in aerosol standard samples; the dynamic response range was from 0.0155 pg mL(-1) to 155 pg mL(-1). The concentration of nicotine in the exhaled breath of a regular smoker was in vivo determined to be 5.8 pg mL(-1), without any sample pre-treatment. Our results show that EESI-ITMS is a powerful analytical platform to provide high sensitivity, high specificity and high throughput for semi-quantitative analysis of complex samples in life science, particularly for in vivo metabolomics studies.

Imaging Melamine in Egg Samples by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

The characteristic fragment (m/z 85) of protonated melamine, generated in MS/MS spectra recorded from the surface of egg slices using surface desorption atmospheric pressure chemical ionization mass spectrometry (SDAPCI-MS), has been used to image melamine in slices of cooked egg. The experimental results showed that the spatial resolution of the imaging using SDAPCI-MS was 0.06 mm2. Egg yolk was proven to have little melamine in this study, and the most melamine was contained in egg white region, although not evenly distributed.

Instrumentation and Characterization of Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract By combining the advantages of desorption electrospray ionization (DESI) and atmospheric pressure chemical ionization (APCI), a novel ambient surface desorption atmospheric pressure chemical ionization (SDAPCI) source is developed for direct detection of trace amounts of analytes in various complex matrices without any sample pre-treatment. In the SDAPCI source, a self-assembled corona discharge was employed to generate the primary ions, which were directed to impact the sample surface to yield positive/negative ions of analytes for mass analysis. Using ambient air (about 45%–60% relative water moisture) as a reactive reagent for chemical ionization to generate primary ions such as H3O+ in positive ion detection mode or H2O·OH− in negative ion detection mode, SDAPCI allows mass spectrometric analysis of ambient samples without toxic contamination, and provides simplicity in its implementation for in-situ analysis in a miniature mass spectrometer. The principle and construction of an SDAPCI source are presented in this contribution. Successful detection of trace amounts of active ingredients of various pharmaceutical preparations was demonstrated using the homemade SDAPCI source with ambient air as the reactive reagent. Using pure argon gas instead of the ambient air, radical cations of acetaminophenol and peptide I–7 were successfully observed and structurally characterized by MS/MS experiments, which provided the experimental evidences for the production of radical cations of peptides at atmospheric pressure. The data show promising applications of SDAPCI-MS for direct analysis of ambient surfaces with neither sample pre-treatment nor toxic chemical contamination.

Rapid Detection of Toluene-2,4-diisocyanate in Various Sports Fields Using Extractive Electrospray Ionization Mass Spectrometry

Abstract Plastic materials that release free toluene-2,4-diisocyanate (TDI) can be commonly found in sports venues. As the presence of TDI in the atmosphere will result in severe air pollution, the WHO has enforced strict regulations to ensure that the proportion of the free TDI monomer in the isocyanate-polymer is lower than 0.5%. In this study, ambient air samples containing trace amounts of TDI-water aerosols were collected with glass syringes on the spot and then directly injected into a home-made extractive electrospray ionization (EESI) source. The EESI source was installed on a LTQ-MS instrument for the direct analysis of samples with complex matrices. The raw samples were directly analyzed by tandem EESI-MS without any sample pretreatment under the following working conditions: spray voltage, 3 kV; capillary voltage, 21 V; and capillary temperature, 175 °C. A single sample analysis, along with tandem MS experiments for enhanced specificity, was completed within 1 s. The limit of detection was found to be less than 0.04% ( n = 5, S/N = 100), considerably lower than that allowed in the air. The relative standard deviation of the analysis results was no higher than 1.4%.