Measurements of chemical warfare agent degradation products using an electrophoresis microchip with contactless conductivity detector

This paper reports on a microfluidic device for the screening of organophosphonate nerve agent degradation products. The miniaturized system relies on an efficient chip-based separation of alkyl methylphosphonic acids (breakdown products of Sarin, Soman, and VX nerve agents) followed by their sensitive contactless conductivity detection. Experimental parameters relevant to the separation and detection processes have been optimized to yield high sensitivity (with 48-86 microg L(-1) detection limits), fast response (50 s for a three alkyl methylphosphonic acid mixture), high precision (RSD = 3.8-5.0%), and good linearity (over the 0.3-100 mg L(-1) range). Applicability to natural (river) water samples is demonstrated. The new microsystem offers promise for monitoring degradation products of chemical warfare agents, with advantages of speed/warning, efficiency, portability, sample size, and cost compared to conventional ion chromatography or capillary electrophoresis systems.     

Surface-enhanced Raman spectra of VX and its hydrolysis products

Detection of chemical agents as poisons in water supplies not only requires microg/L sensitivity, but also requires the ability to distinguish their hydrolysis products. We have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect chemical agents at these concentrations. Here we expand these studies and present the SERS spectra of the nerve agent VX (ethyl S-2-diisopropylamino ethyl methylphosphonothioate) and its hydrolysis products, ethyl S-2-diisopropylamino methylphosphonothioate, 2(diisopropylamino) ethanethiol, ethyl methylphosphonic acid, and methylphosphonic acid. Vibrational mode assignments for the observed SERS peaks are also provided. Overall, each of these chemicals produces a series of peaks between 450 and 900 cm(-1) that are sufficiently unique to allow identification. SERS measurements were performed in silver-doped sol-gel-filled capillaries that are being developed as part of an extractive point sensor.     

Indirect laser-induced fluorescence detection for capillary electrophoresis using a violet diode laser

The violet (415 nm) diode laser is used for indirect laser-induced fluorescence detection in capillary electrophoretic separations of inorganic anions and chemical warfare agent degradation products. Inorganic anions were detected using 8-hydroxypyrene-1,3,6-trisulfonic acid as the indirect probe and achieved submicromolar (40-80 ppb) detection limits in a 2-min separation. The chemical warfare agent degradation products methylphosphonic acid, ethyl methylphosphonate, isopropyl methylphosphonate, and pinacolyl methylphosphonate were detected using the porphyrin tetrakis(4-sulfophenyl)porphine as the indirect probe and achieved detection limits of 0.1 microM (9 ppb), which are 1 order of magnitude better than that achieved using indirect UV detection. Baseline stability achieved with the violet diode laser was excellent, with dynamic reserve (DR) values of > 1000, which are 15 times better than that achieved using an unstabilized HeCd laser.     

Potentiometric sensing of chemical warfare agents: surface imprinted polymer integrated with an indium tin oxide electrode

Rapid and specific recognition of methylphosphonic acid (MPA), the degradation product of nerve agents sarin, soman, VX, etc., was achieved with potentiometric measurements using a chemical sensor fabricated by a surface imprinting technique coupled with a nanoscale transducer, indium tin oxide (ITO). An octadecylsiloxane thin layer was covalently bound to the ITO-coated glass surface in the presence of MPA. After extraction of MPA, potentiometric measurements showed selective detection of MPA. The selectivity of the sensor has been tested on other alkylphosphonic acids, such as ethylphosphonic acid and propylphosphonic acid, as well as tert-butylphosphonic acid. The viability of the sensor in the presence of other chemical analogues, such as organophosphorus pesticides and herbicides, was investigated.     

V-type nerve agent detection using a carbon nanotube-based amperometric enzyme electrode

An enzyme electrode for the detection of V-type nerve agents, VX (O-ethyl-S-2-diisopropylaminoethyl methylphosphonothioate) and R-VX (O-isobutyl-S-2-diethylaminoethyl methylphosphonothioate), is proposed. The principle of the new biosensor is based on the enzyme-catalyzed hydrolysis of the nerve agents and amperometric detection of the thiol-containing hydrolysis products at carbon nanotube-modified screen-printed electrodes. Demeton-S was used as a nerve agent mimic. 2-(Diethylamino)ethanethiol (DEAET) and 2-(dimethylamino)ethanethiol (DMAET), the thiol-containing hydrolysis product and hydrolysis product mimic of R-VX and VX, respectively, were monitored by exploiting the electrocatalytic activity of carbon nanotubes (CNT). As low as 2 microM DMAET and 0.8 microM DEAET were detected selectively at a low applied potential of 0.5 V vs Ag/AgCl at a CNT-modified mediator-free amperometric electrode. Further, the large surface area and the hydrophobicity of CNT was used to immobilize organophosphorus hydrolase mutant with improved catalytic activity for the hydrolysis of the P-S bond of phosphothiolester neurotoxins including VX and R-VX nerve gases to develop a novel, mediator-free, membrane-free biosensor for V-type nerve agents. The applicability of the biosensor was demonstrated for direct, rapid, and selective detection of V-type nerve agents' mimic demeton-S. The selectivity of the sensor against interferences and application to spiked lake water samples was demonstrated.     

Determination of trace amounts of chemical warfare agent degradation products in decontamination solutions with NMR spectroscopy

Decontamination solutions are used for an efficient detoxification of chemical warfare agents (CWAs). As these solutions can be composed of strong alkaline chemicals with hydrolyzing and oxidizing properties, the analysis of CWA degradation products in trace levels from these solutions imposes a challenge for any analytical technique. Here, we present results of application of nuclear magnetic resonance spectroscopy for analysis of trace amounts of CWA degradation products in several untreated decontamination solutions. Degradation products of the nerve agents sarin, soman, and VX were selectively monitored with substantially reduced interference of background signals by 1D 1H-31P heteronuclear single quantum coherence (HSQC) spectrometry. The detection limit of the chemicals was at the low part-per-million level (2-10 microg/mL) in all studied solutions. In addition, the concentration of the degradation products was obtained with sufficient confidence with external standards.     

Analysis of chemical warfare agents in food products by atmospheric pressure ionization-high field asymmetric waveform ion mobility spectrometry-mass spectrometry

Flow injection high field asymmetric waveform ion mobility spectrometry (FAIMS)-mass spectrometry (MS) methodology was developed for the detection and identification of chemical warfare (CW) agents in spiked food products. The CW agents, soman (GD), sarin (GB), tabun (GA), cyclohexyl sarin (GF), and four hydrolysis products, ethylphosphonic acid (EPA), methylphosphonic acid (MPA), pinacolyl methylphosphonic acid (Pin MPA), and isopropyl methylphosphonic acid (IMPA) were separated and detected by positive ion and negative ion atmospheric pressure ionization-FAIMS-MS. Under optimized conditions, the compensation voltages were 7.2 V for GD, 8.0 V for GA, 7.2 V for GF, 7.6 V for GB, 18.2 V for EPA, 25.9 V for MPA, -1.9 V for PinMPA, and +6.8 V for IMPA. Sample preparation was kept to a minimum, resulting in analysis times of 3 min or less per sample. The developed methodology was evaluated by spiking bottled water, canola oil, cornmeal, and honey samples at low microgram per gram (or microg/mL) levels with the CW agents or CW agent hydrolysis products. The detection limits observed for the CW agents in the spiked food samples ranged from 3 to 15 ng/mL in bottled water, 1-33 ng/mL in canola oil, 1-34 ng/g in cornmeal, and 13-18 ng/g in honey. Detection limits were much higher for the CW agent hydrolysis products, with only MPA being detected in spiked honey samples.     

Zirconia hollow fiber: preparation, characterization, and microextraction application

A zirconia hollow fiber membrane in the macrorange was for the first time successfully synthesized via a template method coupled with a sol-gel process. A polypropylene hollow fiber was employed as the template. The preparation procedure includes repeated impregnation of the template in the proper zirconia sol precursor, and calcination to burn off the template, producing the zirconia hollow fiber. The resulting hollow fiber membrane is almost identical to its template in terms of morphology, exhibiting a hollow core structure. In addition to that, it has a bimodal porous substructure that is different from its template, narrowly distributed nanoskeleton pores, and uniform textural pores or throughpores. The wall thickness and substructures can be conveniently controlled by the synthetic conditions and postheat treatment. Moreover, the thus-prepared zirconia hollow fiber was applied for the microextraction and concentration of a nerve agent degradation product followed by liquid chromatography-mass spectrometric analysis. Since the zirconia fiber exists as an individual device and is directly usable for extracting, handling is more convenient than, for example, an adsorbent in powder form that needs to be coated on a rod for the extraction process. In addition, it is easily prepared and is superior to the monolithic material in this sense. Pinacolyl methylphosphonic acid, one degradation product of organophosphorus nerve agent (soman), was used as the model analyte. Zirconia hollow fiber was demonstrated to be a highly selective adsorbent for the phosphonic acid-containing compounds with high sensitivity. Limit of detection was as low as 0.07 ng/mL (0.39 nM).     

Microchip capillary electrophoresis with electrochemical detection of thiol-containing degradation products of V-type nerve agents

A microchip protocol for the capillary electrophoresis separation and electrochemical detection of thiol-containing degradation products of V-type nerve agents is described. The microchip assay relies on the derivatization reaction of 2-(dimethylamino)ethanethiol (DMAET), 2-(diethylamino)ethanethiol (DEAET), and 2-mercaptoethanol (ME) with o-phthaldialdehyde in the presence of the amino acid valine along with amperometric monitoring of the isoindole derivatives. Both off-chip and on-chip derivatization reactions have led to highly sensitive and rapid detection of the thiol degradation products. Various parameters influencing the derivatization, separation, and detection processes were examined and optimized. These include the amino acid co-reagent, reagent-mixing ratio, reaction time, injection time, separation voltage, and detection potential. The chip microsystem offers a rapid (<4 min) simultaneous detection of micromolar concentrations of DMAET, DEAET, and ME. Linear calibration plots were observed for the V-type nerve agent thiol degradation products, along with good stability and reproducibility (RSD < 8.0%). Detection limits of 5 and 8 microM were obtained for the off-chip reaction of DMAET and DEAET, respectively, following a 2-s injection. The suitability for assays of environmental matrixes was demonstrated for the determination of DMAET and DEAET in untreated tap and river water samples. The favorable analytical performance makes the new microfluidic device attractive for addressing the needs of various security scenarios.     

Extraction of nerve agent VX from soils

The development and optimization of a method allowing the extraction of intact organophosphorus chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) from several types of soils are presented here. This involved the selection of an appropriate buffer to bring the sample to a pH close to the pK(a) of VX but sufficiently low to avoid its basic hydrolysis. Buffering with Tris (pH 9) and subsequent extraction of the aqueous layer by a 85:15 (v/v) hexane/dichloromethane mixture allows rapid and sensitive flame photometric detection of VX at spiking levels lower than 10 microg x g(-1), even after 3 months of aging. Extraction yields were close to 60% in complex matrixes. This method also allows recovery and identification of a characteristic degradation product of VX, bis(2-diisopropylaminoethyl) disulfide, which appears to be formed during the aging process. The performance of this method is far better than that of OPCW reference operating procedure, which does not allow extraction of detectable amounts of VX (spiked at 10 microg x g(-1)) in one of the soils used for this study.     

Application of a microcoil probe head in NMR analysis of chemicals related to the chemical weapons convention

A 1.7-mm microcoil probe head was tested in the analysis of organophosphorus compounds related to the Chemical Weapons Convention. The microcoil probe head demonstrated a high mass sensitivity in the detection of traces of organophosphorus compounds in samples. Methylphosphonic acid, the common secondary degradation product of sarin, soman, and VX, was detected at level 50 ng (0.52 nmol) from a 30-microL water sample using proton-observed experiments. Direct phosphorus observation of methylphosphonic acid with (31)P{(1)H} NMR experiment was feasible at the 400-ng (4.17 nmol) level. Application of the microcoil probe head in the spiked sample analysis was studied with a test water sample containing 2-10 microg/mL of three organophosphorus compounds. High-quality (1)H NMR, (31)P{(1)H} NMR, 2D (1)H-(31)P fast-HMQC, and 2D TOCSY spectra were obtained in 3 h from the concentrated 1.7-mm NMR sample prepared from 1 mL of the water solution. Furthermore, a 2D (1)H-(13)C fast-HMQC spectrum with sufficient quality was possible to measure in 5 h. The microcoil probe head demonstrated a considerable sensitivity improvement and reduction of measurement times for the NMR spectroscopy in identification of chemicals related to the Chemical Weapons Convention.     

Determination of chemical warfare agent degradation products at low-part-per-billion levels in aqueous samples and sub-part-per-million levels in soils using capillary electrophoresis

A significant enhancement in the method detection limits is observed in the analysis of chemical warfare agent (CWA) degradation products in environmental samples by capillary electrophoresis (CE) using electrokinetic injection. The CE method uses indirect UV detection of the nonderivitized acidic analyte and a cationic surfactant, didodecyldimethylammonium hydroxide, for reversal of the electroosmotic flow. Analytes studied include the dibasic acid methylphosphonic acid (MPA) and its monoacid/monoalkyl esters, RMPA, where R = ethyl, isopropyl, and pinacolyl (2-(3,3-dimethylbutyl)). The CE method uses an attractive buffer system which is highly stable and inexpensive, and, in addition to reversing the electroosmotic flow, provides excellent separation efficiencies within a 3-min run. This CE method is also free from interference caused by carbonate, humic acids, and fluoride. Compared to pressure injection, electrokinetic injection with this CE buffer system provided substantially lower detection limits, up to 100-fold lower for samples in reagent water. However, to best realize the benefits of the electrokinetic injection enhancement for environmental samples, a prior cleanup of the sample using standard ion-exchange cartridges is necessary. This cleanup step uses sequential cartridges to remove sulfate (barium cartridge), chloride (silver cartridge), and cations (H+ cartridge). Using this approach, detection limits for these four acids were as low as 1-2 micrograms/L for water samples and 25-50 micrograms/L for aqueous leachates of soil samples (10 mL of leachate/1.5 g of soil). The utility of this method for separation of CWA degradation products by CE is discussed in terms of pressure injection versus electokinetic injection. The effects of voltage and time of injection on the separation were investigated. Results from three types of soils and four types of water (groundwater, artificial seawater, tap water, bay water) indicated that the method has potential for environmental monitoring. Quantitative CE analysis with electrokinetic injection enhancement of detection limits of these types of environmental samples requires the use of an appropriate internal standard approach. The data presented here indicate that an internal standard-based approach could be expected to give analysis results in the sub-part-per-million concentration range of 90-110% of the true value.     

模拟太阳光下锗掺杂纳米TiO2对化学毒剂的降解性能

采用均匀沉淀法制备不同锗掺杂浓度的纳米二氧化钛(TiO₂); 为了研究掺杂浓度与粉体活性之间的关系, 针对化学毒剂(CWAs)模拟剂2-氯乙基乙基硫醚(2-CEES)和甲基膦酸二甲酯(DMMP)开展光催化消毒实验, 并用动力学方程拟合实验结果; 通过XRD、UV-Vis、BET、BJH、SEM和TEM等技术对样品进行表征, 分析锗掺杂对TiO₂结构及性能的影响; 综合考虑溶剂的毒性、挥发性、可燃性和溶解性等因素, 以氢氟醚(HFE)作为分散溶剂, 研究模拟太阳光下Ge-TiO₂和HFE混合体系对芥子气(HD)、梭曼(GD)和维埃克斯(VX)的消毒性能。结果表明: 适量锗掺杂不会改变纳米TiO₂的晶型结构, 可以减小晶粒尺寸, 增大比表面积, 增强光利用率, 提高消毒活性; 相较于直接使用粉体消毒, 混合体系的消毒效率明显提高; 在模拟太阳光下, 最佳锗掺杂浓度(6.24wt%)样品与HFE-458 (HCF₂CF₂CH₂OCF₂CF₂H)组成的混合体系与三种化学毒剂反应60 min的降解率分别为: HD 98.73%、GD 100%、VX 100%。     

Adsorption of dimethyl methylphosphonate on metal impregnated carbons under static conditions

Active carbon, grade 80 CTC, of surface area 1199m(2)/g, 12x30 BSS particle size and coconut shell origin was impregnated (5%, W/W) with various impregnants such as Cu(II) 1,1,1,5,5,5-hexafluoroacetylacetonate, Cu(II) 1,1,1-trifluoroacetylacetonate, 1-phenylbute-1,3-dione-2-oxime plus Cu(II) using incipient wetness technique. These impregnated carbons along with active carbon (Grade 80 CTC) and whetlerite were studied for the adsorption of dimethyl methylphosphonate (DMMP) at 33+/-1 degrees C under static conditions. Cu(II) 1,1,1,5,5,5-hexafluoroacetylacetonate impregnated carbon system showed highest uptake (68.5%, W/W) of DMMP amongst all the carbon systems, however, active carbon with higher surface area could adsorb 61.5% (W/W) of DMMP under same conditions. It indicated that the adsorption by Cu(II) 1,1,1,5,5,5-hexafluoroacetylacetonate impregnated carbon was not only due to physisorption but chemisorption as well. Kinetics of adsorption was also studied and various parameters such as equilibration time, equilibration capacity, rate constant (k), diffusional exponent (n) and constant (K) were determined. Carbons with and without DMMP exposure were also studied using IR and TGA techniques. Reaction products were analyzed using gas chromatography coupled with mass spectrometry (GC/MS) and found to be methyl methylphosphonic acid (MMPA) and methylphosphonic acid (MPA) for Cu(II) 1,1,1,5,5,5-hexafluoroacetylacetonate impregnated carbon.     

Rapid screening of aqueous chemical warfare agent degradation products: ambient pressure ion mobility mass spectrometry

The use of electrospray ionization ambient pressure ion mobility spectrometry with an orthogonal reflector time-of-flight mass spectrometer to analyze chemical warfare (CW) degradation products from aqueous environmental samples has been demonstrated. Certified reference materials of analytical standards for the detection of Schedule 1, 2, or 3 toxic chemicals or their precursors as defined by the chemical warfare convention treaty verification were used in this study. A combination of six G/V-type nerve and four S-type vesicant related CW agent degradation products were separated with baseline resolution by this instrumental technique. Analytical figures of merit for each CW degradation product were determined. In some cases, reduced mobility constants (K0) have been reported for the first time. linear response ranges for the selected CW degradation products were found to be generally approximately 2 orders of magnitude, where the overall dynamic response ranges were found to extend to 4 orders of magnitude. Limits of detection for five of the nine chemical products tested were found to be less than 1 ppm. To demonstrate the potential of this instrumental method with complex mixtures, four CW degradation products were separated and detected from a spiked Palouse River water sample in less than 1 min. Finally, a homologous series of n-alkylamines were used as baseline reference standards, producing a mobility/mass trend line to which the CW degradation products could be compared. Comparison of these products in this manner is expected to reduce the number of false positive/negative responses.     

Kinetics and mechanism of degradation of p-chloronitrobenzene in water by ozonation

The kinetics and mechanism of p-chloronitrobenzene (pCNB) degradation by ozone were investigated. With reference compounds, nitrobenzene (NB) and chlorobenzene (CB), reaction rate constants of pCNB with O3 and OH were measured by means of competition kinetics (mixtures of pCNB and NB, or pCNB and CB), with the rate constants being, 1.6 L mol(-1) s(-1), 2.6 x 10(9) L mol(-1) s(-1), respectively. During the ozonation process of pCNB, an increase of chloride and nitrate ions in the water sample solution was observed, which is consistent with the decrease in pCNB concentration. But the total organic carbon (TOC) removal rate is not consistent with the pCNB elimination rate indicating only part of pCNB was mineralized and thus presumably some intermediate products were formed. The pCNB degradation intermediate products were analyzed by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), high performance liquid chromatography (HPLC) and ion chromatography (IC). The main intermediate products were phenol, p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol, 5-chloro-2-nitrophenol, 5-nitro-catechol, para-benzoquinone, 5-nitro-1,2,3-trihydroxy phenol, trihydroxy semiquinone, glycolic acid, oxalic acid, hydroxybutanoic acid, mesoxalic acid, tartrouic acid, malonic acid, maleic acid, hydroxymalonic acid, tartaric acid, malic acid, ketoglutaric acid and muconic acid. From the identified reaction products, a possible degradation pathway for the ozonation of pCNB has been proposed.     

Improved tert-butyldimethylsilylation gas chromatographic/mass spectrometric detection of nerve gas hydrolysis products from soils by pretreatment of aqueous alkaline extraction and strong anion-exchange solid-phase extraction

In the analysis of tert-butyldimethylsilyl derivatives (IBDMS) of alkyl methylphosphonic acids (RMPA) and methylphosphonic acid (MPA), from soils by gas chromatography/mass spectrometry (GC/MS), the detection yields are generally low, due to the suppression of TBDMS derivatization by the soil matrix components and the adsorption of RMPA and MPA to the soils. An ion-exchange pretreatment of the aqueous soil extract can be used to overcome the former factor by removing interfering compounds. A pretreatment method is described for improving the detection yields due to the latter factor, using an alkaline extraction procedure. The recovery was estimated quantitatively using capillary electrophoresis. The soil samples tested included volcanogenous immature soils and showed a low aqueous extraction recovery and GC/MS detection yields. The inclusion of sodium hydroxide in the extraction solvent dramatically increased the recovery. Using a 0.1 M sodium hydroxide solution, the recovery was in excess of 68%. Interfering components were removed from the alkaline soil extract by solid-phase extraction of the acids on a silica-based strong anion exchanger. The alkaline soil extract was neutralized with hydrofluoric acid and applied to the cartridge in the fluoride form. After washing with water, MPA and RMPA could be eluted with methanolic ammonia nearly quantitatively. Using the established pretreatment method, MPA and RMPA were detected from all the soil samples in more than 67% yield.     

Time-Efficient LC/MS/MS Determination of Low Concentrations of Methylphosphonic Acid

A time-efficient protocol for quantification of methylphosphonic acid (MPA), a final hydrolysis product of nerve agents in aqueous environments, via liquid chromatography mass spectrometry is described. Chromatographic separation and mass spectrometry detection conditions are optimized to enable high sensitivity, selectivity, and accuracy of the approach and to eliminate impeding matrix effects associated with the analysis of water samples of natural origin. The developed technique is tested by analyzing the samples of natural waters that are spiked with a known quantity of MPA. With direct LC/MS/MS, the detection limit for MPA in natural waters is 10 ng/mL.     

Quantification of VX vapor in ambient air by liquid chromatography isotope dilution tandem mass spectrometric analysis of glass bead filled sampling tubes

An analysis method has been developed for determining low parts-per-quadrillion by volume (ppqv) concentrations of nerve agent VX vapor actively sampled from ambient air. The method utilizes glass bead filled depot area air monitoring system (DAAMS) sampling tubes with isopropyl alcohol extraction and isotope dilution using liquid chromatography coupled with a triple-quadrupole mass spectrometer (LC/MS/MS) with positive ion electrospray ionization for quantitation. The dynamic range was from one-tenth of the worker population limit (WPL) to the short-term exposure limit (STEL) for a 24 L air sample taken over a 1 h period. The precision and accuracy of the method were evaluated using liquid-spiked tubes, and the collection characteristics of the DAAMS tubes were assessed by collecting trace level vapor generated in a 1000 L continuous flow chamber. The method described here has significant improvements over currently employed thermal desorption techniques that utilize a silver fluoride pad during sampling to convert VX to a higher volatility G-analogue for gas chromatographic analysis. The benefits of this method are the ability to directly analyze VX with improved selectivity and sensitivity, the injection of a fraction of the extract, quantitation using an isotopically labeled internal standard, and a short instrument cycle time.     

Analysis of VX on soil particles using ion trap secondary ion mass spectrometry.

The direct detection of the nerve agent VX (methylphosphonothioic acid, S-[2-[bis(1-methylethyl)amino]ethyl] O-ethyl ester) on milligram quantities of soil particles has been achieved using ion trap secondary ion mass spectrometry (IT-SIMS). VX is highly adsorptive toward a wide variety of surfaces; this attribute makes detection using gas-phase approaches difficult but renders the compound very amenable to surface detection. An ion trap mass spectrometer, modified to perform SIMS, was employed in the present study. A primary ion beam (ReO4-) was fired on axis through the ion trap, where it impacted the soil particle samples. [VX + H]+, [VX + H]+ fragment ions, and ions from the chemical background were sputtered into the gas-phase environment of the ion trap, where they were either scanned out or isolated and fragmented (MS2). At a surface concentration of 0.4 monolayer, intact [VX + H]+, and its fragment ions, were readily observable above background. However, at lower concentrations, the secondary ion signal from VX became obscured by ions derived from the chemical background on the surface of the soil particles. MS2 analysis using the ion trap was employed to improve detection of lower concentrations of VX: detection of the 34S isotopic ion of [VX + H]+, present at a surface concentration of approximately 0.002 monolayer, was accomplished. The study afforded the opportunity to investigate the fragmentation chemistry of VX. Semiempirical calculations suggest strongly that the molecule is protonated at the N atom. Deuterium labeling showed that formation of the base peak ion (C2H4)N(i-C3H7)2+ involves transfer of the amino proton to the phosphonothioate moiety prior to, or concurrent with, C-S bond cleavage. To manage the risk associated with working with the compound, the vacuum unit of the IT-SIMS was located in a hood, connected by cables to the externally located electronics and computer.