Analysis of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products by packed capillary liquid chromatography-electrospray mass spectrometry

Packed capillary column liquid chromatography (LC)-electrospray mass spectrometry (ESI-MS) was used for the first time to detect and identify O-ethyl, S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products, including compounds containing a P-CH3 bond, bis(diisopropylamino)thioalkanes and ureas commonly employed as VX stabilizers. The reported ESI-MS data were generally acquired with a higher sampling cone voltage, a setting that promoted collisionally activated dissociation, and resulted in the acquisition in informative mass spectra containing both molecular and product ion information. The developed method appears to be an attractive alternative to GC-MS for the analysis of aqueous sample containing the degradation products of VX, since they may be analysed directly with little risk of thermal decomposition and without the need for additional sample handling or derivatization. Application of this method to a degraded VX sample resulted in the detection of a number of novel polar and higher-molecular-mass degradation products, not previously associated with VX during GC-MS analysis.     

Fate of the chemical warfare agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX) on soil following accelerant-based fire and liquid decontamination

In the event of alleged use of organophosphorus nerve agents, all kinds of environmental samples can be received for analysis. These might include decontaminated and charred matter collected from the site of a suspected chemical attack. In other scenarios, such matter might be sampled to confirm the site of a chemical weapon test or clandestine laboratory decontaminated and burned to prevent discovery. To provide an analytical capability for these contingencies, we present a preliminary investigation of the effect of accelerant-based fire and liquid decontamination on soil contaminated with the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX). The objectives were (a) to determine if VX or its degradation products were detectable in soil after an accelerant-based fire promoted by aviation fuel, including following decontamination with Decontamination Solution 2 (DS2) or aqueous sodium hypochlorite, (b) to develop analytical methods to support forensic analysis of accelerant-soaked, decontaminated and charred soil and (c) to inform the design of future experiments of this type to improve analytical fidelity. Our results show for the first time that modern analytical techniques can be used to identify residual VX and its degradation products in contaminated soil after an accelerant-based fire and after chemical decontamination and then fire. Comparison of the gas chromatography–mass spectrometry (GC-MS) profiles of VX and its impurities/degradation products from contaminated burnt soil, and burnt soil spiked with VX, indicated that the fire resulted in the production of diethyl methylphosphonate and O,S-diethyl methylphosphonothiolate (by an unknown mechanism). Other products identified were indicative of chemical decontamination, and some of these provided evidence of the decontaminant used, for example, ethyl 2-methoxyethyl methylphosphonate and bis(2-methoxyethyl) methylphosphonate following decontamination with DS2. Sample preparation procedures and analytical methods suitable for investigating accelerant and decontaminant-soaked soil samples are presented. VX and its degradation products and/or impurities were detected under all the conditions studied, demonstrating that accelerant-based fire and liquid-based decontamination and then fire are unlikely to prevent the retrieval of evidence of chemical warfare agent (CWA) testing. This is the first published study of the effects of an accelerant-based fire on a CWA in environmental samples. The results will inform defence and security-based organisations worldwide and support the verification activities of the Organisation for the Prohibition of Chemical Weapons (OPCW), winner of the 2013 Nobel Peace Prize for its extensive efforts to eliminate chemical weapons.     

In situ determination of nerve agents in various matrices by portable capillary electropherograph with contactless conductivity detection

Rapid, efficient and robust methods for sampling and extracting genuine nerve agents sarin, soman and VX were developed for analyzing these compounds on various solid matrices, such as concrete, tile, soil and vegetation. A portable capillary electrophoretic (CE) system with contactless conductometric detection was used for the in situ analysis of the extracted samples. A 7.5 mM MES/HIS-based separation electrolyte accomplished the analysis of target analytes in less than 5 min. The overall duration of the process including instrument start-up, sample extraction and analysis was less than 10 min, which is the fastest screening of nerve agents achieved with liquid phase separation methods to date. The procedure can easily be performed by a person in a protective suit and is therefore suitable for real-life applications. The CE results were validated by an independent GC-MS method and a satisfactory correlation was obtained. The use of a proper sampling strategy with two internal standards and "smart" data-processing software can overcome the low reproducibility of CE. This has a significant impact on the potential acceptance of portable CE instrumentation for the detection and analysis of genuine chemical warfare agents (CWA).     

Application of headspace solid-phase microextraction and gas chromatography-mass spectrometry for detection of the chemical warfare agent bis(2-chloroethyl) sulfide in soil

A field expedient analytical method for detecting the chemical warfare agent (CWA) sulfur mustard as a soil contaminant was developed using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Five commercially available SPME fibers were investigated to determine the optimal fiber, and extraction conditions. Polyacrylate and carbowax-divinylbenzene fiber coatings gave a statistically indistinguishable and best response compared to the other three types examined in a simple system studied without soil. The polyacrylate fiber coating was selected for study of a system in which sulfur mustard was spiked to an agricultural soil (Standard Reference Material 2709, San Joaquin type). With soil samples, the greatest sensitivity occurred by the addition of deionized water to spiked soil and extraction at ambient temperature for 20 min or longer. SPME sampling with GC-MS analyses afforded good reproducibility (relative standard deviation between 2 and 10%), and analyte concentrations as low as 237 ng/g were detected in soil (total ion chromatograms). As completed here, total time for sampling and analysis was just under 1 h, and use of organic solvents or special sample introduction equipment was avoided.     

Photoassisted reaction of chemical warfare agent VX droplets under UV light irradiation

A photoassisted reaction of O-ethyl S-[2-(diisopropylamino) ethyl] methylphosphonothioate (VX) droplets in air was carried out. The experimental results indicated that VX droplets could be easily and chemically transformed into other compounds under irradiation of a germicidal lamp over sufficient time. Quantum chemical calculation results demonstrated that UV light less than 278 nm wavelength could possibly initiate photoreaction of VX and that both P-S and P=O bonds in the VX molecule were lengthened. The identification of reaction products by gas and liquid chromatography mass spectroscopy and NMR revealed that the VX molecule in air under UV light irradiation could undergo isomerization of S-esters to O-esters, cleavage of P-S, S-C, and C-N bonds, and ozonation of tertiary amines.     

Effect of drop size on the degradation of VX in concrete

The effect of drop size on the degradation rate of VX, O-ethyl S-[2-(diisopropylamino)ethyl]methylphosphonothioate, in fresh concrete has been examined using (31)P NMR. Drops of neat VX, ranging in size from 4 microL to 0.2 microL, applied to small concrete coupons (8 mm x 15 mm) were observed to degrade at different rates, with the 1 microL and smaller drops reacting in less than 4 days, and the larger droplets reacting in less than 11 days. Additionally, 4 microL VX predissolved in hexane to evenly spread it over the concrete coupon likewise reacted faster, degrading in less than 5 days. The fresh concrete, less than 2 months old, exhibited significantly faster VX degradation for all drop sizes than that observed for "aged" concrete in a previous study where VX persisted for months. The enhanced reactivity of the "fresh" concrete for VX was maintained for at least a 1-year period. The pH of water containing crushed "fresh" and "aged" concrete was 10.0 and 9.0, respectively. The higher pH of the "fresh" concrete is one reason for its enhanced reactivity toward VX. An additional contribution to the enhanced reactivity of the "fresh" concrete is suggested by the increased mobility of its sorbed VX as evidenced by its significantly narrower peak in (31)P NMR spectra.     

Separation and detection of VX and its methylphosphonic acid degradation products on a microchip using indirect laser-induced fluorescence

The application of indirect LIF (IDLIF) technique for on-chip electrophoretic separation and detection of the nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its major phosphonic degradation products, ethyl methylphosphonic acid (EMPA) and methylphosphonic acid (MPA) was demonstrated. Separation and detection of MPA degradation products of VX and the nerve agent isopropyl methylphosphonofluoridate (GB) are presented. The negatively charged dye eosin was found to be a good fluorescent marker for both the negatively charged phosphonic acids and the positively charged VX, and was chosen as the IDLIF visualization fluorescent dye. Separation and detection of VX, EMPA, and MPA in a simple-cross microchip were completed within less than a minute, and consumed only a 50 pL sample volume. A characteristic system peak that appeared in all IDLIF electropherograms served as an internal standard that increased the reliability of peak identification. The negative peak of both VX and the MPAs is in agreement with indirect detection theory and with previous reports in the literature. The LOD of VX and EMPA by IDLIF was 30 and 37 microM, respectively. Despite the fact that the detection sensitivity is relatively low, the rapid simultaneous on-chip analysis of both VX and its degradation products as well as the separation and detection of the MPA degradation products of both VX and GB, increases detection reliability and may present a choice when sensitivity is not critical compared with speed and simplicity of the assay.     

Characterization of VX on concrete using ion trap secondary ionization mass spectrometry

The nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) was analyzed on the surface of concrete samples using an ion trap secondary ion mass spectrometer (IT-SIMS). It was found that VX could be detected down to an absolute quantity of 5 ng on a concrete chip, or to a surface coverage of 0.0004 monolayers on crushed concrete. To achieve these levels of detection, the m/z 268-->128 ion fragmentation was measured using MS2, where m/z 268 corresponds to [VX + H]+, and 128 corresponds to a diisopropylvinylammonium isomer, that is formed by the elimination of the phosphonothiolate moiety. Detection at these levels was accomplished by analyzing samples that had been recently exposed to VX, i.e., within an hour. When the VX-exposed concrete samples were aged, the SIMS signature for intact VX had disappeared, which signaled the degradation of the compound on the concrete surface. The VX signature was replaced by ions which are interpreted in terms of VX degradation products, which appear to be somewhat long lived on the concrete surface. These compounds include ethylmethylphosphonic acid (EMPA), diisopropyl taurine (DIPT), diisopropylaminoethanethiol (DESH), bis(diisopropylaminoethane) disulfide [(DES)2], and a particularly tenacious compound that may correspond to diisopropylvinylamine (DIVA), or an isomer thereof. It was found that the thiolamine-derived degradation products DIPT, DESH, and (DES)2 were removed with isopropyl alcohol extraction. However, the DIVA-related degradation product was observed to strongly adhere to the concrete surface for longer than one week. Although quantitation was not possible in this set of experiments, the results clearly show the rapid degradation of VX on concrete, as well as the surface sensitivity of the IT-SIMS for intact VX and its adsorptive degradation products.     

Microcolumn liquid chromatography with thermionic detection of the enantiomers of O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX)

An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system. The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).     

用气相色谱-原子发射光谱法检测VX、Bz及其降解产物

应用气相色谱－原子发射光谱（ＧＣ－ＡＥＤ）同时检测Ｓ－（２－二异丙基氨乙基）甲基硫直膦酸乙酯（ＶＸ）、二苯羟乙酸－３－喹咛环酯（ＢＺ）战剂及其降解产物等５种化合物,得取了Ｃ、Ｈ、Ｓ、Ｎ、Ｏ、Ｐ６种元素色谱图,通过选择合适的检测元素,其检出限ＶＸ为１５．６ｍｇ／Ｌ,Ｂｚ为１６．７９ｍｇ／Ｌ,二异基氨基乙太醇为３．０２ｍｇ／Ｌ,３－羟基喹咛为２８．４０ｍｇ／Ｌ,二苯羟乙酸甲酯为３１．７８ｍｇ／Ｌ,定量     

Analysis of VX nerve agent hydrolysis products in wastewater effluents by ion chromatography with amperometric and conductivity detection

An analytical method, based on the use of ion chromatography, was developed to monitor the levels of three regulated VX hydrolysis products in the effluent from a biological wastewater treatment process--ethylmethylphosphonic acid, methylphosphonic acid and 2-(diisopropyl)aminoethanethiol. Previous methods have not been applied to wastewater matrices or 2-(diisopropyl)aminoethanethiol. Despite the specificity and sensitivity constraints of this method, it was possible to measure the compounds in bioreactor effluents down to a level substantially below the US Army discharge limit of 0.1% (w/v). Analytical data was confirmed by liquid chromatography-mass spectrometry (LC-MS) at an independent laboratory.     

Methanol chemical ionization quadrupole ion trap mass spectrometry of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) and its degradation products

Mass spectrometric analysis of O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) degradation products by electron ionization produces extensive fragmentation with little or no molecular ion information making product identification difficult. Milder chemical ionization (CI) is commonly used to provide molecular mass and structure confirmation. In this study, methanol was used as a CI reagent in combination with an ion trap detector for detection and identification of over 30 compounds present in a thermally degraded sample of VX. The use of methanol provides superior results for this class of compounds with less fragmentation than commonly observed with gas reagents and offers logistical advantages for on-site analysis by being easier to transport and safer to use than gas cylinders.     

The Cu- and Zn-complex-catalyzed methanolysis of the chemical warfare nerve agents soman,sarin, and VX

The catalytic methanolysis of the chemical warfare nerve agents soman, sarin, and VX was investigated by using Cu or Zn complexes. Although VX withstood decontamination, the decomposition yield being around 96%, the soman and sarin deposited on different surfaces were almost fully destroyed under ambient conditions. The catalytic tests performed on a wide range of contaminated surfaces confirm the activity of the investigated catalytic systems, these complexes being suitable, from an economical point of view, for use in the formulation of a possible decomposition kit with military or civilian applicability.     

Indirect determination of O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate in air at low concentrations

This paper describes an indirect method for the quantification of the toxic military agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate (VX) in the vapor state in air or other similar gases at ng/m3 levels. The method begins with the passage of a gaseous sample through a filter impregnated with silver fluoride to convert the VX vapor to ethyl methylphosphonofluoridate. The latter compound is then trapped on a bed of Chromosorb 106, transferred to a smaller bed of the same sorbent, and desorbed thermally into a gas chromatograph equipped with a flame-photometric detector. The method is comparable in sensitivity to the principal alternative method, which is based on cholinesterase inhibition, and it is less subject to interference from common organic solvents and other cholinesterase inhibitors. The detection limit was found to be limited by, and therefore dependent on, the nature and extent of any background substances that produced a significant chromatographic signal or response at the retention time of the analyte. In the absence of such substances, the instrument provided a response to 0.19 ng of VX that was thirty times larger than the peak-to-peak noise amplitude on the chromatographic base line. Moreover, the method bias (i.e., 100% minus the percent VX recovery) was found to depend on VX concentration, with estimates of agent recovery ranging from 83% at a VX concentration of 0.67 ng/m3 to 104% at a concentration of 0.084 ng/m3. The relative standard deviation varied with VX concentration and with the nature of the test that was performed to estimate it. It ranged from 2.1% in one VX vapor-challenge test to 17% in an experiment involving spiked sampling tubes, and it was generally lower at the higher VX test concentrations.     

Favorable pendant-amino metal chelation in VX nerve agent model systems

We have performed DFT computational studies [B3LYP, 6-31+G] to obtain metal ion coordination isomers of VX-Me [MeP(O)(OMe)(SCH2CH2NMe2)], a model of two of the most lethal nerve agents: VX [MeP(O)(OEt)(SCH2CH2N(iPr)2)] and Russian-VX [MeP(O)(OCH2CHMe2)(SCH2CH2N(Et)2)]. Our calculations involved geometry optimizations of the neutral VX-Me model as well as complexes with H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+ that yielded 2-8 different stable chelation modes for each ion that involved mainly mono- and bidentate binding. Importantly, our studies revealed that the [O(P),N] bidentate binding mode, long thought to be the active mode in differentiating the hydrolytic path of VX from other nerve agents, was the most stable for all ions studied here. Binding energy depended mainly on ionic size as well as charge, with binding energies ranging from 364 kcal mol(-1) for Be2+ to 33 kcal mol(-1) for K+. Furthermore, calculated NMR shifts for VX-Me correlate to experimental values of VX.     

Catalytic degradation of the nerve agent VX by water-swelled polystyrene-supported ammonium fluorides

The catalytic degradation of the nerve agent VX (O-ethyl S-2-(diisopropylamino)ethyl methylphosphonothioate) by water-swelled polymer-supported ammonium fluorides is described. VX (0.06-0.53 mol/mol F(-)) is rapidly degraded (t(1/2) ～ 10-30 min) to form the "G-analogue" (O-ethyl methylphosphonofluoridate), which hydrolyzes (t(1/2) ～ 1-1.5 h) to the nontoxic EMPA (ethyl methylphosphonic acid). The toxic desethyl-VX is not formed. The catalytic effect of fluoride is maintained even when 6 equiv of VX are loaded. GB (O-isopropyl methylphosphonofluoridate) and desethyl-VX agents are also degraded under these conditions.     

Destruction of chemical warfare agents VX and soman by α‐nucleophiles as oxidizing agents

Reactions of O‐ethyl S‐(2‐diisopropyl‐amino)ethyl methylphosphonothiolate, VX 1 , were investigated with five oxidizing agents. In all the cases, the formation of the VX N‐oxide 7 was observed prior to the subsequent oxidation and hydrolysis into the nontoxic O‐ethyl methylphosphonate 2. Magnesium monoperoxyphthalate (MMPP) is probably one of the most active reagents to achieve the complete detoxification of VX 1 . The decontamination using MMPP was also extended with success to soman 13 , a G‐type agent. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:485–490, 2001     

Degradation kinetics of VX on concrete by secondary ion mass spectrometry

At trace coverages on concrete surfaces, the nerve agent VX (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) degrades by cleavage of the P-S and S-C bonds, as revealed by periodic secondary ion mass spectrometry (SIMS). The observed kinetics were (pseudo-) first-order, with a half-life of 2-3 h at room temperature. The rate increased with surface pH and temperature, with an apparent second-order constant of k(OH) = 0.64 M(-1) min(-1) at 25 degrees C and an activation energy of 50-60 kJ mol(-1). These values are consistent with a degradation mechanism of alkaline hydrolysis within the adventitious water film on the concrete surface. Degradation of bulk VX on concrete would proceed more slowly.     

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX)

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H]⁺) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H]⁺ ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d₁₅ provided evidence that [M+H]⁺ production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H]⁺ ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.     

Decontamination of VX, GD, and HD on a surface using modified vaporized hydrogen peroxide

Vaporized hydrogen peroxide (VHP) has proven efficacy for biological decontamination and is a common gaseous sterilant widely used by industry. Regarding chemical warfare agent decontamination, VHP is also effective against HD and VX, but not GD. Simple addition of ammonia gas to VHP affords reactivity toward GD, while maintaining efficacy for HD (and bioagents) and further enhancing efficacy for VX. Thus, modified VHP is a broad-spectrum CB decontaminant suitable for fumigant-type decontamination scenarios, i.e., building, aircraft, and vehicle interiors and sensitive equipment. Finally, as an interesting aside to the current study, commercial ammonia-containing cleaners are also shown to be effective surface decontaminants for GD, but not for VX or HD.