Anchoring the quantification of VX and Russian VX using portable gas chromatography-mass spectrometry and focusing agents

Field portable gas chromatography-mass spectrometry, GC-MS, have been established as the 'gold standard' of chemical identification and quantification for chemical threats however several chemical warfare agents have been shown to evade required detection limits. This work demonstrates the derivatization of O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate (VX) and N,N-diethyl-2-[methyl(2-methylpropoxy)phosphoryl]sulfanylethanamine (Russian VX, RVX) into VX-G (O-ethyl methylphosphonofluoridate) and RVX-G (O-isobutyl methylphosphonofluoridate) through V-to-G conversion. The G-analogues of VX and RVX are collected on Tenax® TA thermal desorption tubes and are then analyzed by thermal desorption GC-MS. Each thermal desorption tube is loaded with a target-based standard called a focusing agent. Here, we provide relative response factors for the focusing agent diethyl malonate as well as diethyl ethylthiophosphonate that is derivatized into the G-analogue. Our results provide a more reliable and reproducible quantification method for VX (10.4% RSD) and RVX (10.9% RSD) than the bromopentafluorobenzene internal standard (32.9% RSD).