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Gas Chromatography/Mass Spectrometry (GC/MS) analysis of many chemical agents, particularly the V series, under standard Electron Ionization (EI) conditions often produces extensive fragmentation making identification difficult Milder Chemical Ionization (CI), typically using methane, isobutane, or ammonia as reagent gases, is commonly used to provide molecular weight and structure confirmation. In this study, acetonitrile was used as a liquid CI reagent for detection of HD, VX, and related compounds using an ion trap detector. The protonated molecular ion was observed as the dominant ion and base peak for HD, VX, GA, 1,4-dithiane, 2-diisopropylaminoethanol, and the trimethylsilyl derivatives of methylphosphonic acid and isopropyl methylphosphonic acid. Acetonitrile was not effective for GB. The use of liquid reagents offers logistical advantages for field analysis by being easier to transport and safer to use than gas cylinders. The major drawback of acetonitrile is that it requires significant equilibration time which limits versatility if rapid switching between EI and CI is required.