Analysis of dimethylpyrophosphonate decomposition products of VX by GC-MS/MS and P-31 NMR

The detection and identification of decomposition products of chemical warfare agents can be used to investigate allegations of chemical warfare agent use, identify synthetic routes and trace sources of chemical warfare agents and their precursors. Compounds which contain a P-CH3 bond are particularly important as these compounds can provide evidence for the presence or decomposition of organophosphorus nerve agents. Capillary column GC-MS analysis of a distillation fraction of O-ethyl S-[2-diisopropylamino)ethyl]methylphosphonothiolate (VX), a major phosphonothiolate nerve agent, indicated the presence of two additional components comprising about 10% of the total volatile organic content. These compounds were characterized and identified by GC-MS, GC-MS/MS and P-31 NMR as O,O-diethyl dimethylpyrophosphonate and O,O-diethyl dimethylmonothionopyrophosphonate. O,O-Diethyl dimethylmonothionopyrophosphonate presented a structural isomerism ambiguity whereby the position of the sulfur atom could not be defined by MS alone. Identification of the correct structure required spectrometric data from two different techniques, MS/MS and NMR, an important illustration of the use of complementary spectrometric techniques for unambiguous identification of chemicals for verification of the Chemical Weapons Convention.