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 MH ion formation from self-chemical ionization self-CI was examined for four VX degradation products containing the diisopropylamine functional group. A personportable 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, bisdiisopropylaminoethyldisulfide which yielded MH ions only with increased fixed ionization or ion cooling times. Analysis of triethylamined15 provided evidence that MH 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 MH ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.