Static secondary ionization mass spectrometry and mass spectrometry/mass spectrometry (MS2) characterization of the chemical warfare agent HD on soil particle surfaces

Detection of the blister agent HD [bis(2-chloroethyl)sulfide] or distilled mustard directly on the surface of soil particles using ion trap secondary ion mass spectrometry in the static mode is demonstrated. HD by its very nature is adsorptive; this attribute makes detection of surface adsorbed HD by gas-phase approaches difficult, but renders the compound amenable to surface detection. Two different ion trap (IT) mass spectrometers, modified to perform secondary ionization mass spectrometry using a ReO4- primary ion beam, were employed in the present study. Sputtered ions were trapped in the gas phase in the IT, where they could be scanned out (MS1), or isolated and fragmented (MS2). The intact HD molecular ion was not observed, however an abundant ion corresponding to [HD - Cl](+) was formed, as were lower mass fragment ions, and ions derived from the chemical background. Ab initio calculations were used to propose structures of the fragment ions. At 0.5 monolayers surface coverage, [HD - Cl](+) and lower mass HD fragment ions were significantly more abundant than the background. At lower concentrations, however, the HD secondary ion signal became masked by the background. Sensitivity and selectivity were significantly improved in the MS2 mode of operation. MS2 of [HD - Cl](+) resulted in production of analytically diagnostic C2H4SH+ and other S- and Cl-bearing fragment ions. HD was detected at 0.07 monolayers using the MS2 approach, which corresponds to 108 ppm on a mass/mass basis. (C) 2001 Elsevier Science B.V.