Static secondary ionization mass spectrometry and mass spectrometry/mass spectrometry (MS2) characterization of the chemical warfare agent HD on soilparticle 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 na ture is adsorptive; this attribute makes detection of surface adsorbed HD b y gas-phase approaches difficult, but renders the compound amenable to surf ace detection. Two different ion trap (IT) mass spectrometers, modified to perform secondary ionization mass spectrometry using a ReO4- primary ion be am, 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 cal culations were used to propose structures of the fragment ions. At 0.5 mono layers surface coverage, [HD - Cl](+) and lower mass HD fragment ions were significantly more abundant than the background. At lower concentrations, h owever, the HD secondary ion signal became masked by the background. Sensit ivity and selectivity were significantly improved in the MS2 mode of operat ion. 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/m ass basis. (C) 2001 Elsevier Science B.V.