Characterization of Environmental Samples using Ion Trap-Secondary Ion Mass Spectrometry

2-Chloroethyl ethyl sulfide (CEES) is used as a simulant for mustard (HD) in a study to develop secondary ion mass spectrometry (SIMS) for rapid, semi-quantitative detection of mustard on soil. Using SIMS with single-stage mass spectrometry, a signature for CEES can be unequivocally observed only at the highest concentrations (0.1 monolayer and above). Selectivity and sensitivity C2H5SC2Hl from CEES eliminates C,H4 and H2S, which are highly diagnostic. CEES was detected at 0.0012 monolayer on soil. A single analysis could be conducted in under 5 minutes. are markedly improved employing multiple-stage mass spectrometry (MS") using an ion trap. L. cc, cc, W The detection of chemical warfare agent residues on environmental surfaces is an important analytical activity because of the potential for proliferation of these weapons, and for environmental monitoring in areas where they are stored. Historically, one of the most widely used agents has been bis(2-chloroethyl) sulfide, also known as mustard gas and HD. It was initially used in combat in 1917; by the end of the First World War, more than 16% of all casualties were due to chemicals, in most cases mustard.2 Manufacture of mustard is continuing to this day; consequently, there are ongoing opportunities for e~posure .~ Under some conditions, detection of mustard can be challenging. The compound is a semivolatile liquid under ambient conditions, and can strongly adsorb to many surfaces.3d These factors can serve to confound many detection approaches; nevertheless several analytical schemes have been successfully adopted. Among these are a variety of chromatographic method^,^^'^ some of which utilize mass spectrometry as a d e t e ~ t o r . ~ ~ ' ~ All of these techniques rely on getting the compound into the gas phase. An alternative approach is presented in this report, which directly targets strongly sorbed organosulfides. Static secondary ion mass spectrometry (SIMS) can be used to analyze adsorbed contaminants on soil, and has been applied to the detection of organic phosphates6 and amines' in our laboratory. When SIMS is combined with the MWMS capability of an ion trap mass spectrometer, 0