Characterization of tear gas residues by ion mobility spectrometry

In this study a hand-held ion mobility spectrometer was used to characterize the vapors produced by cu-chloroacetophenone (CN) and 2-chlorobenzylidenemalononitrile (CS), their isomers, and their degradation products at ambient temperature and 50 degrees C, and in both the positive-and negative-ion acquisition modes, Minimum determinable residues were as follows: in the negative-ion acquisition mode at ambient temperature, CN 0.5 mu g, CS 10 mg; at 50 degrees C, CN 0.5 mu g, CS 16 mu g; and in the positive-ion acquisition mode at ambient temperature, CN 0.5 mu g, CS not detected; at 50 degrees C, CN 0.1 mu g, CS not detected, The steady-state reproducibility was found to be independent of ion acquisition mode but dependent on signal intensity and background noise [relative standard deviation (RSD) 3-17%]--the smaller the signal, the greater the variation, The day-to-day variation in positive-and negative-mode signal intensities showed the same trends (RSD 3-33%), By comparing positive-and negative-ion mode spectra, it was possible to differentiate not only between CN and CS but also between their isomers and breakdown products.