Characterization of Tear Gas Residues by Ion Mobility Spectrometry

Abstract

In this study a hand-held ion mobility spectrometer was used to characterize the vapors produced by α-chloroacetophenone (CN) and 2-chlorobenzylidenemalononitrile (CS), their isomers, and then-degradation products at ambient temperature and 50 °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 μg, CS 10 mg; at 50 °C, CN 0.5 μg, CS 16 μg; and in the positive-ion acquisition mode at ambient temperature, CN 0.5 μg, CS not detected; at 50 °C, CN 0.1 μg, 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.