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Characterization of Tear Gas Residues by Ion Mobility Spectrometry

Volume 51, Number 12 (Dec. 1997) Page 1880-1889

Allinson, Graeme; Mcleod, Cameron W.

In this study a hand-held ion mobility spectrometer was used to characterize the vapors produced by alpha-chloroacetophenone (CN) and 2-chlorobenzylidenemalononitrile (CS), their isomers, and their 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 mu g, CS 10 mg; at 50 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 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 dayto-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.