False Positive Signals in the Detection of Explosives by Ion Mobility Spectrometry: Organic Acids

We studied 20 varieties of fruits (fruits, berries, and vegetables), the presence of trace amounts of which in samples caused false positive signals in an explosives detector based on ion mobility spectrometry. These signals were due to the presence of organic acids, which effectively form negative ions, in the fruits. The mobilities of some types of ions of these acids were close to or coincided with the mobilities of ions of explosives. In particular, the ions of ascorbic or citric acid, malic acid, tartaric acid, the adduct anions of oxalic and malic acids, and the adduct anions of citric and malic acids were identified by the detector as the ions of 2,4-dinitrotoluene, 1,2,3-trinitroxypropane, HMX, and 2,4,6-trinitrotoluene and the adduct anions of hexogen and lactic acid, respectively.