Headspace analysis of ammonium nitrate variants and the effects of differing vapor profiles on canine detection

Abstract

Canines continue to be one of the most frequently deployed tool in the detection of explosives, and particularly homemade explosives (HMEs), in part, due to the ease in training to new HME materials as threats arise. The majority of HMEs encountered contain ammonium nitrate (AN), and previous research has measured the release of ammonia from AN, and found that the ammonia vapor concentration varies with form, purity, and environment, but this is has not been correlated to canine detection proficiency. In this research, the headspace analysis of AN variants was carried out using solid phase microextraction (SPME) with gas chromatography/mass spectrometry (GC/MS). Ammonia vapor from the AN was extracted using on-fiber derivatization, while the presence of other volatiles in the headspace of these variants were also characterized by a traditional SPME extraction. These results were correlated to canine testing, where canines previously trained in odor detection were provided laboratory-grade AN for odor imprinting, after which they were to locate other AN variants in a series of simple detection tasks. Headspace analysis showed variations in both the amount of ammonia as well as other volatile compounds in the headspace of the various AN samples, as well as changes in the vapor profiles due to changing environmental conditions. Canine data indicated that the differences in the headspace profiles of the samples may confound detection when canines were trained on laboratory-grade AN alone, while increased ammonia vapor availability from certain samples may have improved detection by this group of canines.