Direct analysis in real time mass spectrometry (DART-MS) was used to analyze an array of explosives including nitro-based explosives, peroxide explosives, and energetic heterocyclic compounds with different DART discharge gases (helium, argon, and nitrogen). Profound analyte oxidation was observed for particular compounds (TNT (9) and 2, 4-DNT (10)), whose mass spectra were completely dominated by the oxidation products when nitrogen was substituted for helium in DART analysis. This interesting phenomenon suggested that a highly oxidative environment provided by N2 DART ion source. A possible mechanism involved in nitrogen DART was proposed which may help further understanding the different chemistry involved in the ionization process. This work also presents a thermal desorption DART (TD-DART) configuration that can enable rapid, specific analysis of explosives from swipes. The screening of swipes with three different compositions (fiberglass, Hybond N+ membrane, and filter paper) showed that fiberglass swipe has the best performance which was then used for the subsequent TD-DART analysis. A direct comparison of TD-DART with traditional DART demonstrated that TD-DART indeed gives better response than traditional DART (provided that the distance between the DART source and mass spectrometer is the same) and will have wider applications than traditional DART.
Keywords: Explosives; Nitrogen-activated oxidation; Thermal desorption direct analysis in real time mass spectrometry (TD-DART-MS).