Performance evaluation of a scent transfer unit for sampling of explosives and their residues to investigate nuisance alerts.

Volatile organic compounds associated with explosives such as Composition C-4 serve as important targets for canine training as well as field analysis. In parallel, 1-bromooctane (1-BO) is a benchmark to contextualize canine performance and aid interpretation of results. Improved understanding of the collection and recovery of these odorants is important for optimizing canine training aids, interpreting canine responses, and better understanding factors that may contribute to nuisance alerts. This study highlights the first known evaluation of the SNT SKR 2000, a scent transfer unit for non-contact sampling of VOCs associated with C-4. The STU unit, along with headspace- solid phase microextraction (HS-SPME) and gas chromatography- mass spectrometry (GC-MS), was evaluated to collect 2,3-dimethyl-2,3-dinitrobutane (DMNB), cyclohexanone, and 2-ethyl-1-hexanol from C-4. Additionally, 1-BO was sampled under identical conditions to provide a simple, non-energetic reference. The sampling parameters comprising of flow rate and sampling time were optimized and it was observed that a low flow rate coupled with a sampling time of 3 min yielded highest recovery of all three VOCS. The STU unit demonstrated reliable detection of VOCs from as little as 664 mg of C-4. 1-BO produced strong, reproducible signals that served as a practical check on sampling consistency. Compound-specific behavior, along with sorption affinity to the sterile gauze pad as well as the SPME fiber, were the key factors responsible for the recovery of the analytes of interest. The STU unit was successful in recovering VOCs from both porous surfaces such as cardboard and non-porous surfaces such as metal paint cans, with higher DMNB retention observed on porous substrates. 1-BO was also recovered from both configurations, illustrating capture from a single-odor environment.