Combined Solid‐Phase Extraction of Organic, Organic Peroxide, and Inorganic Explosives for Post‐Blast Residue Analysis

ABSTRACT Post‐blast explosives residue may contain organic and/or inorganic explosives. Current methods employed involve splitting the sample swab in two for syringe extraction for each explosive type (acetone for organics, water for inorganics). A comprehensive solid‐phase extraction (SPE) trace sample clean‐up procedure for the combined recovery of 12 organic, 2 organic peroxide, and 15 inorganic analytes from explosives residue on cotton swabs is demonstrated and validated. By keeping the sample whole and using a single extraction process, the proposed method saves time, provides a more representative sample, and increases the possibility of detecting explosives that might be present on collection swabs. Thus, recoveries are improved for one class of explosives without sacrificing recoveries of another analyte or explosives class in the process. Extractions were demonstrated by syringe filtration and SPE from cotton balls (CBs) and cotton‐tipped applicators (CAs). For SPE of both matrices, organic explosives (nitramines, nitrate esters, nitroalkanes, and nitroaromatics) had a limit of detection (LOD) of 500 ppb or lower, organic peroxides had higher LODs at 5 ppm or lower, and most inorganic anions and cations had LODs at 1 ppm or lower. Application to 32 post‐blast samples, 9 burned powders simulating post‐blast, and 1 pre‐blast sample successfully demonstrated the SPE method with both cotton matrices in a comparison study of the two extraction procedures. SPE resulted in a lower false screen rate (number of compounds that met the screening criteria, but not confirmed present) when compared to syringe extraction.