Aqueous Recovery from Cotton Swabs of Organic Explosives Residue Followed by Solid Phase Extraction

Abstract

Abstract A common procedure for processing cotton swabs containing organic explosives residue involves soaking the cotton in acetone or other organic solvent to extract the explosives, followed by direct analysis of the resulting sample solution using chromatography—mass spectrometry (LC- or GC-MS). A water-based procedure was developed to solve problems arising from co-extraction of sample matrix. Common nitro-organic explosives were extracted from cotton into water; the explosives were isolated by solid phase extraction, using a poly-N-vinylpyrrolidone-divinylbenzene sorbent; samples were screened by LC-UV; and the presence of explosives was confirmed by LC- or GC-MS and fast GC-TEA (EGIS). Explosives residue samples were generated by mixing standards in motor oil on aluminum foil, by detonating four different bombs (C-4, a dynamite, a binary explosive, and TNT) hidden inside suitcases filled with clothing, and by handling a plastic explosive (Semtex H). Ninety-six paired samples were processed by the two procedures (acetone-based and water-based). The water extraction/SPE process was just as effective in recovering organic explosives from cotton swabs, and it better rejected the sample matrix, giving much greater selectivity with all samples except clothing. Water-based samples were screened with high accuracy by LC-UV, and the LC-UV and LC-MS semi-quantitative results were highly correlated.