Forensic analysis of inorganic residues of improvised explosives from post-blast soil samples

Abstract

In recent years, terrorist activities and bombing incidents that are widespread to specific region worldwide have generated the need for rapid investigation on postblast residues. The analysis of inorganic ions contained in homemade explosives and explosive residues in soils demands the rapid determination and identification of explosives compounds and materials used to commit such unlawful bombings. In this study, anions and cations of interest for post-blast identification of homemade explosives were detected and identified using ion chromatography (IC). The postblast explosive residues were extracted from soil samples collected at the seat of simulated explosion point The homemade explosives comprised black powder of various amounts (100 g, 150 g and 200 g). The sample extracts were tested for five anions (Cl\ NC>2‘, NO3', SO42’, SOT) and four cations (Li+, Na+, NRT, KT). Two IC separations were employed, using suppressed IC on a Metrosep Anion Dual 2 column with carbonate eluent for anions, and non-suppressed IC for cations using Metrosep C4 column with nitric acid and dipicolinic acid as eluent. The detection limit for anions ranged from 0.1 - 100 ppb and 0.1 - 84 ppb for cations. All ions showed good linear calibration (rz>0.9326) over the range 1 to 5 ppm. Excellent reproducibility was achieved for within-day and day-to-day variation of target analytes. In black powder standard, three anions (C1' 5 NOi’, SC^2-) and two cations (Na~ and KT) were identified. An additional anion (NO2") was found present in postblast soil samples. The amounts of ions were found to be decreased with decreasing amount of black powder explosive used. By noting the presence of these ions, it was concluded that the explosive contained potassium nitrate which is a strong evidence for the use of black powder explosive in the improvised explosive device.