Desenvolvimento de métodos por cromatografia iônica para análise de explosivos e produtos de explosão

Abstract

The criminal use of explosives, especially in attacks on ATMs, is still frequent in Brazil. The most used explosives are mixtures of fuels and inorganic oxidizers, such as ammonium nitrate and black powder. The main technique for the analysis of inorganic explosives is ion chromatography, but the sampling step is crucial in providing representative and reliable results. Therefore, in this work ion chromatography methods with suppression and conductimetric detection were developed for the analysis of 8 cations and 18 anions, and different materials and collection procedures were also evaluated. The chromatographic methods were validated and the analytes that passed all the statistical tests were barium, calcium, strontium, magnesium, nitrate and potassium, presenting precision, recovery and limits of detection and quantification compatible with works by other authors. Three brands of swabs were evaluated as possible sampling materials, initially showing significant amounts of various ions, which were mostly removed by a washing procedure with ultrapure water. The choice of swab brand is important, and the chosen swabs were used for ion recovery studies from a porcelain surface, indicating that the use of moistened swabs that were previously washed provides greater recovery and less interference. An ion stability assay on swabs conducted over 12 weeks indicated that swabs should be stored in a refrigerator and analysed preferably within the first week after collection to minimize analyte loss. Background samples collected from an ATM did not show amounts of ions that could be confused with residues from explosions in most situations. The chromatographic and sampling methods were used in real samples of different types of black powder and residues from explosions of gunpowder contained in a “metalon” artifact and an ammonium nitrate emulsion, identifying the main ions from these materials and differentiating them.