Identification and determination of inorganic anions in real extracts from pre- and post-blast residues by capillary electrophoresis

Fast, selective, and sensitive analysis of inorganic anions is compulsory for the identification of explosives in post-blast or environmental samples. For the last twenty years, capillary electrophoresis (CE) has become a valuable alternative to ion chromatography (IC) for the analysis of inorganic-based explosives because of its low running costs and its simplicity of use. This article focuses on the development and validation of a CE method for the simultaneous analysis of 10 anions (chloride, nitrite, nitrate, thiosulphate, perchlorate, chlorate, thiocyanate, carbonate, sulphate, and phosphate) which can be found in post-blast residues, plus for the first time azide anion, possibly present in the composition of detonators, and the internal standard (formate) in 20 min total runtime. Intermediate precisions were 2.11% for normalized areas and 0.72% for normalized migration times. Limits of detection close to 0.5 ppm for all anions were obtained with the use of preconcentration techniques, thanks to a fast and simple sample preparation allowing the analysis of a large variety of matrices with the developed generic CE method. The matrix effects were statistically studied for the first time in the explosive field for different matrices, containing interfering anions and cations, sometimes at high levels. In fact, no significant matrix effect occurred (tests with blank matrix extracts of soil, cloth, glass, plastic, paper, cotton, and metal). Finally, analyses of real post-blast residues and real detonator extracts were performed. The CE results were compared with those obtained with the IC method used routinely and showed excellent correlation.