Characterization of industrial explosives based on the determination of metal oxides in the identification particles by microwave digestion and atomic absorption spectrometry method

Identification particles used for the purpose of the post-blast identification of explosives have a coding system based on the combination of metal oxides and their various concentrations. These materials are composed of the polymeric matrix, iron powder (ferromagnetic properties), UV light active dyestuff and various metal oxides in a various ratios. A suitable analytical method has to be used for an accurate characterization of these metal components in the particles in order to find the required information, i.e. to determine the place and the year of production and as the case may be, also the production batch of misused explosives. In this work, the method of microwave digestion and flame atomic absorption spectrometry (F-AAS) was developed for an accurate determination of Zn, Mg, Cu and Pb in a few novel types of identification particles and applied to their characterization. When using specific sample treatment (digestion with a mixture of nitric acid with hydrochloric or hydrofluoric acid), the 3σ limits of detection (LODs) for the determination of Zn, Mg, Cu and Pb in 5 mg original samples were 1.9, 0.2, 1.3 and 2.4 mg g−1, respectively. The signal suppression due to the presence of HNO3 + HCl or HNO3 + HF was observed for Zn; therefore, the calibration solutions had to be prepared exactly with the same acids as those used for the sample mineralization. The determination of Mg, Cu and Pb was free of interferences; hence a simple calibration curve method could be adopted for attaining accurate results. The accuracy was checked by comparison of the results with those obtained by means of independent inductively coupled plasma optical emission spectrometry (ICP-OES). Good precision values, as relative standard deviation, in the range of 1–5% were obtained. A total number of 71 samples was analysed and classified by multivariate methods to prove the suitability of the procedure proposed for the purpose of the identification of explosives.