Análise de íons inorgânicos em resíduos de explosão utilizando microssistemas eletroforéticos

Abstract

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (MSE) devices integrated with capacitively coupled contactless conductivity detection (C4D) for the separation and detection of inorganic anions in post-blast explosive residues. The best separation condition was achieved using a running buffer composed of 35 mmol L-1 lactic acid, 10 mmol L-1 histidine and 0.070 mmol L-1 cetyl(trimethyl ammonium) bromide. For C4D measurements, the highest sensitivity was obtained applying a 700 kHz sinusoidal wave with excitation voltage of 20 Vpp. The separation of Cl-, NO3-, NO2-, SO42-, ClO4- and ClO3- was performed within ca. 150 s with baseline resolution and efficiencies between 4.4x104 and 1.7x105 plates/m. The found limits of detection ranged between 2.5 and 9.5 μmol L-1. Also, excellent repeatability was obtained, with relative standard deviation lower than 0.8%, 8.8% and 13.5% for the injection time, for the intensity and the peak areas, respectively. Lastly, real samples of post-blast explosive residues were analyzed on the MSE-C4D devices obtaining successfully the determination of Cl-, NO3- and SO42-. The achieved concentration values varied between 2301,610 µg g-1 for Cl-, 805,490 µg g-1 for NO3- and 1453,270 µg g-1 for SO42-. It was also possible to compare the anionic profile of residues of an improved explosive device and a commercial explosive emulsion, confirming the improved explosive device composition, based on ammonium nitrate fuel oil (ANFO). The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the MSE-C4D devices emerge as a powerful and portable analytical platform for on-site analysis demonstrating to be a promising tool for the crime scene investigation.