Rapid separation of post-blast explosive residues on glass electrophoresis microchips

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C⁴ D) 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 lactic acid, 10 mmol/L histidine and 0.070 mmol/L cetyl(trimethyl ammonium) bromide. For C⁴ D measurements, the highest sensitivity was obtained applying a 700 kHz sinusoidal wave with excitation voltage of 20 V_pp . The separation of Cl^- , NO₃^- , NO₂^- , SO₄^2- , ClO₄^- and ClO₃^- was performed within ca. 150 s with baseline resolution and efficiencies between 4.4 × 10⁴ and 1.7 × 10⁵ plates/m. The found limits of detection ranged between 2.5 and 9.5 μmol/L. Last, real samples of post-blast explosive residues were analyzed on the ME-C⁴ D devices obtaining successfully the determination of Cl^- , NO₃^- and SO₄^2- . The achieved concentration values varied between 12.8-72.5 mg/L for Cl^- , 1.7-293.1 mg/L for NO₃^- and 1.3-201.3 mg/L for SO₄^2- . The data obtained using ME-C⁴ D devices were in good agreement with the concentrations found by ion chromatography. The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the ME-C⁴ D devices emerge as a powerful and portable analytical platform for on-site analysis demonstrating to be a promising tool for the crime scene investigation.