Separation and identification of anions using porous graphitic carbon and electrospray ionization mass spectrometry: Application to inorganic explosives and their post blast residues

Abstract

Identification of the anions in inorganic explosives and their post-blast residues using ion chromatography (IC) and/or capillary electrophoresis (CE) is well established. However, IC and CE instrumentation are not as common in forensic science laboratories. Furthermore, coupling IC and CE to a mass spectrometer can be challenging as volatile buffers are required or ion suppressors must be used. Porous Graphitic Carbon (PGC) is a relatively new stationary phase type that is available for High Performance Liquid Chromatography (HPLC). PGC is known for its high retention of polar species and separation of anions using PGC has been demonstrated. In this work, a PGC (2.1 × 100 mm) column was coupled to an electrospray ionization mass spectrometer (ESI-MS) for the analysis and detection of anions. Several parameters of the method were optimized including ion source temperature (550 °C), MS cone voltage (75 V), injection volume (1 μL), solvent composition (1% formic acid in water), and column temperature (80 °C). This resulted in a method that separated 6 anions Cl⁻, NO₃⁻, ClO₃⁻, HSO₄⁻, ClO₄⁻, and dicyandiamide (DCDA) in less than 5 min. Several low explosive powders were analyzed intact and after burning. Finally, the post-blast residues of two black powder substitutes were extracted from pipe bomb container fragments and analyzed using this technique.