Electroanalysis of ethyl-centralite propellant stabiliser at magnetic nanoparticle modified glassy carbon and screen-printed electrodes with extension to forensic firearm residue analysis

Electroanalysis of organic residues of the propellant stabiliser ethyl-centralite (1,3 diethyl-1,3 diphenyl urea, EC) generated from the discharge of a weapon or improvised explosive devices is examined. Comparative effects of an electrode modifier, nanoparticles of magnetite (Fe3O4), on the sensor performance was of interest, with customised printed prototype development and analysis of organic firearm residue (OFAR) samples. Differential pulse voltammetry (DPV) calibration studies realised sensitivity of 6.37×10-2 μA∙μM-1 (over the concentration range 2.5-50 μM) at the magnetic nanoparticle modified electrode, representing a 1.65 fold signal increase relative to unmodified electrodes with limit of detection 4.39 µM. Inclusion of the OFAR co-existing diphenylamine (DPA) stabiliser realised signal discrimination and sensitivity of 7.49×10-2 and 5.49×10-2 μA∙μM -1 for DPA, and EC respectively, using DPV over the same range. The work culminated in the qualitative and quantitative analysis of propellant stabilisers in firearm residue acquired from a single base shotgun shell, with recovery from a target sample cloth, together with unburnt propellant, making promising first steps towards a customised screen-printed prototype for use by forensic professionals. Scanning electron microscopy/energy dispersive spectroscopy and atomic force microscopy were employed for particle confirmatory analysis.