Gunshot residues (GSR) analysis of clean range ammunition using SEM/EDX, colorimetric test and ICP-MS: A comparative approach between the analytical techniques

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful tool for a rapid analysis of chemical elements due to its high sensitivity, selectivity and multi-elemental character. Herein, the ability of the ICP-MS technique is evaluated to determine the gunshot residues (GSR) from clean range ammunition using a 0.40 caliber pistol and a 0.38 caliber revolver as a function of number of shots (n=1–7 shots for the pistol and n=1–5 shots for the revolver). The GSR was collected on the two regions of right and left hands: thumb and forefinger palm and thumb and forefinger back. ICP-MS results were compared to classical techniques in the forensic ballistics: the colorimetric test using sodium rhodizonate reagent and scanning electron microscope with energy dispersive X-ray spectrometry (SEM/EDX). Negative results were found for Pb and Ba using the colorimetric test from GSR with n=7 shots from 0.40 caliber pistol. For SEM/EDX analysis, photomicrographs show indefinite morphology for the GSR of clean range ammunition, in contrast to reported by conventional GSR. Moreover, the EDX results primarily identified C, O, K, Al, S, Si, Cu, Zn, Ti, Cr, Cl, Mo, Sr, and Fe. Differently, ICP-MS provided positive results for Pb, Ba and Sb, with maximum concentrations of 4.20μg·L−1, 10.9μg·L−1 and 0.119μg·L−1, respectively, as well as for Al, Ti, Cr, Mo, Cu, Zn and Sr. Finally, Al, Zn, Cu and Sr can be used as new markers of GSR of clean range ammunition, since they are the most abundant species detected.