Detection of inorganic gunshot residue elements in firearms using laser-induced breakdown spectroscopy

In this study, laser-induced breakdown spectroscopy (LIBS) has been used to identify the elements present in the gunshot residue (GSR) sample collected from firearms. If multiple elements are present in the sample, conventional LIBS qualitative analysis is time-consuming and there is a probability of making error in elemental identification due to overlapping of closely spaced emission lines of different elements. Hence, we used a simulation-based approach to determine the elemental composition of the sample considering laser-produced plasma to be in local thermodynamic equilibrium (LTE) and compared the simulated spectrum with experimentally obtained spectrum to affirm the presence of particular elements. Sample of GSR was collected in pristine cotton from the barrel of three different firearms which used different cartridges for firing. LIBS could detect elements other than characteristic elements of GSR. We also confirmed the presence of these elements using energy dispersive X-ray spectrometry (EDX). The portability advantage of LIBS, along with the simulation method makes it possible to examine GSR samples directly at the scene of crime which would save time and the sample can be examined without any contamination. This study demonstrated an easy and efficient way of examining GSR sample which facilitates fast and accurate resolution of firearm-related crimes.