Gunshot residue and gunshot residue-like material analysis using laser ablation inductively coupled plasma mass spectrometry imaging

Abstract

This work aims to develop a method based on the tape-lift collection and Laser Ablation combined to Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) measurements for Gunshot Residue (GSR) to be useful in forensic analysis. The most widely used method is the Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy (SEM-EDS); still, it has some disadvantages, such as long-time analysis. Thus, other analytical techniques have been used, such as LA-ICP-MS, since the GSR normally contain Pb, Ba, and Sb (together). The corresponding signals can be measured at the same ablation time, making it possible to obtain images of elemental distribution that can be overlaid to show the presence of GSR. It is well known that these elements have several commercial and industrial applications. Therefore, due to the similar composition and formation conditions, residues from other sources, such as fireworks, brake pads, airbags, and lighters can be confused with GSR, emphasizing the importance of its discrimination. To distinguish between real GSR and GSR-like residues, samples of five shooters and fifteen non-shooters were collected using a carbon adhesive tape (stub) by pressing it on the surface of the hands. Non-shooters samples were composed of brake pad mechanic's workers, people after using fireworks, and people who had never fired a gun (blanks). The images of elemental distribution were obtained using MATLAB™, resulting in a clear visual difference between the images from shooters and non-shooters samples. Ternary graphs were obtained using ORIGIN™ for each kind of sample, revealing a grouped distinctive distribution for the different GSR-like sources, demonstrating the ability of the developed method to discriminate GSR against a possible false positive. The developed method provided a discrimination between samples of shooters and non-shooters, by comparing their images of elemental distribution, without previous sample preparation and with an analysis time of 33 min.