Identificação sequencial de resíduos de disparo de arma de fogo por LC-MS e ICP-MS

Abstract

Determining shooters through expert analysis is of extreme legal importance, as this is how experts help clarify crimes committed with the use of firearms. Therefore, it is essential to develop methodologies for analyzing gunshot residue (GSR) to determine shooters. In this work organic GSR (oGSR) were analyzed in gunpowder samples directly and non-destructively for the first time by low temperature plasma coupled to mass spectrometry (LTP-MS) using a heated sample holder for better desorption of the analytes. Ethylcentralite - EC (m/z 269), Diphenylamine - DPA (m/z 170), and Dimethylphthalate - DMP (m/z 163) were identified in the four gunpowder samples analyzed, with the best intensity at the temperature of 120 °C in the holder. sample. In the ESI-MS (Electrospray Ionization Coupled to Mass Spectrometry) spectra of the gunpowder solutions tested, these ions were not detected, indicating that the LTP heating methodology offers clear advantages over more traditional approaches, something that is interesting in analysis. forensics, due to the need for rapid analysis and preservation of the sample as counter-evidence. For samples collected by swabs from shooters' hands, an efficient methodology for the collection and sequential analysis of oGSR and inorganic GSR (iGSR) by LC-MS and ICP-MS was developed from a single sample. Two types of sample collection from shooters' hands were evaluated, dry swab and ethanol swab. The results showed no statistical difference between the two collections, so the dry swab collection was chosen due to its greater simplicity. Samples were collected with a dry swab (5 shooters, triplicate, .38 caliber revolver, and .40 caliber pistol at different collection times 0 h, 30 min, 1 h, 2 h, 3 h, and 4 h) to create a model supervised classification using the SIMCA method. The results showed 90% sensitivity, that is, the ability to identify a non-shooter sample. No differences were observed in the amounts of GSR for shots with revolvers and pistols, and shots fired by left-handed people. Large variations in GSR concentrations were observed and it was not possible to correct for such variations by correcting the GSR concentration divided by the shooters' hand area. This study contributes to advancing the understanding of GSR analysis, providing solid foundations for forensic applications, with potential impact on the elucidation of criminal events.