Forensic ballistics by inductively coupled plasma-optical emission spectroscopy: Quantification of gunshot residues and prediction of the number of shots using different firearms

A new analytical method is proposed for the Pb, Ba and Sb quantifications on gunshot residues (GSR) from firearms using inductively coupled plasma optical emission spectrometry (ICP OES). Lead (Pb), barium (Ba) and antimony (Sb) concentrations in GSR from .38 revolver and .380 and .40 caliber pistols were determined as function of number of shots (from 1 to 5 for the .38 revolver and from 1 to 10 for the pistols) and multiple linear regression model was constructed to determine the number of shots. Also, the sensitivity of ICP OES was compared to conventional colorimetric test in function of distance of shooting (from 0 to 200 cm). Analyzing the effect of distance of shooting over the GSR concentration, the colorimetric test evidenced the presence of a red-pink color only at short distances (from 0 to 10 cm), thus indicating the presence of Pb. For ICP OES analyses, the two analytical methodologies employed presented higher sensitivity than the colorimetric assay, where Pb, Ba and Sb are found from 0 cm ([Pb] = 3158.63 μg L− 1; [Ba] = 85.33 μg L− 1; and [Sb] = 104.90 μg L− 1) to 200 cm ([Pb] = 81.52 μg L− 1; [Ba] = 20.20 μg L− 1; and [Sb] = 8.32 μg L− 1) for the extraction using digestion by microwave. For analyses of GSR using different firearms, good linear correlation coefficients (R2 > 0.97) were observed between the GSR concentration and the number of shots. Therefore, it was possible to predict the number of shots with good accuracy from Pb, Ba and Sb concentrations using .38 revolver and .40 and .380 caliber pistols. Furthermore, the GSR concentration from different firearms, increased in the following order: .40 pistol > .380 pistol > 38 revolver.