Gunshot residue (GSR) refers to a conglomerate consisting of both organic molecules (OGSR) and inorganic species (IGSR). Historically, forensic examiners have focused only on identifying the IGSR particles by their morphology and elemental composition. Nonetheless, modern ammunition formulations and challenges with the GSR transference (such as secondary and tertiary transfer) have driven research efforts for more comprehensive examinations, requiring alternative analytical techniques. This study proposes the use of LC-MS/MS for chromatographic separation and dual detection of inorganic and organic residues. The detection of both target species in the same sample increases the confidence that chemical profiles came from a gun's discharge instead of non-firearm-related sources. This strategy implements supramolecular molecules that complex with the IGSR species, allowing them to elute from the column towards the mass spectrometer while retaining isotopic ratios for quick and unambiguous identification. The macrocycle (18-crown-6-ether) complexes with lead and barium, while antimony complexes with a chelating agent (tartaric acid). The total analysis time for OGSR and IGSR in one sample is under 20 minutes. This manuscript expands from a previous proof-of-concept publication by improving figures of merit, increasing the target analytes, testing the method's feasibility through a more extensive set of authentic specimens collected from the hands of both shooters and non-shooters, and comparing performance with other analytical techniques such as ICP-MS, electrochemical methods and LIBS. The linear dynamic ranges (LDR) spread across the low ppb range for OGSR (0.3-200 ppb) and low ppm range (0.1-6.0 ppm) for IGSR. The method's accuracy increased overall when both organic and inorganic profiles were combined.
Objective: The aim of this work was to assess the utility of the infrared camera as an effective tool for observing physical features like soot and gunshoot residues around the entrance hole, to aid estimation of the shooting distances on bloody, dark and patterned samples. Material and Methods: In this study, white control samples, as well as colored and patterned fabrics were fired from several distances (contact, 6 inches, 12 inches, 24 inches, and 36 inches). All shootings were performed with three replicates. Post-shooting infrared images were taken by use of Crime-lite 82S infrared, before and after application of blood on the samples. Human whole blood was sprayed onto the clothing by means of an aerosol spray bottle in two stages, and was partially dried before capturing the image with the infrared camera. Results: Using visual examination, it was not possible to detect any soot distribution on patterned fabrics, and the intensity of soot decreased and began to fade at 10 inches for other colored fabrics. The addition of blood to clothing masked the observation of iner soot and decreased the accuracy of the measurements. However, the soot was still visible when using an infrared camera on bloody samples, navy and black unknowns (10 inches) and patterned samples (contact and 6 inches), indicating the utility of an infrared camera on dirty and darker fabrics. Conclusion: The results of this study indicate that, similar to Modified Griess Test and Sodium Rhodizonate Test, soot alone is not the most accurate or reliable parameter for predicting true muzzle-to-target distance. However, an infrared camera enhanced the observation of presence of gunshoot residues not easily visible to the naked eye on dark, patterned and bloody samples. Thus, the proposed application of infrared imaging can easily be utilized as a complementary approach in the prediction of muzzle-to-target firing distance on dark, patterned and bloody fabrics.
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