As gun-related crimes become more widespread, gunshot residue (GSR) has become an important part of these investigations. It is generally collected with an aluminum stub coated in adhesive which is then directly analyzed using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM-EDX). Traditionally, GSR is confirmed by the presence of barium, antimony, and lead. However, new ammunition has been introduced on the market that is lead or heavy metal free. This coupled with the fact that not all three components are always found when collecting GSR has prompted for the development of a technique that analyzes organic gunshot residue (OSGR) as well as the original three elements that comprise inorganic gunshot residue (IGSR).
Organic GSR can come from different sources such as the propellant powder and primer and can be classified as explosives or additives. They are common among ammunition and can be detected on the hands many hours after firing a weapon. Because of this, a new method of analyzing both OGSR with IGSR can strengthen evidence value if both are found.
Two different extraction protocols were developed. Protocol 1 used alcohol swabs followed by liquid extraction. Protocol 2 used aluminum stubs coated with double sides carbon tape followed by liquid extraction. Samples were then analyzed using ultrahigh-performance liquid chromatography (UHPLC) coupled with triple quadrupole-tandem mass spectrometry (QQQ). To simulate a case scenario, firearms were discharged at a firing range. Samples were taken pre- and post-discharge for controls and samples, respectively.
The two protocols were compared for which components of OGSR were found in the highest quantities and for which extraction protocol was most effective. DPA and TNT were two of the highest recovered in Protocol 1, and PETN and TNT were two of the highest recovered in Protocol 2. Protocol 2 achieved the greatest extraction results. The study concluded that GSR stubs analyzed with SEM-EDX followed by liquid extraction and UHPLC analysis worked best.
Taudte, Regina Verena, Claude Roux, Lucas Blanes, Mark Horder, K. Paul Kirkbride, and Alison Beavis. “The Development and Comparison of Collection Techniques for Inorganic and Organic Gunshot Residues.” Anal Bioanal Chem Analytical and Bioanalytical Chemistry 408.10 (2016): 2567-576. Web.
Forensic Summary by Gina Gallucci