Analysis of Inorganic GSR Microparticles Using Laser Induced Breakdown Spectroscopy (LIBS)

Emily Heller*, Korina Menking-Hoggatt, Claudia Martinez-Lopez and Tatiana Trejos, Department of Forensic and Investigative Science, West Virginia University, Morgantown, WV 26505

Field (Broad Category): Forensics (Physical Sciences & Engineering) 

Student’s Major: Forensic Chemistry 

Firearms-related investigations require fast, reliable, and sensitive analysis of gunshot residue (GSR) evidence. However, current standard methods are time-consuming and costly technique that is further challenged by new types of modern ammunition that lack characteristic GSR markers. Even more challenging is the lack of standard reference materials to assist in research and development of new methods. In this study we propose a rapid alternative method of analysis using Laser-Induced Breakdown Spectroscopy (LIBS), which provides multi-elemental characterization of inorganic GSR (IGSR) with minimal sample destruction. Analysis by LIBS was performed on twenty IGSR micro-particle standard solutions created in-house at Dr. Trejos’ research group. The micro-IGSR standards were previously characterized qualitatively, quantitatively, and morphologically by two other analytical techniques (SEMEDS and ICP-MS) and, therefore, served as controls for method optimization and cross-validation. The samples were analyzed by a LIBS microchemical mapping method that provided elemental analysis and spatial information. The LIBS method successfully identified the main standard IGSR markers: lead, barium, and antimony, in addition to other elements in lead-free ammunition (e.g., Al, Cu, K, Ti, Zn). An agreement of elemental composition was observed across all analytical techniques, demonstrating the utility of LIBS for IGSR detection. One advantage of LIBS over SEM-EDS and ICP-MS is its speed, where a typical analysis takes 1.5 minutes per sample, as opposed to 8 hours per sample by SEM-EDS or 3-5 hours by ICP-MS. The study demonstrates LIBS potential of becoming a rapid and accurate screening method for GSR analysis. 

Funding: 

Program/mechanism supporting research/creative efforts: WVU 497-level course