Proficiency Testing of Inorganic Gunshot Residue Analysis for Laboratory Performance Assessment

In forensic examination, inorganic gunshot residue (iGSR) can potentially refer to the act of shooting from a person and become value case evidence. The iGSR analysis is performed by the detection of particles containing antimony (Sb), barium (Ba), or lead (Pb) in a sample. For reliable evidence examination, laboratory competence for the iGSR analysis can be evaluated via the proficiency testing (PT). PT schemes can be achieved by examination of sample magnitude and properties while the iGSR analysis is targeted for quantitative information or characteristic iGSR particles obtained from PT samples. In this study, the Royal Thai Police aims to perform the assessment in comparison with interlaboratory and propose a quick guide to assess the iGSR analysis based on forensic examination techniques, scanning electron microscope with energy dispersive X-ray spectrometer (SEM/EDS) and inductively coupled plasma optical emission spectrometry (ICP OES). Standard deviation index (SDI) was employed for the performance assessment. The differences in the interlaboratory results were compared. The nearly zero SDI indicated optimal readiness for both schemes of iGSR analysis. While standard guidelines accept an absolute SDI up to 2, we propose a preliminary internal guideline wherein an absolute SDI above 1 cautiously suggests restricting the laboratory to qualitative-only PT participation. The observed SDI values can be used as a tool for performance assessment and decision making prior to PT subscription of iGSR analysis. Therefore, quick evaluation offers the benefit of time saving and budgets on PT process for each laboratory under the forensic unit in terms of laboratory performance.