Abstract
The investigation of inorganic gunshot residues (iGSR) is to detect particles containing antimony (Sb), barium (Ba), and lead (Pb) on a sample via either destructive or non-destructive techniques. Laboratory competence on iGSR analysis is assessed via successful participation in proficiency testing (PT). According to ISO 13528 Section 11.1, PT schemes can be recognized by examination under sample’s magnitude and investigation of its properties. Two types of PT scheme for iGSR analysis are carried out. In the first type (I-iGSR PT), participants are requested to submit the GSR results with quantitative information. For the second type (II-iGSR PT), participants shall report the presence of characteristic iGSR particles on PT sample. However, to avoid wasting budget and excessive efforts, selection of PT type can be considered from actual performance in each laboratory method. In this study, the Royal Thai Police cooperated with laboratory network to propose a quick guide for performance assessment of scanning electron microscope with energy dispersive x-ray spectrometer (SEM/EDS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) using standard deviation index (SDI). The difference between the mean of iGSR sample and inter-laboratory were compared. The results revealed that SDI values were employed to evaluate SEM/EDS or ICP-OES performance in both types of iGSR PT programs. The SDI value can be used as a quick estimation before PT operation. The near zero SDI of PT sample indicated that it is eligible for all iGSR types, whereas the SDI above 1 only suggested for qualitative analysis PT. Hence, the observed SDI values can be used as a tool for instrument performance assessment and iGSR analysis decision prior to PT subscription for the first or next rounds.