A study of the effect of working parameters and validation of SEM/EDS method for determination of elemental composition of commonly encountered GSR samples in shooting events in Kosovo

Reliability of forensic evidences for presence of inorganic gunshot residue (iGSR) on a given surface strongly depends on the performance of scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) method. This article presents the results from a study of the effect of SEM/EDS working parameters on the method performance and quality of iGSR data, as well as a development of a database of iGSR encountered in R Kosovo. The optimal working parameters of SEM/EDS were established by one-variable-at-a-time approach and the method was validated according to ASTM1588-10. The precision, trueness, and expanded uncertainty for PbBaSb particles were estimated and the method was assessed as a "fit for purpose" with a satisfactory performance (z-score < 2). Expended uncertainty of quantification of GSR particles estimated by single laboratory and quality control approach was 6% (k = 2). The validated SEM/EDS method was applied for identification of characteristic iGSR particles in samples from shooting events in Kosovo. The method was demonstrated to be capable of providing a legal proof for iGSR existence on a specific surface. The quality of the results was not influenced by the origin of iGSR. Five hundred fifty-five samples from 144 cases occurred during the last 3 years were analyzed and 14% rate of positive results was found.