Proposed practices for validating the performance of instruments used for automated inorganic gunshot residue analysis

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

“…Innovations in instrument technology, automatisation of analysis, improvements in image processing and EDS spectra treatment software, as well as statistical approaches enlarged the possibility of SEM/EDS analysis and significance of interpretation of the obtained data [3,4]. However, strict monitoring of instrument sub-system performance and method validation to demonstrate the whole system behavior needed in order to guarantee the reliability of inorganic gunshot residue (iGSR) results presented in front of the justice authorities [13]. Brozek-Muncha [6] demonstrated that SEM/EDS data could be used more comprehensively for study the relationship between chemical and morphological properties of GSR particles, source and mechanism of their formation.…”

“…A standard sample Plano SPS-5P-2A, originated from the proficiency testing GSR 2005 PT by ENFSI GSR 2005 PT [14] was used as a positive control. In order to assure minimal rate of false negative results and to control the optimal instument operating parameters [13], the positive control sample was scanned before each sample till at least one particle, containing PbBaSb with a dimeter 1 µm was identified. Blank sample was used to monitor laboratory environment or cross-contamination and to asure minimal rate of FP results.…”

“…Blank sample was used to monitor laboratory environment or cross-contamination and to asure minimal rate of FP results. Additionally, for EDS detector quality control Cu Kα Centroid 8.04 ± 0.03 and Al Kα Centroid 1.48 ± 0.03 were used to adjust known peaks at correct positions [13].…”

“…It is well known that working parameters of SEM/EDS instrument affect the total number of detected GSR particles and therefore, should be carefully studied and optimized for each instrument and laboratory needs [4]. A detailed systematic guide for testing SEM/ EDS behavior and identifying possible misbehavior of instruments' sub-systems have been recently proposed [13]. EURACHEM guide 2014 presents general rules for method validation and recommends field specific guidelines to be followed [12].…”

“…Increasing reliability of SEM/EDS analysis and reducing false positive (FP) and false negative results are connected to the possibility for revisit the specific or suspicious particles after automatic identification and re‐study particle morphology and elemental composition [4,5]. When an evidence from shooting event is presented as characteristic GSR particle, attention must be paid to the analytical characteristics of the applied SEM/EDS protocol and quality control procedures after method validation [12–14]. It is well known that working parameters of SEM/EDS instrument affect the total number of detected GSR particles and therefore, should be carefully studied and optimized for each instrument and laboratory needs [4].…”