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Fast identification of inorganic and organic gunshot residues by LIBS and electrochemical methods

NCJ Number
Forensic Chemistry
Date Published

In this study, electrochemical and laser-based spectroscopic methods (LIBS) are proposed as screening methods that are quicker, more selective and more effective than any current field-testing technique.



These methods offer superior information by simultaneous detection of organic and inorganic gunshot residues, including a substantial number of elements used in modern ammunition. Moreover, the selected analytical scheme permits subsequent confirmatory analysis (SEM-EDS) on the same sample. The rapid scanning of the laser-beam favors the identification of up to 5 different emission lines per target element in less than one minute, with repeatability better than 11% RSD and limits of detection for the species of interest in the range of 0.2–200 ng. Optimization of the electrochemical sensors demonstrated the feasibility of Square Wave Anodic Stripping Voltammetry (SWASV) for the rapid detection of inorganic and organic target compounds using carbon printed disposable electrodes (repeatability less than 8% RSD, detection limits 0.1–1 ng/µL, linearity > 0.991). The separation and detection of mixtures of Pb, Sb, Cu, DNT, and NG was possible after LIBS analysis, in approximately 3 min per sample. A set of 112 samples, 20 samples from non-shooters and 92 samples from 28 shooters, were collected as part of the validation study. Pistol (9 mm and .22) and revolver (.357 Magnum) were fired at indoor and outdoor shooting ranges. Metrics of performance, such as error rates (false positives and false negatives), specificity, sensitivity, and accuracy, indicate the combination of LIBS and electrochemical methods are a reliable and promising approach to advance current practice. (Publisher Abstract)