Comparison of portable and benchtop electrochemical instruments for detection of inorganic and organic gunshot residues in authentic shooter samples

Abstract

Analysis of gunshot residue currently lacks effective screening methods that can be implemented in real time at the crime scene. Historically, SEM-EDS has been the standard for analysis; however, advances in technology have brought portable instrumentation to the forefront of forensic science disciplines, including the screening of GSR. This study proposes electrochemical methods with disposable screen-printed carbon electrodes for GSR screening at the laboratory and points of care due to their rapid, cost-efficient, and compact platform. GSR residues were extracted from typical aluminum/carbon adhesive collection stubs and analyzed via square-wave anodic stripping voltammetry. Benchtop and portable electrochemical instruments were compared for the assessment and classification of authentic shooter samples by monitoring a panel of inorganic and organic GSR elements and compounds including lead, antimony, copper, 2,4-dinitrotoluene, diphenylamine, nitroglycerin, and ethyl centralite. The evaluation included the assessment of figures of merit and performance measures from quality controls, nonshooter, and shooter data sets. Samples collected from the hands of 200 background individuals (nonshooters), and shooters who fired leaded ammunition (100) and lead-free ammunition (50) were analyzed by the benchtop and portable systems with accuracies of 95.7% and 96.5%, respectively. The findings indicate that electrochemical methods are fast, sensitive, and specific for the identification of inorganic and organic gunshot residues. The portable potentiostat provided results comparable with the benchtop system, serving as a proof-of-concept to transition this methodology to crime scenes for a practical and inexpensive GSR screening that could reduce backlogs, improve investigative leads, and increase the impact of gunshot residues in forensic science.

Should Inorganic or Organic Gunshot Residues Be Analysed First?

“…7). NG constitutes a large proportion of the ammunition since it is one of the primary explosives used in ammunition [29,46,51]. Detected concentrations were not significantly different between the two protocols (Tables 7 and 8 left).…”

Strategies for assessing the limit of detection in voltammetric methods: comparison and evaluation of approaches

“…Lead and DPA were prepared together as previously reported. 25,26 Briefly, an aliquot of the DPA standard was evaporated under air and then reconstituted using acetate buffer and a diluted aliquot of the lead standard to generate a sample containing 4 µg mL −1 lead and 16 µg mL −1 DPA. This solution was serially diluted to yield samples containing 2 µg mL −1 Pb + 8 µg mL −1 DPA, 1 µg mL −1 Pb + 4 µg mL −1 DPA, 0.5 µg mL −1 Pb + 2 µg mL −1 DPA, 0.25 µg mL −1 Pb + 1 µg mL −1 DPA, and 0.125 µg mL −1 Pb + 0.5 µg mL −1 DPA.…”

“…Square-wave anodic stripping voltammetry (SWASV) was utilized to analyze GSR-related compounds, Pb and DPA. The method parameters were employed based on Dalzell et al 26 and were as follows: deposition potential −950 mV, deposition time 120 s, starting potential −1000 mV, ending potential +1200 mV, potential step 5 mV, amplitude 25 mV, frequency 11 Hz. The deposition stage serves as a pre-concentration stage prior to the square-wave sweep.…”

Voltammetric analysis of luminescent markers in gunshot residues

“…New methods and methodologies have been proposed to improve gunshot residue analysis. SWV has been used to detect organic and inorganic GSR compounds [26].…”