Orthogonal Identification of Gunshot Residue with Complementary Detection
Principles of Voltammetry, Scanning Electron Microscopy, and Energy-Dispersive
X‑ray Spectroscopy: Sample, Screen, and Confirm
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Abstract
Field-deployable
voltammetric screening coupled with complementary
laboratory-based analysis to confirm the presence of gunshot residue
(GSR) from the hands of a subject who has handled, loaded, or discharged
a firearm is described. This protocol implements the orthogonal identification
of the presence of GSR utilizing square-wave stripping voltammetry
(SWSV) as a rapid screening tool along with scanning electron microscopy
(SEM) and energy dispersive X-ray spectroscopy (EDX) to confirm the
presence of the characteristic morphology and metal composition of
GSR particles. This is achieved through the judicious modification
of the working electrode of a carbon screen-printed electrode (CSPE)
with carbon tape (used in SEM analysis) to fix and retain a sample.
A comparison between a subject who has handled and loaded a firearm
and a subject who has had no contact with GSR shows the significant
variations in voltammetric signals and the presence or absence of
GSR-consistent particles and constituent metals. This initial electrochemical
screening has no effect on the integrity of the metallic particles,
and SEM/EDX analysis conducted prior to and postvoltammetry show no
differences in analytical output. The carbon tape is instrumental
in retaining the GSR sample after electrochemical analysis, supported
by comparison with orthogonal detection at a bare CSPE. This protocol
shows great promise as a two-tier detection system for the presence
of GSR from the hands of a subject, whereby initial screening can
be conducted rapidly onsite by minimally trained operators; confirmation
can follow at the same substrate to substantiate the voltammetric
results