Fast Mapping of Gunshot Residues by Batch Injection Analysis with Anodic Stripping Voltammetry of Lead at the Hanging Mercury Drop Electrode

Abstract

The forensic analysis of lead in gunshot residues (GSR) sampled on the hands of potential shooters is rendered faster, simpler and less expensive by a new batch injection analysis (BIA) method, based on differential pulse anodic stripping voltammetry (DPASV). A simple “J” shaped adaptor was designed to direct the flux of the analyte injected with a micropipettor onto the hanging mercury drop electrode of any commercial electrode stand. Sampling methods for GSR were compared and lifting with adhesive tape was elected for field use. The tapes are glued on polyethylene screens and stored in capped vials. Sampling with multiple strips provides coarse mapping of the distribution of lead on the shooter's hands. After a dissolution/extraction step with chloroform/aqueous 0.10 mol L−1 HCl, 100 μL of the aqueous phase are injected during 25 s for accumulation of lead on the HMDE at −0.60 V (vs. Ag/AgCl). A detection limit of 20 ng/mL of Pb(II), outreaching for GSR analysis, is reached without oxygen removal, at a frequency of 20 injections per hour. Results for sequences of shootings with a revolver and a pistol are presented.