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 shooters hands. After a dissolution/extraction step with chloroform/aqueous 0.10 mol L À1 HCl, 100 mL of the aqueous phase are injected during 25 s for accumulation of lead on the HMDE at À 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.

A batch injection analysis (BIA) system, which uses an automatic mercury electrode (AME) as an amperometric detector, is described. The capillary of this AME was adapted in an inverted position through the bottom of a simple cylindrical electrochemical cell, in order to generate more stable sessile drops and to grant free access for the tip of the programmable micropipettor. The BIA system was evaluated by using the electrochemical oxidation of L-ascorbic acid to dehydroascorbic acid on the sessile mercury drop electrode. Acetate buffer solution (50 mM, pH 4.8) was used as supporting electrolyte. The working electrode was operated at 0.230 V (vs. Ag/AgCl). The effect of the dispensing rate, of the dispensed volume, of the distance between the mercury drop and the pipettor tip, as well as of the solution level in the cell were evaluated. Injections of 50 mL were suitable to reach a detection limit of about 2.5 mM (450 ppb). At the 50 mM ascorbic acid level, an RSD of 1.6 % (N 35) was observed with or without mercury drop renewal between injections. A frequency of 300 injections per hour may be reached when the drop is renewed sporadically. The new BIA method was applied to the determination of ascorbic acid in packedacanned tropical fruit juices. Selectivity was granted by differential measurements of the peak current before and after exposure of samples to ascorbate oxidase (from cucumber).

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Aos meus amigos Marcelo (ao qual não me referirei aqui como Pompom, pois ele iria ficar bravo!...), Gt Andy Cavicchioli, Renato e Beirute (também conhecido, porém por poucos, como Fabiano), pelo apoio, carinho e amizade sincera sempre. Ao Flávio because di quê tenho grande respeito e admiração. Ao Eduardo pela ajuda sempre e ao Carlos, pelas fotos contidas nesta dissertação. A todo pessoal do laboratório, pelo ambiente divertido: