DETERMINATION OF TRACE IMPURITIES IN LEADSHOTGUN PELLETS BY GRAPHITE-FURNACE AAS

For the purpose of forensic characterization of lead shotgun pellets, a rapid and highly sensitive method for analysis of impurities is requ ired. Graphite furnace AAS is such a method. Copper, silver and arseni c impurities in lead were measured by direct introduction of the sampl e solution into a graphite furnace. For solutions with a high concentr ation of lead, a matrix modifier was required and the absorbance of ea ch element depended on the ashing temperature. In accordance with the results of experiments to find the optimum analytical conditions, nick el was used as the most suitable matrix modifier for arsenic, and appr opriate ashing temperatures were determined for each element. Sample p ieces were cut from the lead pellets and 10 mg was dissolved in 2 ml o f (1:1) nitric acid by heating at 60-degrees-C for 1 h. After the solu tion was diluted to 10 ml with distilled water, 10 mul of this solutio n was introduced into the graphite furnace. For the measurement of ars enic, 10 mul of 100 mug ml-1 nickel solution was introduced simultaneo usly as a matrix modifier. The operating conditions of the graphite fu rnace were as follows: drying, at 95-degrees-C for 40 s; ashing, coppe r at 500-degrees-C for 8 s; silver at 400-degrees-C for 8 s; arsenic a t 1000-degrees-C for 8 s, atomizing, copper at 2500-degrees-C for 5 s; silver at 2000-degrees-C for 5 s; arsenic at 2600-degrees-C for 5 s. This method was applied to two NIST standard samples, No. 1132 and C24 16, and nine shotgun pellet samples. The analytical results for the st andard samples were in good agreement with the certified values. Compa rison of the impurities measured by this method allows us to identify shotgun pellets of the same origin. This is because the impurity conte nt showed large variations between shotgun pellet samples from differe nt manufacturers.