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Forensic and environmental applications of flow injection separations of trace metals
Forensic scientists attempt to solve crimes through examination of the evidence found at crime scenes. By determining the relative concentrations of certain elements present in bullets, a profile of an individual sample can be developed that will allow investigators to match ammunition from a crime scene with that from a known source. The removal of a substantial proportion of the lead matrix is required for the determination of trace elements in bullets by inductively coupled plasma mass spectrometry (ICP-MS). ^ Several flow injection methods for the selective removal of lead from bullets have been developed. On-line solid-phase extraction with the commercially available resin Pb-Spec® removed the matrix quantitatively. Pb-Spec incorporates an immobilized crown ether, giving the resin selectivity for lead. The analytes were not retained, but passed through the column for quantification by ICP-MS. The method was validated by analyzing NIST SRMs 2415 (battery lead), 2416 (bullet lead), and 2417 (lead-based alloy). ^ The injection of large sample volumes into a flow injection ICP-MS system produces transient peaks with flat tops. The signal at peak maximum is directly proportional to analyte concentration. Sample throughput can be improved by making replicate measurements during the residence time at peak maximum instead of requiring multiple sample injections. A successful procedure utilizing Pb-Spec for the removal of matrix lead from a bullet sample was developed, and validated by the analysis of SRMs. ^ On-line precipitation and filtration of the matrix was examined. The bullet sample was combined with sulfuric acid, and the conditions for maximum precipitation were obtained. The resultant lead sulfate was filtered on a column packed with macerated glass wool. The formation of sulfates by the analytes was not favored, so they were detected by ICP-MS. ^ The potential for lead preconcentration by Pb-Spec was investigated with environmental water samples, and the retention characteristics were examined in detail. ^ The feasibility of incorporating a crown ether-containing supported liquid membrane into a flow injection manifold was investigated for the removal of high concentrations of lead from solutions. Experimental and theoretical results demonstrated that the time scale of mass transfer was too slow for flow injection applications. ^
Emily Ruth Yourd,
"Forensic and environmental applications of flow injection separations of trace metals"
(January 1, 2003).
Doctoral Dissertations Available from Proquest.