On-line matrix removal of lead for the determination of trace elements in forensic bullet samples by flow injection inductively coupled plasma-mass spectrometry

The determination of trace elements in lead by inductively coupled plasma (ICP) source mass spectrometry (MS) is not possible without the removal of a substantial proportion of the lead matrix. This was achieved by the retention of lead from a 130-mul sample solution (100 mg 1(-1) lead in 2% v/v nitric acid) injected into a single-line. (3% v/v nitric acid) flow injection manifold, on 100 mg of Pb-Spec((R)) packed into a cylindrical column (6 cm X 4 mm internal diameter). The analytes, Ag, As, Bi, Cd, Cu, Sb and Sn, passed through the column and were quantified against matrix-matched standards. Only Ag showed significant retention, but could still be measured in an 8-min run. The column was rinsed by flushing with 0.1 M ammonium citrate solution. Lead was monitored by flame atomic absorption spectrometry in preliminary experiments concerning column capacity and breakthrough. Although the capacity of the material in the dynamic, flow-through mode was less than the literature value based on equilibrium studies, the lead from up to 13 successive injections was sufficiently retained to allow accurate determination of the analytes without intermediate rinsing of the column. The precision [percentage relative standard deviation (%R.S.D.), n = 5] of the procedure ranged from 1.7% (100 ng ml(-1) copper) to 2.8% (5 ng ml(-1) cadmium), and detection limits were in the range 0.2-10 ng ml(-1). The accuracy of the procedure was assessed by the analysis of three National Institute of Standards and Technology standard reference materials (SRM 2416 bullet lead, SRM 2415 battery lead, and SRM 2417 lead base alloy). For each SRM, duplicate determinations of seven analytes were made. Of the 42 determinations, 36 fell within the confidence interval around the accepted value. Three real bullets were analyzed for seven elements by both the flow injection solid-phase extraction ICP-MS method and by aspiration of the bullet solutions (10000 mg 1(-1) lead) directly into an ICP emission spectrometer. A linear least squares regression of these two sets of results gave aline with slope 1.01 +/- 0.04 and an intercept of -5 +/- 100 pg g(-1), where the terms are 95% confidence intervals. The column lifetime was in excess of 5 months of daily use, (C) 2001 Elsevier Science B.V. All rights reserved.