Factorial optimization of data acquisition factors for lead isotope ratio determination by inductively coupled plasma mass spectrometry

A factorial optimization of data acquisition factors was performed to minimize non-random instrumental noise on an inductively coupled plasma mass spectrometer. Results have identified instrumental and analytical operating conditions under which lead isotope ratios can be measured precisely and accurately in natural samples. Precision was checked periodically over weeks and ranged 0.10-0.30, 0.15-0.35, 0.15-0.35, 0.10-0.30 and 0.10-0.20 (%) for 206/204, 207/204, 208/204, 206/207 and 208/206 ratios respectively. Mass bias was minimized and the correction factors were typically of 0.6% for 206/204, 1.5% for 207/204, 1.8% for 208/204, 0.8% for 206/207 and 1.2% for 208/206. These results were performed with a dwell time of 20 ms, 40 sweeps per replicate, 8 replicates by analysis, a time factor of 15 applied on mass 204 and three points per peak in the low resolution mode. The total duration time of an analysis was 10:50 min and it was found that optimum concentration of lead in solution was 50 ng ml(-1) on our instrument. (C) 1997 Elsevier Science B.V.