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 plasm a mass spectrometer. Results have identified instrumental and analytic al operating conditions under which lead isotope ratios can be measure d precisely and accurately in natural samples. Precision was checked p eriodically over weeks and ranged 0.10-0.30, 0.15-0.35, 0.15-0.35, 0.1 0-0.30 and 0.10-0.20 (%) for 206/204, 207/204, 208/204, 206/207 and 20 8/206 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 pe rformed with a dwell time of 20 ms, 40 sweeps per replicate, 8 replica tes by analysis, a time factor of 15 applied on mass 204 and three poi nts 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 Elsevie r Science B.V.