ROUTINE LEAD-ISOTOPE DETERMINATIONS USING A PB-207 PB-204 DOUBLE SPIKE - A LONG-TERM ASSESSMENT OF ANALYTICAL PRECISION AND ACCURACY

Lead-isotope data obtained on a multicollector mass spectrometer over a four year period using a Pb-207-Pb-204 double spike to correct for t he effects of mass discrimination, are reported. Considerable improvem ents in both precision end accuracy over conventional correction proce dures were noted, without recourse to rigorous loading or run conditio ns. An external precision in Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/P b-204 ratios +/-0.003, 0.003 and 0.01 (2 x standard deviation), respec tively, is routinely obtainable independent of minor variations in loa ding and run parameters.