VERIFICATION OF A CORRECTION PROCEDURE FOR MEASUREMENT OF LEAD ISOTOPE RATIOS BY INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

Inductively coupled plasma mass spectrometry (ICP-MS) is a suitable method for determining Pb isotope ratios. This study investigates the effectiveness of a mass discrimination correction technique, which is based upon the addition of Tl to the sample and measurement of the Tl-205:Tl-203 ratio. The Tl correction method has been found to be highly effective for minimizing bias and drift in Pb isotope ratios under a variety of operating and sample matrix conditions, and for various samples independently analysed by thermal ionization mass spectrometry (TIMS). Biases for ratios with respect to Pb-204 are generally controlled at < 0.5% and relative standard deviations of 0.2% are attainable. Results using ICP-MS for environmental samples compare favourably with those obtained by TIMS. This correction technique is suitable for routine analysis of environmental samples.