Isotope ratio analysis of lead in biological materials by inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) allowed 0.2-0.3% imprecision (1 sigma) in Pb-204/Pb-206, Pb-207/Pb-206, and Pb-208/Pb-206 measurements at the 20-100 ppb level, which was precise enough to detect some of the isotopic variations observed in nature. Mass discrimination could be corrected within +/-0.5% of the true value by periodical analysis of standard reference material of known lead isotopic composition. As a separation method for lead in human bone, which contains enormous amounts of calcium and phosphorus, anion exchange of the Pb-Br complex was found to be effective. Lead isotope ratios in bone, measured by ICP-MS after separation, were consistent with those measured by thermal ionization mass spectrometry. Hair matrix did not have any influence on the accuracy and precision of the analysis; a digested sample could be directly analyzed and this offered rapid sample throughput. Preliminary data on lead isotope ratios in bone and hair from prehistoric and contemporary Japanese are presented.