The determination of isotope ratios of lead finds many important applications in earth and planetary sciences. In this study, we report the first independent and fully calibrated absolute isotope ratio measurements of a common lead since the seminal work by the NIST in the 1960s, which has provided the widely used standards SRM 981 and SRM 982. This work employs MC-ICPMS for the absolute isotope ratio measurements, which were calibrated using two independent methods: the full gravimetric isotope mixture method based on the use of all four near-pure lead isotopes (the first application of this primary method to lead) and the regression method with NIST SRM 997 thallium isotopic standard as the primary calibrator. Both calibration methods provide results consistent to a few parts in 10 4 , which were used to characterize isotope ratios of lead in an NRC candidate reference material, high-purity common lead HIPB-1.

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A continuous-flow microwave-assisted digestion technique was tested with a view to the evaluation of its effectiveness for decomposition of environmental samples. A CEM SpectroPrep system was used at moderate powers and pressures of up to 2413 kPa to perform on-line digestion of slurried samples of biological tissues (0.5% m/v) and marine sediment (1% m/v). The efficiency of oxidation of biological matrices, as characterized by the residual carbon content of the solutions, was 64%. Recovery of trace elements averaged 90 f 1% and was accommodated with the use of suitable internal standards. Accuracy was verified by analysis of certified reference materials from the National Research Council of Canada, marine sediment BCSS-1 and lobster hepatopancreas tissue LUTS-1. Precision of measurement, as reflected in the determination of the trace metal content in replicate solutions, using a variety of atomic spectrometric techniques, was better than 1% RSD (relative standard deviation).

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