Precise lead isotope analysis using Multiple Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS): Analytical technique and evaluation of mass fractionation during Pb separation

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A precise Pb isotope analytical method using a double-focusing MC-ICP-MS routinely yields Pb isotope ratio sample data with an external reproducibility of ＜170ppm．This is achieved by making（a）an isobaric overlap correction of ^<204>Hg　on ^<204>Pb，（b）an external mass fractionation correction using ^<203>Tl/^<205>Tl，and（c）a mass-dependent mass fractionation conlection between Tl and Pb using a sample-standard bracket method．We also report that Pb isotope ratios are fractionated during the single column-single bead anion exchange procedure described in a previous report in this series，particularly if single bead Pb purification is used．If a sufficiently large volume of elutant（in this case ＞1 ml 6 NM HCl）is collected in the first column separation，there is no measurable fractionation of Pb isotopes．Single step Pb separation is suffcient for MC-ICP-MS，and consequently relatively rapid sample throughput is achievable，in combination with the rapid measurement possible with MC-ICP-MS（15 samples a day）．