Precise determination of Pb isotope ratios by simple double spike MC-ICP-MS technique without Tl addition

Abstract

A double-spike multicollector ICP-MS (DS-MC-ICP-MS) technique for Pb isotope analysis without Tl addition is established and its analytical performance is examined in detail. This simple DS-MC-ICP-MS technique using 20 ng ml⁻¹ gave averages of 16.9417, 15.4988 and 36.7196 with reproducibilities of 0.007, 0.008 and 0.009% (RSD, n = 35), respectively, for ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb in NIST 981 solution, corresponding to consumption of 4 ng of Pb in a pair of spiked and non-spiked measurements. The average is consistent with those obtained by previous studies by DS-TIMS and DS-MC-ICP-MS with Tl addition. The reproducibility (RSD %) of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb improves from 0.26, 0.54 and 0.69% to 0.0022, 0.0030 and 0.0029% as the Pb consumption during analysis increases from 20 pg to 11 ng. The reproducibility with 11 ng is similar to or even better than those by DS-TIMS, MC-ICP-MS with Tl addition, or with DS-Tl addition. The accuracy of the simple DS-MC-ICP-MS technique for Pb, including the column chemistry, is further confirmed by analysis of actual silicate sample, JB-3.