Simultaneous Determination of Trace Elements and Lead Isotopes in Fused Silicate Rock Powders Using a Boron Nitride Vessel and fsLA-(MC)-ICP-MS

Abstract

A new glass-making method was developed to allow the in situ analysis of trace elements and lead isotopes in rock samples. The apparatus used to prepare homogeneous glass samples from silicate rock powder consisted of a small (450 mm³) boron nitride vessel and a high-temperature furnace. The concentrations of trace elements were measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and lead isotopic compositions were measured by femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). The method was evaluated by analyzing glass disks fused from six geochemical reference materials (spanning the compositional range basalt–andesite–rhyolite). The measured 34 trace element contents match the reference values within 15%, and the mean Pb isotopic ratios measured by fsLA-MC-ICP-MS agree with those obtained by solution nebulizer MC-ICP-MS within 2s uncertainty intervals. By using seven Faraday cups operating in static mode we were able to obtain ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb results with improved precisions by a factor of 2–3 compared to those obtained by previous single-collector sector-field ICPMS and LA-MC-ICP-MS. The accuracies of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb values obtained by fsLA-MC-ICP-MS lie between −0.073% and +0.023%, which are well determined for geological research. Measured ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb isotope ratios for the USGS reference RGM-2 (20 μg g⁻¹ total Pb) and BCR-2 (11 μg g⁻¹ total Pb) agree within 0.029% and 0.055% respectively of the preferred values. For GSR-3 (4.27 μg g⁻¹ total Pb), the accuracies of the ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb ratios obtained by fsLA-MC-ICP-MS lie between −0.064% and −0.004% with the accepted external precision of <0.15% (1RSD), which are better than previous LA-MC-ICP-MS data in terms of quantification limits. We also provide precise Pb isotopic data for the reference materials GSR-2, GSR-3, QLO-1, and RGM-2 obtained by solution nebulizer MC-ICP-MS. Our method is simpler, cheaper and faster to determine trace elements and Pb isotopic ratios in geological samples, while retaining similar levels of accuracy and precision.