MPI-DING glasses: New geological reference materials for in situ Pb isotope analysis

Abstract

Advances in microanalytical techniques continue to revolutionize trace element and isotope geochemistry. Yet the lack of widely available geological reference materials has made interlaboratory comparisons and assessment of analytical accuracy difficult or impossible in many cases. The preparation and extensive analysis of the MPI-DING glasses has been designed to fill this gap. Here we report high-precision Pb isotope analyses by TIMS and MC-ICPMS techniques on seven geological MPI-DING glasses. The Pb concentrations in the reference glasses vary between 0.4 and 20 μg/g, allowing use in a wide range of analytical situations. In addition, solution ICPMS and LA-ICPMS analyses were used to investigate the analytical performance of a rapidly scanning single-collector sector-field mass spectrometer for the measurement of Pb isotope ratios. Our TIMS and MC-ICPMS measurements demonstrate that variations of 208Pb/206Pb and 207Pb/206Pb in most MPI-DING glasses are less than 0.03%. Preliminary reference values for 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb, 208Pb/206Pb, and 207Pb/206Pb were obtained by averaging all high-precision data and normalizing them to the mean triple spike data for NIST SRM 981, obtained in the Mainz laboratory. 208Pb/206Pb and 207Pb/206Pb ratios, which are commonly utilized for in situ Pb isotope studies, vary from 2.0110 (GOR132-G) to 2.0810 (T1-G) and 0.81656 (GOR132-G) to 0.84389 (GOR128-G), respectively. Any heterogeneity present in the glasses is generally lower than the reproducibility obtained from in situ microanalytical techniques, such as LA-ICPMS and SIMS (about 0.1–0.3% for 208Pb/206Pb and 207Pb/206Pb measurements). This is demonstrated by the results for our LA-ICPMS Pb isotope analyses using a single-collector sector-field ICP mass spectrometer, which agree to within 0.2% of the reference values. A similar accuracy was obtained from solution ICPMS using the same single-collector mass spectrometer.