Evaluation of lead isotope compositions of NIST NBS 981 measured by thermal ionization mass spectrometer and multiple-collector inductively coupled plasma mass spectrometer

Because Pb isotopes can be used for tracing, they are widely used in many disciplines. The detection and analysis of Pb isotopes of bulk samples are usually conducted using thermal ionization mass spectrometer (TIMS) and multiple-collector inductively coupled plasma mass spectrometer (MC-ICP-MS), both of which need external reference materials with known isotopic compositions to correct for the mass discrimination effect produced during analysis. NIST NBS 981 is the most widely used reference material for Pb isotope analysis; however, the isotopic compositions reported by various analytical laboratories, especially those using TIMS, vary from each other. In this study, we statistically evaluated 229 reported TIMS analysis values collected by GeoReM in the last 30 years, 176 reported MC-ICP-MS analysis values, and 938 MC-ICP-MS analysis results from our laboratory in the last five years. After careful investigation, only 40 TIMS results were found to have double or triple spikes. The ratios of the overall weighted averages, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, obtained from 40 spiked TIMS reports and 1114 MC-ICP-MS results of NIST NBS 981 isotopes were 16.9406 ± 0.0003 (2s), 15.4957 ± 0.0002 (2s), and 36.7184 ± 0.0007 (2s), respectively.