Lead isotope ratio measurements in geological glasses by laser ablation-sector field-ICP mass spectrometry (LA-SF-ICPMS)

We have tested the capabilities of LA-SF-ICPMS for in situ Pb isotopic work on geological glasses using a 213 nm Nd:YAG laser system and a double focusing magnetic sector field ICP mass spectrometer. Experiments were done with the MPI-DING and USGS reference glasses, USGS rock powders molten as glass beads and basaltic glasses from Hawaii. In particular, the precision and accuracy of 208Pb/206Pb and 207Pb/206Pb ratios were investigated for three-spot analyses of glasses with different Pb contents (0.4-40 [mu]g/g) at spot sizes of 12-160 [mu]m. Using the fast and precise electrical scan mode, we obtained for samples with Pb concentration >1 [mu]g/g in-run precisions (1 R.S.E.) of better than 0.1% and 0.2% for spot diameters of 120 and 40 [mu]m, respectively. The LA-SF-ICPMS isotope ratios agree with the high-precision TIMS and MC-ICPMS data within the external precision (R.S.D. = 0.1-0.2%). The LA-SF-ICPMS results for 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb are less precise (about 0.5-1%) due to the low abundance of 204Pb and correction from the 204Hg interference. In this paper, we present the first LA-SF-ICPMS Pb isotope data for the MPI-DING (KL2-G, ATHO-G) and USGS reference glasses (BCR-2G, BHVO-2G) which may be useful for microanalytical in situ Pb isotope analysis. The findings of small (<2%), but significant differences in Pb isotope ratios of Hawaiian glasses of different ages, demonstrate that LA-SF-ICPMS is a suitable tool for geochemical research.