In situ Mg isotope analysis of geological materials by laser ablation multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tracer technique for tracking geological processes. In the Mg...

In this study, we measure the absolute isotope ratios of ytterbium (Yb) by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using an optimized regression model for mass bias correction. A rhenium (Re) reference material (NIST SRM 3143), which has been characterized previously, is selected as a primary calibrator to calibrate the absolute Yb isotope ratios for three Yb materials (GSB, Alfa Yb, and GBW). The three-isotope plot for all collected data indicates that the results of Yb isotope ratios obtained are not affected by any polyatomic interferences and the mass-independent isotopic fractionation. Furthermore, the recalibrated Hf historical isotope ratios by using the absolute Yb isotopic composition obtained in this study for the isobaric interference correction on Hf isotopes are in agreement with the original historical values. This work has further demonstrated the applicability of the regression model for the calibrated measurements of absolute isotope ratios using MC-ICP-MS. The three mono-elemental Yb standard solutions are thus proposed as the reference materials for Yb isotope ratio measurements in environmental and geoscience applications.

The isotopic composition of lithium (Li) in clinopyroxene (Cpx), determined via in situ micro‐analysis, has been employed as a potential geochemical tool for studying various geological processes such as crust‐mantle recycling, silicate weathering and fluid‐rock interaction. To obtain precise and accurate Li isotopic compositions in Cpx by LA‐MC‐ICP‐MS, synthetic Cpx matrix‐matched reference materials (RMs) were prepared in this study. Six Cpx‐matrix RMs were prepared by mixing metallic oxides with GSP‐2 (granodiorite) or pure L‐SVEC solution and melting them into glasses (GSP‐2 + oxide; L‐SVEC + oxide). Two representative synthetic glasses, CPXA01 and CPXB01, were subjected to a series of analyses to investigate the possible qualification of the RMs for in situ Li isotope measurement by LA‐MC‐ICP‐MS, including elemental homogeneity analysis (elemental mapping analysis and spot analysis), Li isotopic homogeneity analysis and accurate Li isotopic determination. The applicability of the synthetic Cpx‐matrix RMs was highlighted by comparing the δ7Li values of three natural Cpx calibrated against the synthetic Cpx‐matrix RMs and other commonly used RMs with different matrices (NIST SRM 612, BCR‐2G, GOR128‐G, StHs6/80‐G, KL2‐G and T1‐G), respectively. Additionally, CPXB01‐05 RMs with the same matrix but different Li contents were prepared to explore the Li content mismatch effect, which is significant for accurate determination of in situ Li isotopic composition by LA‐MC‐ICP‐MS. The results of the cross‐calibration of Li isotopes in CPXA01 and CPXB01 suggested no obvious Li isotopic fractionation between the two types of glasses (GSP‐2 + oxide; L‐SVEC + oxide). Thus, the two methods of producing Cpx‐matrix RMs are suitable for preparing the matrix‐matched RMs for in situ microanalysis for Li isotopes.

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