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Rationale: The boron (B) isotopic composition in marine carbonates provides important insights into paleoclimate reconstruction and biomineralization. However, precise and accurate measurements of B isotopes using plasma-based mass spectrometry is difficult due to the volatile nature of B, which typically requires complex and more specialized sample introduction systems. Existing analytical protocols have mostly been based on Thermo Scientific Neptune Plus multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) instruments, whereas methods based on Nu Plasma mass spectrometers are scarce., Methods: We have developed a simplified analytical protocol using Nu Plasma II MC-ICPMS with standard glass sample introduction systems. Boron extraction and purification were conducted using a two-stage column chemistry with cation-exchange and Amberlite IRA 743 B-specific resin. A sample drying step was avoided, which allows for direct isotopic analysis after column chemistry. A wet plasma mode with a standard glass cyclonic spray chamber and a glass nebulizer was used instead of a more specialized perfluoroalkoxy (PFA) sample introduction system. Low residual B signals were achieved with a relatively short period of wash-out with 0.5 N HNO 3 ., Results: The external precision is better than 0.30‰ (2SD) calculated from the long-term bracketing standard, NIST SRM 951a. The overall robustness of the method was demonstrated by measurements of the international carbonate standard JCp-1 (δ 11 B = +24.49 ± 0.36‰, 2SD) and seawater (δ 11 B = +39.98 ± 0.35‰), which are consistent with reported values., Conclusions: Our method provides an alternative approach for B isotope analysis using a routine wet plasma MC-ICPMS setup that can facilitate geochemical and environmental application of B isotopes., (© 2019 John Wiley & Sons, Ltd.)

Rationale: Previous analyses on San Carlos olivine from Arizona (USA) have shown inter-laboratory δ(26) Mg differences of up to 0.67‰, while mantle olivine samples worldwide are homogeneous at a current analytical uncertainty of ~0.1‰. The differing measurements on San Carlos olivine may be attributable to analytical artifacts or sample heterogeneity. The latter must be ruled out before using it as a standard for Mg isotopic analysis., Methods: To examine sample homogeneity, two different batches of San Carlos olivine from a lherzolite and four batches from a harzburgite have been analyzed together with coexisting harzburgitic pyroxene. In addition, the effect of acid purity on resin performance and the reusability of AG50W-X8 resin for Mg separation have been evaluated by processing another batch of lherzolitic San Carlos olivine and Hawaiian seawater through both new and used resins cleaned with different acids., Results: Six different batches of olivine grains from two San Carlos peridotite xenoliths show homogeneous δ(26) Mg values to within 0.03‰, and all the mineral phases in the harzburgite are in Mg isotope equilibrium. Furthermore, there is no resolvable δ(26) Mg shift in either lherzolitic San Carlos olivine or Hawaiian seawater by using either new or used resins that were cleaned with single-distilled or double-distilled acids., Conclusions: The new data are consistent with the narrow δ(26) Mg range of mantle olivine worldwide, while they stand in contrast to the wide range measured on the same San Carlos olivine powder in different laboratories. Therefore, previous inter-laboratory discrepancies reflect analytical artifacts instead of sample heterogeneity, and San Carlos olivine is a suitable standard for Mg isotopic analysis. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)

Rationale: High accuracy is the prerequisite for high-precision isotopic analysis., Methods: Here we evaluate how the presence of matrix elements, and mismatch between samples and standards in Mg concentration and acid molarity affect the accuracy of stable Mg isotopic analysis on Nu Plasma and IsoProbe multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) instruments., Results: Our results show that these factors can lead to large (>1‰) deviation in the high-precision analysis of Mg isotopes. The degree and direction of these accuracy offsets can vary for different instruments, instrumental settings and different laboratories., Conclusions: Detailed tests and tight controls on these effects are thus needed for high-precision high-accuracy stable Mg isotopic analysis., (Copyright © 2013 John Wiley & Sons, Ltd.)

The magnesium (Mg) isotopic compositions of 40 seawater samples from the Gulf of Mexico and of one seawater sample from the southwest Hawaii area were determined by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) to investigate the homogeneity of Mg isotopes in seawater. The results indicate that the Mg isotopic composition of seawater from the Gulf of Mexico is homogeneous, both vertically and horizontally, with average values for δ(26)Mg = -0.832 ± 0.068 and δ(25)Mg = -0.432 ± 0.053 (n = 40, 2SD)--identical to those of seawater from Hawaii (average δ(26)Mg = -0.829 ± 0.037 and δ(25)Mg = -0.427 ± 0.033) and to the average literature values of seawater worldwide (δ(26)Mg = -0.83 ± 0.11 and δ(25)Mg = -0.43 ± 0.06, n = 49, 2SD). Collectively, global seawater has a homogeneous Mg isotopic composition with δ(26)Mg = -0.83 ± 0.09 and δ(25) Mg = -0.43 ± 0.06 (2SD, n = 90). The magnesium isotopic composition of seawater is principally controlled by river water input, carbonate precipitation and oceanic hydrothermal interactions. The homogeneous Mg isotopic composition of seawater indicates a steady-state budget in terms of Mg isotopes in oceans, consistent with a long Mg residence time (~13 Ma). Considering that seawater is homogeneous, readily available in large amounts, can be easily accessed and processed for isotopic analysis, and has an isotopic composition near the middle of the natural range of variation, it is an excellent geostandard for accuracy assessment to rule out analytical artifacts during high-precision Mg isotopic analysis., (Copyright © 2011 John Wiley & Sons, Ltd.)