Intercomparison of Boron Isotope and Concentration Measurements. Part II: Evaluation of Results

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ¹¹B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution.     

Boron Isotopic Composition and Concentration of Ten Geological Reference Materials

We present boron isotope and concentration data from magmatic (komatiitic to rhyolitic) and sedimentary geological silicate and artificial glass reference materials that cover a wide spectrum of boron isotope compositions and boron concentrations. Boron isotope compositions were determined by TIMS (Cs₂BO₂⁺ -graphite and BO₂^- method) and boron concentrations by ICP-AES. Boron concentrations ranged from 7 to 159μ g^-1 and agree within 14% with published values. Based on replicate analyses of individually prepared sample aliquots an overall external reproducibility of better than 10% was determined. The obtained δ¹¹B values ranged from -12.6 to +13.6% and were reproducible within 1.1 % (2 RSD; excluding NTIMS) on the basis of individually prepared sample aliquots. The δ¹¹B values of JA-1 (+5.3%), JB-3 (+5.9%) and JR-2 (+2.9%) overlap the published data within analytical uncertainty. For the first time δ¹¹B values for the TB (-12.6%) and the MPI-DING glasses GOR-128-G (+13.6%), GOR-132-G (+7.1 %) and StHs6/80-G (-4.5%) are reported. The δ¹¹B values obtained by the Cs₂BO₂⁺ -graphite and the BO₂^- method as well as the majority of δ¹¹B values obtained using different sample preparation methods agree within analytical uncertainty. Therefore, we conclude that none of these analytical methods introduce any systematic error on the obtained δ¹¹B values.     

Composition-Induced Variations in SIMS Instrumental Mass Fractionation during Boron Isotope Ratio Measurements of Silicate Glasses

An analytical artefact is reported here related to differences in instrumental mass fractionation between NIST SRM glasses and natural geological glasses during SIMS boron isotope determinations. The data presented demonstrated an average 3.4‰ difference between the NIST glasses and natural basaltic to rhyolitic glasses mainly in terms of their sputtering-induced fractionation of boron isotopes. As no matrix effect was found among basaltic to rhyolitic glasses, instrumental mass fractionation of most natural glass samples can be corrected by using appropriate glass reference materials. In order to confirm the existence of the compositionally induced variations in boron SIMS instrumental mass bias, the observed offset in SIMS instrumental mass bias has been independently reproduced in two laboratories and the phenomenon has been found to be stable over a period of more than one year. This study highlights the need for a close match between the chemical composition of the reference material and the samples being investigated.     

Basaltic and Solution Reference Materials for Iron,Copper and Zinc Isotope Measurements

Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS‐Fe, CAGS‐Cu and CAGS‐Zn) and one basalt (CAGS‐Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter‐laboratory analytical comparisons involving up to eight participating laboratories employing MC‐ICP‐MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM‐014 for Fe, NIST SRM 976 for Cu and IRMM‐3702 for Zn. Respective reference values of CAGS‐Fe, CAGS‐Cu and CAGS‐Zn solutions are as follows: δ⁵⁶Fe = 0.83 ± 0.07 and δ⁵⁷Fe = 1.20 ± 0.13, δ⁶⁵Cu = 0.57 ± 0.06, and δ⁶⁶Zn = ?0.79 ± 0.12 and δ⁶⁸Zn = ?1.65 ± 0.24, respectively. Those of CAGS‐Basalt are δ⁵⁶Fe = 0.15 ± 0.07, δ⁵⁷Fe = 0.22 ± 0.10, δ⁶⁵Cu = 0.12 ± 0.08, δ⁶⁶Zn = 0.17 ± 0.13, and δ⁶⁸Zn = 0.34 ± 0.26 (2s).     

Lead Isotope Homogeneity of NIST SRM 610 and 612 Glass Reference Materials: Constraints from Laser Ablation Multicollector ICP-MS (LA-MC-ICP-MS) Analysis

This contribution presents data for laser ablation multicollector ICP‐MS (LA‐MC‐ICP‐MS) analyses of NIST SRM 610 and 612 glasses with the express purpose of examining the Pb isotope homogeneity of these glasses at the ～ 100 μm spatial scale, relevant to in situ analysis. Investigation of homogeneity at these scales is important as these glasses are widely used as calibrators for in situ measurements of Pb isotope composition. Results showed that at the levels of analytical uncertainty obtained, there was no discernable heterogeneity in Pb isotope composition of NIST SRM 610 and also most probably for NIST SRM 612. Traverses across the ～ 1.5 mm glass wafers supplied by NIST, consisting of between 75 and 133 individual measurements, showed no compositional outliers at the two standard deviation level beyond those expected from population statistics. Overall, the measured Pb isotope ratios from individual traverses across NIST SRM 610 and 612 wafers closely approximate single normally‐distributed populations, with standard deviations similar to the average internal uncertainty for individual measurement blocks. Further, Pb isotope ratios do not correlate with Tl/Pb ratios measured during the analysis, suggesting that regions of volatile element depletion (marked by low Tl/Pb) in these glasses are not associated with changes in Pb isotope composition. For NIST SRM 610 there also appeared to be no variation in Pb isotope composition related to incomplete mixing of glass base and trace element spike during manufacture. For NIST SRM 612 there was some dispersion of measured ratios, including some in a direction parallel to the expected mixing line for base‐spike mixing. However, there was no significant correlation parallel to the mixing line. At this time this cannot be unequivocally demonstrated to result from glass heterogeneity, but it is suggested that NIST SRM 610 be preferred for standardising in situ Pb isotope measurements. Data from this study also showed significantly better accuracy and somewhat better precision for ratios corrected for mass bias by external normalisation to Pb isotope ratios measured in bracketing calibrators compared to mass bias corrected via internal normalisation to measured ²⁰⁵Tl/²⁰³Tl, although the Tl isotopic composition of both glasses appears to be homogeneous.     

New Reference Materials,Analytical Procedures and Data Reduction Strategies for Sr Isotope Measurements in Geological Materials by LA-MC-ICP-MS

Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peak-stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE²⁺ correction for rock glasses, yields the most accurate and precise ⁸⁷Sr/⁸⁶Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for ⁸⁷Sr/⁸⁶Sr measurements for materials with < 1000 μg g^-1 Sr.     

岩石铷-锶和钐-钕同位素标准物质的研制

通常样品的87Sr/86Sr和143Nd/144Nd同位素比值分析采用SRM987、JNdi-1作为标准物质,它们分别是纯的碳酸盐和氧化物,适用于监控质谱测试过程。中国现有的钐-钕地质和铷-锶年龄标准物质,分别为玄武岩和钾长石,它们与很多地质样品的基质存在差别。仅有这两种基质的标准物质不能有效地监控不同地质样品Rb-Sr、Sm-Nd同位素分析过程,因此研制不同岩性的Rb-Sr、Sm-Nd同位素标准物质具有重要现实意义。本文采集中国典型地区的橄榄岩、榴辉岩和花岗岩作为候选物,严格按照《一级标准物质技术规范》（JJF 1006—1994）和《标准物质定值的通用原则及统计学原理》（JJF 1343—2012）等相关标准物质国家计量技术规范和国家标准,研制了橄榄岩、榴辉岩和花岗岩铷-锶、钐-钕同位素标准物质（编号为GBW04139、GBW04140、GBW04141）,其中橄榄岩标准物质适用于高Mg、Fe,低Rb、Nd含量样品的分析,榴辉岩和花岗岩标准物质适用于含有难溶副矿物的岩石样品的分析。每个标准物质具有6个特性量值,Rb、Sr、Sm和Nd含量分布分别为0.16~64μg/g、12~560μg/g、0.1~3.2μg/g和0.3~15.3μg/g,87Sr/86Sr比值分布为0.70446~0.71309,143Nd/144Nd比值分布为0.51115~0.51267,同位素比值精度达到或优于同类标准物质。这些特性量值更接近实际样品,使用时将更加有效和方便。该系列标准物质可用于校准仪器和评价方法,并能有效监控实验室此类样品的铷-锶、钐-钕同位素分析过程。     

Three Secondary Reference Materials for Lithium Isotope Measurements: Li7-N, Li6-N and LiCl-N Solutions

The CRPG (Nancy, France) has prepared secondary reference materials for Li isotope measurements by mixing ⁷Li or ⁶Li spikes and either L-SVEC or IRMM-016 certified reference materials to produce solutions having a known Li concentration and isotopic composition. The Li7-N and Li6-N solution samples (1.5 mol l⁻¹ HNO₃) have nominal δ⁷Li isotopic compositions of 30.1‰ and -9.7‰ respectively relative to L-SVEC and concentrations of 100 mg l⁻¹. Repeated measurement of these samples using the QUAD-ICP-MS at the CRPG yielded δ⁷Li of 30.4 ± 1.1‰ (n = 13) and -8.9 ± 0.9‰ (n = 9) at the 2s level of confidence. An additional LiCl-N solution was measured and yielded a delta value of 9.5 ± 0.6‰ (n = 3). Identical results were obtained at the BRGM (Orléans, France) from determinations performed with a Neptune MC-ICP-MS (30.2 ± 0.3‰, n = 89 for the Li7-N, -8.0 ± 0.3‰, n = 38 for the Li6-N and 10.1 ± 0.2‰, n = 46 for LiCl-N at the 2s level of confidence). The deviation of measured composition relative to the nominal value for the Li6-N solution might be explained by either contamination during preparation or an error during sample weighing. These secondary reference materials, previously passed through ion exchange resin or directly analysed, may be used for checking the accuracy of Li isotopic measurements over a range of almost 40‰ and will be available to the scientific community upon request to J. Carignan or N. Vigier, CRPG.     

Characterisation of Three Sri Lankan Zircon Megacrysts as Potential Reference Materials for Microbeam U-Pb Geochronology and Hf-O-Zr Isotope Measurements

In situ U-Pb geochronology and hafnium, oxygen and zirconium isotope measurements in zircons using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and ion microprobe techniques can provide essential isotopic data to constrain geological evolutionary histories. Developing reliable zircon reference materials is the cornerstone for in situ zircon chronology and isotopic studies. In this study, the homogeneity of U-Pb ages and Hf-O-Zr isotope ratios in three Sri Lankan zircon megacrysts (SLZA, SLZB and SLZC) were investigated using multiple analytical methods. The obtained U, Th, Pb and Hf mass fractions of the SLZA zircon were 839 ± 56 μg g^-1 (1s), 151 ± 15 μg g^-1 (1s), 198 ± 28 μg g^-1 (1s) and 8635 ± 286 μg g^-1 (1s), respectively. The mass fractions of U, Th, Pb and Hf in the SLZB zircon were 1106 ± 106 μg g^-1 (1s), 331 ± 61 μg g^-1 (1s), 376 ± 57 μg g^-1 (1s) and 9673 ± 976 μg g^-1 (1s), respectively. The U, Th, Pb and Hf mass fractions determined in the SLZC zircon were 551 ± 35 μg g^-1 (1s), 111 ± 8 μg g^-1 (1s), 129 ± 18 μg g^-1 (1s) and 7881 ± 393 μg g^-1 (1s), respectively. The chemical abrasion isotope dilution thermal ionisation mass-spectrometry (CA-ID-TIMS) method yielded a Th-corrected weighted mean ²⁰⁶Pb/²³⁸U age of 556.94 ± 1.29 Ma (95% conf., n = 5) for the SLZA zircon, 552.90 ± 1.29 Ma (95% conf., n = 7) for the SLZB zircon and 560.83 ± 1.29 Ma (95% conf., n = 7) for the SLZC zircon. The obtained Hf isotopic compositions of the SLZA, SLZB and SLZC zircons determined with the solution MC-ICP-MS method were 0.281651 ± 0.000014 (2s, n = 10), 0.281704 ± 0.000008 (2s, n = 10) and 0.281676 ± 0.000006 (2s, n = 10), respectively. The obtained O isotopes of the SLZA and SLZB zircons measured with the laser fluorination method were 12.14 ± 0.56‰ (2s, n = 4) and 11.91 ± 0.30‰ (2s, n = 4), respectively. The Zr isotopes of the SLZA, SLZB and SLZC zircons determined with double spike TIMS analysis yielded mean δ⁹⁴/⁹⁰Zr_SRM3169 values of -0.03 ± 0.06‰ (2s, n = 10), -0.03 ± 0.04‰ (2s, n = 10) and 0.00 ± 0.07‰ (2s, n = 8), respectively. The SLZA zircon can be used as a primary reference or quality control material for microbeam U-Pb, Hf and Zr isotope measurements because of its slight heterogeneity. The U-Pb, Hf and Zr isotopic compositions of the SLZB and SLZC megacrysts were homogeneous. The O isotopic compositions in the SLZA and SLZB zircon were slightly dispersed, indicating that these two megacrysts can only serve as secondary reference materials for microbeam O isotope measurements.     

Production and Certification of a Unique Set of Isotope and Delta Reference Materials for Boron Isotope Determination in Geochemical,Environmental and Industrial Materials

Isotopic reference materials are essential to enable reliable and comparable isotope data. In the case of boron only a very limited number of such materials is available, thus preventing adequate quality control of measurement results and validation of analytical procedures. To address this situation a unique set of two boron isotope reference materials (ERM‐AE102a and ‐AE104a) and three offset δ¹¹B reference materials (ERM‐AE120, ‐AE121 and ‐AE122) were produced and certified. The present article describes the production and certification procedure in detail. The isotopic composition of all the materials was adjusted by mixing boron parent solutions enriched in ¹⁰B or ¹¹B with a boron parent solution having a natural isotopic composition under full gravimetric control. All parent solutions were analysed for their boron concentration as well as their boron isotopic composition by thermal ionisation mass spectrometry (TIMS) using isotope dilution as the calibration technique. For all five reference materials the isotopic composition obtained on the basis of the gravimetric data agreed very well with the isotopic composition obtained from different TIMS techniques. Stability and homogeneity studies that were performed showed no significant influence on the isotopic composition or on the related uncertainties. The three reference materials ERM‐AE120, ERM‐AE121 and ERM‐AE122 are the first reference materials with natural δ¹¹B values not equal to 0‰. The certified δ¹¹B values are ?20.2‰ for ERM‐AE120, 19.9‰ for ERM‐AE121 and 39.7‰ for ERM‐AE122, each with an expanded uncertainty (k = 2) of 0.6‰. These materials were produced to cover about three‐quarters of the known natural boron isotope variation. The ¹⁰B enriched isotope reference materials ERM‐AE102a and ERM‐AE104a were produced for industrial applications utilising ¹⁰B for neutron shielding purposes. The certified ¹⁰B isotope abundances are 0.29995 for ERM‐AE102a and 0.31488 for ERM‐AE104a with expanded uncertainties (k = 2) of 0.00027 and 0.00028, respectively. Together with the formerly certified ERM‐AE101 and ERM‐AE103 a unique set of four isotope reference materials and three offset δ¹¹B reference materials for boron isotope determination are now available from European Reference Materials.     

Potential Orthopyroxene,Clinopyroxene and Olivine Reference Materials for In Situ Lithium Isotope Determination

Over 1400 electron probe and 700 ion probe microanalyses were performed on eleven mineral separates to evaluate their potential as reference materials for in situ Li isotopic determination. Our results suggest the homogenous distributions of major elements, Li and its isotopes for each sample. Hence, these samples are suitable to be used as reference materials for in situ measurements of Li abundance and Li isotopes by secondary ion mass spectrometry (SIMS) or laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). These samples have the advantage of mitigating probable matrix effects during calibration owing to the wide range of compositions. The effect of composition on the δ⁷Li of olivine measured by SIMS is a linear function of composition, with δ⁷Li increasing by 1.0‰ for each mole per cent decrease in forsterite component.     

CGSG系列标准物质元素分馏效应及主量微量元素单元内均匀性探究

探究CGSG系列标准物质(CGSG-1、CGSG-2、CGSG-4、CGSG-5)的元素分馏效应及均匀性问题有助于开展其质量评估和应用推广。本文采用电子探针(EMPA)和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)研究了CGSG标准物质中的元素分馏效应、主量和微量元素单元内均匀性,并报道了主量和微量元素分析数据。结果表明,在50μm激光束斑下,CGSG系列标准物质的元素分馏效应可忽略不计。EMPA均匀性指数结果显示,CGSG标准物质主量元素的单元内均匀性满足要求;以MPI-DING标准物质为参照,LA-ICP-MS测试CGSG标准物质中的大多数微量元素的单元内均匀性良好。与已报道的数据相比,本文报道的EMPA主量元素数据偏差在2%以内;LA-ICP-MS主量元素数据偏差在5%以内,微量元素数据基本匹配,少数元素由于分析不确定度较大等原因,如Cr、Ge、Cd、As、Tl等与已报道数据偏差较大。总体上,本文报道的分析数据可为CGSG定值数据库提供进一步的补充。     

Development of Synthetic Clinopyroxene Reference Materials for In Situ Lithium Isotope Measurement by LA-MC-ICP-MS

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.     

Tourmaline Reference Materials for the In Situ Analysis of Oxygen and Lithium Isotope Ratio Compositions

Three tourmaline reference materials sourced from the Harvard Mineralogical and Geological Museum (schorl 112566, dravite 108796 and elbaite 98144), which are already widely used for the calibration of in situ boron isotope measurements, are characterised here for their oxygen and lithium isotope compositions. Homogeneity tests by secondary ion mass spectrometry (SIMS) showed that at sub‐nanogram test portion masses, their ¹⁸O/¹⁶O and ⁷Li/⁶Li isotope ratios are constant within ± 0.27‰ and ± 2.2‰ (1s), respectively. The lithium mass fractions of the three materials vary over three orders of magnitude. SIMS homogeneity tests showed variations in ⁷Li/²⁸Si between 8% and 14% (1s), which provides a measure of the heterogeneity of the Li contents in these three materials. Here, we provide recommended values for δ¹⁸O, Δ’¹⁷O and δ⁷Li for the three Harvard tourmaline reference materials based on results from bulk mineral analyses from multiple, independent laboratories using laser‐ and stepwise fluorination gas mass spectrometry (for O), and solution multi‐collector inductively coupled plasma‐mass spectroscopy (for Li). These bulk data also allow us to assess the degree of inter‐laboratory bias that might be present in such data sets. This work also re‐evaluates the major element chemical composition of the materials by electron probe microanalysis and investigates these presence of a chemical matrix effect on SIMS instrumental mass fractionation with regard to δ¹⁸O determinations, which was found to be < 1.6‰ between these three materials. The final table presented here provides a summary of the isotope ratio values that we have determined for these three materials. Depending on their starting mass, either 128 or 512 splits have been produced of each material, assuring their availability for many years into the future.     

A Preliminary Appraisal of Seven Natural Zircon Reference Materials for In Situ Hf Isotope Determination

There is a growing need for new zircon reference materials for in situ Hf-isotope analysis by laser ablation-multicollector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS). In this contribution we document the results of a preliminary investigation of seven natural zircons, conducted in order to test their suitability in this regard. Solution MC-ICP-MS data on separated Lu and Hf fractions provided reference compositional data while the results of ca. 750 in situ LA-MC-ICP-MS analyses allowed assessment of potential micrometre-scale heterogeneity. On the basis of these analyses and additional relevant considerations such as availability, size and (Lu)Yb/Hf ratio, we suggest that, of the currently available zircons, Temora-2 and Mud Tank are most likely to provide robust reference materials for Hf isotope determinations both at the present time and into the future. The former has the advantage of also being well-characterised for U-Th-Pb systematics and suitable for in situ age determination, while the latter is the most readily available and is of very large grain size. Additional materials such as BR266, and 91500, although limited in supply, show more consistent Lu/Hf ratios and are thus of use in monitoring elemental fractionation during ICP-MS analysis.     

An Intercomparison Study of the Germanium Isotope Composition of Geological Reference Materials

Recent analytical developments in germanium stable isotope determination by multicollector ICP‐MS have provided new perspectives for the use of Ge isotopes as geochemical tracers. Here, we report the germanium isotope composition of the NIST SRM 3120a elemental reference solution that has been calibrated relative to internal isotopic standard solutions used in the previous studies. We also intercalibrate several geological reference materials as well as geological and meteoritic samples using different techniques, including online hydride generation and a spray chamber for sample introduction to MC‐ICP‐MS, and different approaches for mass bias corrections such as sample–calibrator bracketing, external mass bias correction using Ga isotopes and double‐spike normalisation. All methods yielded relatively similar precisions at around 0.1‰ (2s) for δ^74/70Ge values. Using igneous and mantle‐derived rocks, the bulk silicate Earth (BSE) δ^74/70Ge value was re‐evaluated to be 0.59 ± 0.18‰ (2s) relative to NIST SRM 3120a. Several sulfide samples were also analysed and yielded very negative values, down to ?4.3‰, consistent with recent theoretical study of Ge isotope fractionation. The strong heavy isotope depletion in ore deposits also contrasts with the generally positive Ge isotope values found in many modern and ancient marine sediments.     

Thallium Mass Fraction and Stable Isotope Ratios of Sixteen Geological Reference Materials

Thallium stable isotope ratio and mass fraction measurements were performed on sixteen geological reference materials spanning three orders of magnitude in thallium mass fraction, including both whole rock and partially separated mineral powders. For stable isotope ratio measurements, a minimum of three independent digestions of each reference material was obtained. High‐precision trace element measurements (including Tl) were also performed for the majority of these RMs. The range of Tl mass fractions represented is 10 ng g^?1 to 16 μg g^?1, and Tl stable isotope ratios (reported for historical reasons as ε²⁰⁵Tl relative to NIST SRM 997) span the range ?4 to +2. With the exception – attributed to between‐bottle heterogeneity – of G‐2, the majority of data are in good agreement with published or certified values, where available. The precision of mean of independent measurement results between independent dissolutions suggests that, for the majority of materials analysed, a minimum digested mass of 100 mg is recommended to mitigate the impact of small‐scale powder heterogeneity. Of the sixteen materials analysed, we therefore recommend for use as Tl reference materials the USGS materials BCR‐2, COQ‐1, GSP‐2 and STM‐1; CRPG materials AL‐I, AN‐G, FK‐N, ISH‐G, MDO‐G, Mica‐Fe, Mica‐Mg and UB‐N; NIST SRM 607 and OREAS14P.     

NIST RM 8301 Boron Isotopes in Marine Carbonate (Simulated Coral and Foraminifera Solutions): Inter‐laboratory δ11B and Trace Element Ratio Value Assignment

The boron isotopic ratio of ¹¹B/¹⁰B (δ¹¹B_SRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ¹¹B_SRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ¹¹B_SRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes.     

Boron and Oxygen Isotope Composition of Certified Reference Materials NIST SRM 610/612 and Reference Materials JB-2 and JR-2

We present data on the concentration, the isotope composition and the homogeneity of boron in NIST silicate glass reference materials SRM 610 and SRM 612, and in powders and glasses of geological reference materials JB-2 (basalt) and JR-2 (rhyolite). Our data are intended to serve as references for both microanalytical and wet-chemical techniques. The δ¹¹ B compositions determined by N-TIMS and P-TIMS agree within 0.5% and compare with SIMS data within 2.5%. SIMS profiles demonstrate boron isotope homogeneity to better than δ¹¹ B = 2% for both NIST glasses, however a slight boron depletion was detected towards the outermost 200 μm of the rim of each sample wafer. The boron isotope compositions of SRM 610 and SRM 612 were indistinguishable. Glasses produced in this study by fusing JB-2 and JR-2 powder also showed good boron isotope homogeneity, both within and between different glass fragments. Their major element abundance as well as boron isotope compositions and concentrations were identical to those of the starting composition. Hence, reference materials (glasses) for the in situ measurement of boron isotopes can be produced from already well-studied volcanic samples without significant isotope fractionation. Oxygen isotope ratios, both within and between wafers, of NIST reference glasses SRM 610 and SRM 612 are uniform. In contrast to boron, significant differences in oxygen isotope compositions were found between the two glasses, which may be due to the different amounts of trace element oxides added at ten-fold different concentration levels to the silicate matrix.     

Lithium Isotope Composition of Marine Biogenic Carbonates and Related Reference Materials

In this study, the accuracy and the precision corresponding to Li isotopic measurements of low level samples such as marine and coastal carbonates are estimated. To this end, a total of fifty‐four analyses of a Li‐pure reference material (Li7‐N) at concentrations ranging from 1 to 6 ng ml^?1 were first performed. The average δ⁷Li values obtained for solutions with and without chemical purification were 30.3 ± 0.4‰ (2s, n = 19) and 30.2 ± 0.4‰ (2s, n = 36), respectively. These results show that the chosen Li chemical extraction and purification procedure did not induce any significant isotope bias. Two available carbonate reference materials (JCt‐1 and JCp‐1) were analysed, yielding mean δ⁷Li values of 18.0 ± 0.27‰ (2s, n = 6) and 18.8 ± 1.8‰ (2s, n = 9), respectively. Small powder aliquots (< 15 mg) of JCp‐1 displayed significant isotope heterogeneity and we therefore advise favouring JCt‐1 for interlaboratory comparisons. The second part of this study concerns the determination of δ⁷Li value for biogenic carbonate samples. We performed a total of twenty‐nine analyses of seven different tropical coral species grown under controlled and similar conditions (24.0 ± 0.1 °C). Our sample treatment prior to Li extraction involved removal of organic matter before complete dissolution in diluted HCl. Our results show (a) a constant δ⁷Li within each skeleton and between the different species (δ⁷Li = 17.3 ± 0.7‰), and (b) a Li isotope fractionation of ?2‰ compared with inorganic aragonite grown under similar conditions. Comparison with literature data suggests a significant difference between samples living in aquaria and those grown in natural conditions. Finally, we investigate ancient (fossil) carbonate material and foraminifera extracted from marine sedimentary records. Different leaching procedures were tested using various HCl molarities. Results indicate that carbonate preferential dissolution must be carried out at an acid molarity < 0.18 mol l^?1. Possible contamination from silicate minerals can be verified using the Al/Ca ratio, but the threshold value strongly depends on the carbonate δ⁷Li value. When the silicate/carbonate ratio is high in the sediment sample (typically > 2), contamination from silicates cannot be avoided, even at low HCl molarity (? 0.1 mol l^?1). Finally, bulk carbonate and foraminifera extracted from the same core sample exhibited significant discrepancies: δ⁷Li values of foraminifera were more reproducible but were significantly lower. They were also associated with lower Sr/Ca and higher Mn/Ca ratios, suggesting a higher sensitivity to diagenesis, although specific vital effects cannot be fully ruled out.