Accurate and High‐Precision Determination of Boron Isotopic Ratios at Low Concentration by MC‐ICP‐MS (Neptune)

We report an approach for the accurate and reproducible measurement of boron isotope ratios in natural waters using an MC‐ICP‐MS (Neptune) after wet chemistry sample purification. The sample matrix can induce a drastic shift in the isotopic ratio by changing the mass bias. It is shown that, if no purification is carried out, the direct measurement of a seawater diluted one hundred times will induce an offset of ?7‰ in the isotopic ratio, and that, for the same concentration, the greater the atomic mass of the matrix element, the greater the bias induced. Whatever the sample, it is thus necessary to remove the matrix. We propose a method adapted to water samples allowing purification of 100 ng of boron with a direct recovery of boron in 2 ml of 3% v/v HNO₃, which was our working solution. Boron from the International Atomic Energy Agency IAEA‐B1 seawater reference material and from the two groundwater reference materials IAEA‐B2 and IAEA‐B3, was chemically purified, as well as boron from the certified reference material NIST SRM 951 as a test. The reproducibility of the whole procedure (wet chemistry and MC‐ICP‐MS measurement) was ± 0.4‰ (2s). Accuracy was verified by comparison with positive‐TIMS values and with recommended values. Seawater, being homogeneous for boron isotope ratios, is presently the only natural water material that is commonly analysed for testing accuracy worldwide. We propose that the three IAEA natural waters could be used as reference samples for boron isotopes, allowing a better knowledge of their isotopic ratios, thus contributing to the certification of methods and improving the quality of the boron isotopic ratio measurements for all laboratories.     

Multi-Elemental Analysis of ATHO-G Rhyolitic Glass (MPI-DING Reference Material) by Femtosecond and Nanosecond LA-ICP-MS: Evidence for Significant Heterogeneity of B,V, Zn,Mo, Sn,Sb, Cs,W, Pt and Pb at the Millimetre Scale

This paper reports on the application of variants of LA-ICP-MS – including infrared femtosecond laser ablation (fs-LA) inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) and nanosecond laser ablation (ns-LA) coupled with single-collector sector-field (SF-) ICP-MS – to the in situ determination of trace elements in different splits of the reference material (RM) ATHO-G (MPI-DING). Analyses of the materials performed by fs- and ns-LA-ICP-MS demonstrated the efficiency of the techniques with typical accuracy at a level of ≤ ± 20%. One ‘anomalous’ split, however, displayed a significant discrepancy from the reference concentrations for B, V, Zn, Mo, Sn, Sb, Cs, W and Pb. Three- to six-fold enrichment of V, Mo, Cs and Pt relative to the reference contents in this split is likely to have been due to direct contact of the silicate melt with Pt crucible walls and ceramics. Boron, Zn, Sn, Sb, W and Pb depletion relative to the reference concentrations is probably due to siderophile element adsorption by the Pt walls and/or related to the formation of volatile-depleted compositional cords during the preparation process. Our results imply that additional precautions should be taken against volatile/siderophile element heterogeneity in marginal/surface layers (≤ 10 mm) during the preparation of RMs by the fusion technique.     

Producing Certified Reference Materials at the Central Geological Laboratory of Mongolia

This paper briefly outlines the production and certification of reference materials at the Central Geological Laboratory (CGL) of Mongolia. The marketing of CRMs produced in Mongolia, as well as problems encountered in internationally recognised certification attempts and some proposed solutions, are discussed. The basic elements of the CGL’s strategy for the development of the CRM sector are to produce high quality CRMs according to the requirements of internationally recognised norms, to consider the market needs, to certify the RMs at the international level and to widely advertise them to the geochemical community. The CGL has already established the basis for the further development of this sector by, for instance, accreditation under ISO/IEC 17025, by modernising its preparation technology, by cooperation with international organisations in the field of CRMs and by permanent participation in the International Association of Geoanalysts’ GeoPT™ proficiency testing programme.     

Mineralogical and Chemical Composition of International Carbon and Oxygen Isotope Calibration Material NBS 19, and Reference Materials NBS 18, IAEA-CO-1 and IAEA-CO-8

International carbon and oxygen isotope calibration material NBS 19 and reference materials NBS 18, International Atomic Energy Agency (IAEA)-CO-1 and IAEA-CO-8 are prepared from naturally occurring rock specimens of marble and carbonatite. Mineralogical and chemical analysis showed that only NBS 19 and IAEA-CO-1 represent essentially pure samples of calcite containing < and minimal (< 1%) quantities of quartz. In contrast, both NBS 18 and IAEA-CO-8, although primarily composed of calcite, are contaminated by a range of additional phases. NBS 18 was estimated to contain 1% Fe-dolomite and trace (< 1%) quantities of apatite and quartz. IAEA-CO-8 was estimated to contain at least 4% non-carbonate material (including apatite, barite, biotite and magnetite). NBS 18 and IAEA-CO-8 are both derived from samples of carbonatite and the calcite component of each material is characterised by appreciable substitution of Mg + Mn + Sr ± Fe ± Ba (Σ ≈ 14000–15000 μg g^-1) for Ca. The observations reported in this study complement data in the literature detailing significant grain-scale isotopic heterogeneity in NBS 18 and IAEA-CO-8. Both data sets highlight the need for careful characterisation of calibration materials prior to distribution.     

Precise Determination of Sm and Nd Concentrations and Nd Isotopic Compositions in Highly Depleted Ultramafic Reference Materials

In this study, a high‐precision method for the determination of Sm and Nd concentrations and Nd isotopic composition in highly depleted ultramafic rocks without a preconcentration step is presented. The samples were first digested using the conventional HF + HNO₃ + HClO₄ method, followed by the complete digestion of chromite in the samples using HClO₄ at 190–200 °C and then complete dissolution of fluoride formed during the HF decomposition step using H₃BO₃. These steps ensured the complete digestion of the ultramafic rocks. The rare earth elements (REEs) were separated from the sample matrix using conventional cation‐exchange chromatography; subsequently, Sm and Nd were separated using the LN columns. Neodymium isotopes were determined as NdO⁺, whereas Sm isotopes were measured as Sm⁺, both with very high sensitivity using single W filaments with TaF₅ as an ion emitter. Several highly depleted ultramafic rock reference materials including USGS DTS‐1, DTS‐2, DTS‐2b, PCC‐1 and GSJ JP‐1, which contain extremely low amounts of Sm and Nd (down to sub ng g^?1 level), were analysed, and high‐precision Sm and Nd concentration and Nd isotope data were obtained. This is the first report of the Sm‐Nd isotopic compositions of these ultramafic rock reference materials except for PCC‐1.     

SLRS‐5 Elemental Concentrations of Thirty‐Three Uncertified Elements Deduced from SLRS‐5/SLRS‐4 Ratios

The fifth version of natural river water certified reference material, SLRS‐5 (National Research Council – Conseil National de Recherches Canada), is commonly used to control the quality of major and trace element measurements. Concentrations of silicon and thirty‐one uncertified trace elements have been reported for the certified reference material SLRS‐4, but they are not yet available for SLRS‐5. Here, SLRS‐5/SLRS‐4 ratios were deduced from SLRS‐5 and SLRS‐4 measurements by inductively coupled plasma‐atomic emission spectrometry and high‐resolution inductively coupled plasma‐mass spectrometry for certified elements and thirty‐five uncertified elements (rare earth elements, B, Bi, Br, Cs, Ga, Ge, Hf, Li, Nb, P, Pd, Rb, Rh, S, Sc, Si, Sn, Th, Ti, Tl, Y). Both reference materials were measured directly one after the other, so that calculated elemental ratios would not be notably influenced either by calibration uncertainties or by eventual long‐term instrumental drift. The computed ratios are in good agreement with those deduced from the certified values. We also report concentrations for thirty‐three uncertified elements in SLRS‐5 by combining the measured SLRS‐5/SLRS‐4 ratios and the published SLRS‐4 values. The resulting new data set provides target SLRS‐5 values, which will be useful in quality control procedures.     

Zinc Isotopic Compositions of NIST SRM 683 and Whole‐Rock Reference Materials

In this study the homogeneity of the zinc isotopic composition in the NIST SRM 683 reference material was examined by measuring the Zn isotopic signature in microdrilled sample powders from two metal nuggets. Zinc was purified using AG MP‐1M resin and then measured by MC‐ICP‐MS. Instrumental mass bias was corrected using the “sample‐standard bracketing” method and empirical external normalisation with Cu doping. After evaluating the potential effects of varying acid mass fractions and different matrices, high‐precision Zn isotope data were obtained with an intermediate measurement precision better than ± 0.05‰ (δ⁶⁶Zn, 2s) over a period of 5 months. The δ⁶⁶Zn_JMC‐Lyon mean values of eighty‐four and fourteen drilled powders from two nuggets were 0.11 ± 0.02‰ and 0.12 ± 0.02‰, respectively, indicating that NIST SRM 683 is a good isotopic reference material with homogeneous Zn isotopes. The Zn isotopic compositions of seventeen rock reference materials were also determined, and their δ⁶⁶Zn values were in agreement with most previously published data within 2s. The δ⁶⁶Zn values of most of the rock reference materials analysed were in the range 0.22–0.36‰, except for GSP‐2 (1.07 ± 0.06‰, n = 12), NOD‐A‐1 (0.96 ± 0.03‰, n = 6) and NOD‐P‐1 (0.78 ± 0.03‰, n = 6). These comprehensive data should serve as reference values for quality assurance and interlaboratory calibration exercises.     

How Fit Are Your Data?

Most laboratories aim to produce data of the highest quality. Trying to lower uncertainties to infinitesimal figures and push detection limits even lower are valid goals. However, is it possible to overachieve? Are old data still of good enough quality to be usable? In a geochemical context, the main goal of producing analytical results is to answer geological or environmental questions. Not all scientific problems require the same data quality. What is really required are data of adequate quality – i.e., ‘fit-for-purpose’– to ensure that the geological problem at hand can be solved. Furthermore, it is doubtful that uncertainties and reproducibilities associated with field sampling are better than those from laboratories. It is thus proposed that, as geoanalysts, we encourage data users (students, colleagues or referees) to ensure that their analytical results are of sufficient quality to solve the problem. However, authors have to demonstrate, through the use of reproducibility testing, reference and quality control materials, that the quality of their results is sufficient to solve the problem. Uncertainties and detection limits in publications should not only be evaluated with respect to a set value, such as 10%, but also with regard to the geological problem to be solved.     

High‐Precision Iron Isotope Analysis of Geological Reference Materials by High‐Resolution MC‐ICP‐MS

We report high‐precision iron isotopic data for twenty‐two commercially available geological reference materials, including silicates, carbonatite, shale, carbonate and clay. Accuracy was checked by analyses of synthetic solutions with known Fe isotopic compositions but different matrices ranging from felsic to ultramafic igneous rocks, high Ca and low Fe limestone, to samples enriched in transition group elements (e.g., Cu, Co and Ni). Analyses over a 2‐year period of these synthetic samples and pure Fe solutions that were processed through the whole chemistry procedure yielded an average δ⁵⁶Fe value of ?0.001 ± 0.025‰ (2s, n = 74), identical to the expected true value of 0. This demonstrates a long‐term reproducibility and accuracy of < 0.03‰ for determination of ⁵⁶Fe/⁵⁴Fe ratios. Reproducibility and accuracy were further confirmed by replicate measurements of the twenty‐two RMs, which yielded results that perfectly match the mean values of published data within quoted uncertainties. New recommended values and associated uncertainties are presented for interlaboratory calibration in the future.