Geostandards and Geoanalytical Research最新文献

Tungsten (W) isotopes are useful tools in geological and cosmochemical research, but the chemical separation of W is cumbersome for high-precision measurement. Here, a novel alkali (sodium hydroxide, NaOH) precipitation method for separation and purification of W in geological samples is described, which simplifies the chemical procedure. The amphoteric character of W is exploited to separate it from most matrix elements in alkaline conditions. Subsequently, TEVA resin was applied to further purify W for measurements using a multi-collector inductively coupled plasma-mass spectrometer. Importantly, the introduction of a certain amount of Na in the W analyte can increase the signal intensity by approximately 1.6 times, which may be caused by Coulomb fission. Such Na-triggered signal enhancement reduces the test portion mass required for analysis. Our results show that the Alfa Aesar W standard solution and geological reference materials JB-3, BCR-2 and BHVO-2 yield ¹⁸²W/¹⁸⁴W ratios consistent with previously reported values within uncertainty. Repeated measurement of the Alfa Aesar W standard solution shows that the intermediate precision of ¹⁸²W/¹⁸⁴W was better than 5 ppm (2s), which is sufficient to identify subtle ¹⁸²W isotope variations in terrestrial and extra-terrestrial samples. Above all, the alkali precipitation method in this study optimises the experimental process and mass spectrometric analysis.

We present the results of a study to generate reference glasses that reflect an environment analogous to historic nuclear fallout samples of interest for post-detonation nuclear forensics. The glasses were generated by melting and then quenching SiO₂, Al₂O₃ and CaCO₃ powders. Two suites of glasses with three distinct U isotopic ratios were successfully made with enrichments in the ²³⁵U isotope (~ natural [0.72%], ~ 53% and 94%), but the bulk elemental data showed heterogeneity (~ 10% RSD) with U mass fractions ranging from 331.47 to 373.63 μg g^-1. Spatially resolved U isotopic measurements were performed using three mass spectrometry techniques (secondary ion mass spectrometry-single stage accelerator mass spectrometry [SIMS-SSAMS], large geometry [LG] - SIMS, and laser ablation-inductively coupled plasma-mass spectrometry [LA-ICP-MS]) across five National Laboratories. The results showed good agreement with the bulk U isotopic data for the low, medium, and high U mass fractions. We conclude that despite elemental heterogeneity, these samples can serve as useful working reference materials for spatially resolved nuclear fallout analyses, as well as for other related spatially resolved analyses.

Carbonate clumped isotope, quantified by Δ₄₇ value, has wide application potential in Earth science. A recently proposed carbonate standardisation scheme based on community-available reference materials (i.e., ETH-1–4) has proven to improve interlaboratory comparability in Δ₄₇ measurement. However, the shortage of these reference materials may be problematic in future; therefore, developing traceable and supplementary in-house reference materials may become necessary, especially when supplies run out. Here, we describe a method of producing synthetic witherite carbonates with variable bulk isotopic compositions and clumped isotope ordering states, for which Δ₄₇ values were determined together with ETH carbonate reference materials. Results indicate that the witherite carbonates allow effective corrections for instrumental linearity and scale variations, improving long-term reproducibility. Additionally, by normalising witherite Δ₄₇ values to agreed ETH carbonate values on the Intercarb-Carbon Dioxide Equilibrium Scale, the witherite reference materials can be used to determine Δ₄₇ values without using equilibrated gases and reduce the consumption of ETH carbonates.

An interlaboratory comparison (ILC) was organised to characterise ⁸⁷Sr/⁸⁶Sr isotope ratios in geological and industrial reference materials by applying the so-called conventional method for determining ⁸⁷Sr/⁸⁶Sr isotope ratios. Four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC-1), one limestone (IAG CGL ML-3) and one slate (IAG OU-6) reference materials were selected, covering a wide range of naturally occurring Sr isotopic signatures. Thirteen laboratories received aliquots of these six reference materials together with a detailed technical protocol. The consensus values for the six reference materials and their associated measurement uncertainties were obtained by applying a Gaussian, linear mixed effects model fitted to all the measurement results. By combining the consensus values and their uncertainties with an uncertainty contribution for potential heterogeneity, reference values ranging from 0.708134 mol mol^-1 to 0.729778 mol mol^-1 were obtained with relative expanded uncertainties of ≤ 0.007 %. This study represents an ILC on conventional ⁸⁷Sr/⁸⁶Sr isotope ratios, within which metrological principles were considered and the compatibility of measurement results obtained by MC-ICP-MS and by MC-TIMS is demonstrated. The materials characterised in this study can be used as reference materials for validation and quality control purposes and to estimate measurement uncertainties in conventional ⁸⁷Sr/⁸⁶Sr isotope ratio measurement.

Laser ablation tandem mass spectrometry is a burgeoning field for in situ Rb-Sr geochronology. Here, we determined simultaneous isotope ratios of ⁸⁷Sr/⁸⁶Sr and ⁸⁷Rb/⁸⁶Sr in metamorphic biotite from western Maine, using an ESL™ imageGEO™193 excimer laser ablation system coupled to a Thermo Scientific™ Neoma™ MC-ICP-MS/MS. Measurements were made on Faraday cups with Rb⁺ at mass 87; Sr isotopes were reacted with SF₆ gas and measured as SrF⁺ at masses 103–107. Twenty-two laser spots in biotite from a single sample yield a "traditional" Rb-Sr isochron date of 289 ± 6 Ma. Time-resolved signals reveal significant zoning in ⁸⁷Sr/⁸⁶Sr and ⁸⁷Rb/⁸⁶Sr within single spot analyses, which were used to construct single spot isochrons. Individual laser spots contain multiple isochronous subpopulations; some spots contain up to three distinct Rb-Sr isochrons that are decoupled from variations in Rb/Sr. Thirty-five isochron dates were determined using this "sub-spot" approach, with ⁸⁷Sr/⁸⁶Sr intercepts that systematically vary with Rb-Sr date; two-point isochrons were calculated for individual integrations (n = 780) based on these variable intercepts. Both methods yield age peaks at 303, 270 and 240 Ma. These data suggest that the Rb-Sr system has the potential to record multiple heating, cooling or fluid-alteration events spanning ~ 100 My within small domains in single biotite crystals.

The mass fractions of Cl, Br and I were obtained by radiochemical neutron activation analysis (RNAA) of seventeen USGS geochemical reference materials (RMs), for which we had published halogen contents in GGR (Sekimoto and Ebihara 2017). Except for three RMs, 100 mg to > 300 mg of each powder material was used for a single analysis. After 10 min of neutron irradiation, a rapid radiochemical purification procedure was performed. Chemical yields were determined by the reactivation method. Each RM was analysed multiple times and consistent values were obtained for each element. Of the seventeen RMs, CLB-1, DGPM-1 and QLO-1a were also analysed by INAA. The INAA and RNAA results for CLB-1 and DGPM-1agree within 4%, implying that RNAA values obtained in this study are reliable. Compared with the 2017 data, the Cl and Br values obtained in this study were consistent, but the I values were 1/4 to 1/8 lower for all samples. It is concluded that the quantitative values of Cl and Br published in GGR in 2017 are reliable, while the I values are incorrect. Therefore, it is recommended that the I contents in the USGS RMs determined in this study be substituted in place of previous values.

Determination of alkali elements is important to Earth scientists, yet suitable and reliable microanalytical reference materials are lacking. This paper proposes a new albite reference material and evaluates the potential for future K-feldspar reference materials. The proposed Piz Beverin albite reference material from Switzerland yields a homogeneous composition at the centimetre- to micrometre-scale for Si, Al and Na with < 2000 μg g^-1 total trace elements (mostly heterogeneously distributed Ca, K and Sr). EPMA and LA-ICP-MS measurements confirm a composition of 99.5(2)% albite component, which is supported further by bulk XRF measurements. A round robin evaluation involving nine independent EPMA laboratories confirms its composition and homogeneity for Si, Al and Na. In addition, a set of five distinct clear K-feldspar samples was evaluated as possible reference materials. The first two crystals of adular and orthoclase yield unacceptable inhomogeneities with > 2% relative local variations of Na, K and Ba contents. The three other investigated sets of K-feldspar crystals are yellow sanidine crystals from Itrongay (Madagascar). Despite distinct compositions, EPMA confirms they are each homogeneous at the centimetre to micrometre scale for Si, Al and K and have no apparent inclusions; further investigation to find larger amounts of these materials is therefore justified.

Reported data for Lu, Hf mass fractions and ¹⁷⁶Hf/¹⁷⁷Hf isotopic ratios of mafic-ultramafic rock reference materials (RMs) are rare at present, hampering the comparison of data quality between difference laboratories. Herein, we measured the Lu and Hf mass fractions and the ¹⁷⁶Hf/¹⁷⁷Hf isotopic ratios of ten mafic-ultramafic rock RMs, including OKUM (komatiite), WPR-1 (serpentinised peridotite), NIM-N (norite), NIM-P (pyroxenite), UB-N (serpentinised peridotite), JP-1 (peridotite), NIM-D (dunite), MUH-1 (serpentinised harzburgite), HARZ01 (harzburgite), DTS-2b (dunite), which contain extremely low amounts of Lu and Hf (Lu, 2–150 ng g⁻¹; Hf, 5–500 ng g⁻¹). All measurements were conducted on a Neptune Plus multi-collector inductively coupled plasma-mass spectrometer employing an Aridus II desolvator inlet system and Jet sample/X skimmer cone configuration. The following RMs, OKUM, WPR-1, UB-N, JP-1, NIM-D, HARZ01 and DTS-2b, have ¹⁷⁶Hf/¹⁷⁷Hf precision of less than 60 ppm (2s) at test portions of 0.06 to 0.3 g, and are good ultramafic RMs for Lu-Hf systems. In contrast, significant Hf mass fraction and isotopic variability were observed in NIM-N, NIM-P and MUH-1 at test portion masses of 0.1 to 0.3 g. Collectively, our study provides a new database that can be used by the geochemical community for evaluating the Lu-Hf system of mafic-ultramafic rocks.

A new reference material, STDGL3, for the calibration of in situ analyses of sulfide minerals by LA-ICP-MS has been developed and characterised. It represents a lithium-borate-based glass containing a mixture of Zn- and Fe-sulfide concentrates doped with several chalcophile elements as well as Zr, Gd, Hf and Ta required for assessing common interferences on Ag, Au and Pt. STDGL3 has a wider range of elements and a better homogeneity compared with existing reference materials for LA-ICP-MS analysis of sulfides. Compositional variations for most elements are below 3% RSD, below 5% RSD for Ag, Au and Pt, and below 7% RSD for Se, when performing spot analyses with a 50 μm beam size. Its preparation recipe is reproducible allowing for multiple batches to be made. Use of STDGL3 significantly improves accuracy of sulfide mineral analysis by LA-ICP-MS when compared with use of other available reference materials. Performance of STDGL3 was evaluated using several different laser systems. No significant change was observed between 193 nm ArF excimer lasers with 5 and 20 ns pulse widths, but use of 213 and 248 nm lasers displays more systematic differences, especially when analysing galena. Correction coefficients are needed for some elements (Zn and Cd in particular) when analysing sulfide minerals using STDGL3 as a calibration reference material.