Geostandards and Geoanalytical Research最新文献

Advances in multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) have led to the widespread use of iron (Fe) isotopes to elucidate the (bio)geochemical history of a range of environments. To generate Fe isotope ratio measurements, standard-sample bracketing (SSB) is commonly used to correct for instrumental mass bias inherent to MC-ICP-MS. However, SSB is only accurate when sample and isotope standard Fe concentrations match, in addition to the bulk solution matrix. When the Fe concentrations differ, Fe isotope ratio measurement results may be inaccurate, a phenomenon known as the "self-induced matrix effect." This study systematically characterised the self-induced matrix effect for dry plasma Fe isotope ratio measurements on three MC-ICP-MS instruments and three introduction systems. Our extensive dataset indicates that: (1) the degree of mass bias is consistent regardless of MC-ICP-MS front-end design, (2) the degree of mass bias becomes less reproducible as the concentration difference between the sample and bracketing standard increases, and (3) this applies to both pure Fe solutions and solutions from geological materials. This study reinforces the requirement to match bracketing standard and sample concentrations within 10% and provides a correction method for that fall beyond the recommended concentration range to subsequently allow for proper concentration matching during SSB.

To help understand bioapatite microstructures and related chemical variations, their impact on O-isotope compositions measured and give insights on sample preparation, this study analysed conodonts and shark teeth prepared in different orientations through microanalytical and bulk sampling techniques: scanning electron microscopy (SEM); electron probe microanalysis (EPMA); continuous-flow and high-temperature reduction – isotope ratio mass spectrometry; and secondary ion mass spectrometry (SIMS). The SEM and EPMA measurements in conodonts allowed to distinguish the tissues commonly analysed by SIMS, which included albid and hyaline crowns but given their often small-scale intergrowth, mixtures of these are difficult to avoid. In situ SIMS O-isotope analyses provided different δ¹⁸O values: lower values with higher variance (16 ± 1‰ n = 13, 15.7 ± 1.9‰ n = 11) for mixed albid-hyaline tissues, and higher, homogeneous values (17.1 ± 0.2‰, n = 13) for mainly hyaline tissues. Recent shark teeth δ¹⁸O_SIMS value for dentine of the same tooth was 10‰ lower than the mean δ¹⁸O_SIMS value for enameloid whereas the δ¹⁸O_PO4 values measured for enameloid and dentine using the HTR method were identical. The variation of δ¹⁸O seems sensitive to analytical artefacts related to sample textures, caused during the sample preparation over more porous biomineral surfaces.

An analytical method to accurately determine trace levels of Se and Te is essential to meet the growing importance of these elements to Earth science research. Herein, an in-house assembled photochemical vapour generation (PVG) unit, instead of normal sample nebulisation, with inductively coupled plasma-mass spectrometry (ICP-MS), was developed for the detection of Se and Te in geological samples. The major parameters that might potentially influence the PVG efficiencies of Se(IV) and Te(IV) were investigated. The unit could fully generate volatile species under 30 s of ultraviolet irradiation in the presence of 15% v/v formic acid, 15% v/v acetic acid and 50 mg l^-1 of Co²⁺. Under optimised conditions, the limit of detections (LODs, 3s, n = 11) of the proposed method were 0.5 ng l^-1 for Se and 0.6 ng l^-1 for Te. The RSDs of Se and Te were 2.0% and 2.3% (1 μg l^-1, n = 7), respectively. Interference experiments showed that Fe, Ti, V and Cu have certain negative effects, so the standard addition method was used for real sample analysis. Measurement results for eleven CRMs, including soils (GSS-4, GSS-7), sediments (GSD-9, GSD-10) and rocks (GSR-1, GSR-2, GSR-3, GSR-5, AGV-2, GSP-2 and W-2a), were consistent with literature values, and showed better precision, indicating the feasibility of the proposed method for determination of trace Se and Te in geological samples.

Lithium isotope measurement in spodumene by femtosecond LA-MC-ICP-MS was investigated and the influence of plasma operating conditions and data reduction strategy on accuracy and precision was studied. It was found that “hot” plasma conditions led to an unstable baseline signal and substantial variations in the Li isotope ratios. By adding a constant amount of water to the carrier gas, a stable baseline was achieved and isotope ratios became reproducible and were consistent with data from solution-based MC-ICP-MS. The resulting biases were within ± 0.51‰ and the reproducibility was better than 0.09‰. Comparison of Li isotope ratios resulting from different data evaluation schemes showed that the mean of the transient intensity ratios, integration of the entire or a user-defined period of the ion signals resulted in good agreement with solution-based data, while linear regression underestimated the Li isotope ratios. It was also found that “cool” plasma operation produced a stable baseline signal, but the Li isotope results were biased by up to -4.3%, irrespective of water introduction and the data evaluation scheme. With the optimised “hot-wet” conditions, the Li isotope ratios in eleven spodumene materials were determined which successfully allowed distinguishing regional deposits and partially veins of the available samples.

The sulfur (S) mass fraction of carbonate minerals can be used to reconstruct the environmental conditions and S sources at the time of precipitation. As S is present in a wide range of host materials, there is an urgent need to develop a method to extract S from a single mineral phase. We have developed a method to extract structurally substituted sulfate, termed carbonate-associated sulfate (CAS), from geological and biogenic carbonate minerals using weakly acidic cation exchange resins. Two types of weakly acidic cation exchange resin (methacrylic acid and acrylic acid types) were tested to minimise the blank S contents and decompose carbonate. After repeated cleaning of the resins with high-purity water or HCl, the blank S contents were reduced to < 0.1 μg, which is < 0.1% of the CAS in the samples. The cleaned resin was used to dissolve 10 and 25 mg of the JCp-1 carbonate certified reference material (CRM; Japanese National Institute of Advanced Industrial Science and Technology, AIST). Samples and resin were added to 8 ml of high-purity water at resin/sample ratios of 2, 5, 10 and 20, set on a shaking table, and reacted. The supernatant solutions were sampled sequentially from 0.5 h to 87 h after the start of experiments. The results show that the optimal conditions for decomposing 10 mg of carbonate is a resin/sample ratio of ≥ 10 with a reaction time of ≥ 40 h. Carbonate-associated S mass fractions were measured for six geological and biogenic carbonate CRMs. The coefficient of variation in carbonate-associated S mass fractions was ≤ 7%, regardless of the type of resins used. The mass fractions determined with this method recover 74–94% of the total S mass fractions reported in previous studies, suggesting that this method dissolved carbonate, and did not leach other S-bearing fractions that are not resistant to weak acids. Another benefit of this method is that the decomposed solution can be introduced directly into the ion chromatograph, allowing for more sensitive analyses. We emphasise that this method can also be used for S isotopic measurements, as S contamination from other S-bearing mineral phases is low.

The multi-collector inductively coupled plasma-mass spectrometer is an instrument suited to measuring sulfur isotopes in all types of samples, from ice cores and river waters to carbonates and Archaean rocks. Its main advantage is the more convenient method of sample preparation, as sulfate does not need to be reduced but purified from the sample through ion exchange. This method allows the measurement of unbiased and precise δ³⁴S values from samples as small as 10-nmol with a typical intermediate precision of 0.15‰ (2s) at 95% confidence. So far, no attempt has been made to understand at which levels of analytical precision and bias MC-ICP-MS could provide ∆³³S values. Here, the first standard addition experiment undertaken for ∆³³S evaluation shows that measurement results on a Neptune Plus MC-ICP-MS allows us to calculate ∆³³S values identical to those established by other measurement principles, for samples down to 30 nmol S, with an intermediate precision as good as 0.05‰ (2s). Though this precision is not as good as the analytical precision of data acquired by the SF₆ method, the advantages of small sample size and straightforward sample handling make it a very useful tool for investigating past and modern aspects of the sulfur cycle.

This Geostandards and Geoanalytical Research Bibliographic Review 2022 presents an overview of a wide range of publications in 2022 focusing on the characterisation of new geoanalytical reference materials (RMs) as well as studies which published measurement results for established RMs. The development of highly accurate new methods and techniques leads to large new analytical data sets for RMs with improved accuracy and precision, which we present in this review.

Secondary ion mass spectrometry was used to test the δ¹⁸O and δ³⁴S nanogram-scale homogeneity of a suite of candidate sulfate minerals, ultimately selecting three barite, two anhydrite, and two gypsum samples from the Royal Ontario Museum that have repeatabilities for their SIMS measurements of better than ±0.39‰ and ±0.37‰ (1s) for oxygen and sulfur isotope ratios, respectively. Metrological splits of each of the seven materials were sent to multiple gas source isotope ratio mass spectrometry laboratories in order to establish their absolute ¹⁸O/¹⁶O and ³⁴S/³²S ratios. The inter-laboratory results of GS-IRMS analyses yielded reasonably narrow ranges in δ¹⁸O_VSMOW, whereas larger variations in δ³⁴S_VCDT values were found between the results from the gas source laboratories. All samples have good reproducibility within laboratories of GS-IRMS 10³δ¹⁸O values of between ±0.24‰ and ±0.44‰ (1s). The reproducibility within laboratories of GS-IRMS 10³δ³⁴S values range from ±0.07‰ to ±0.99‰ (1s). Here we also discuss some of the current analytical limitations affecting these isotope-mineral systems. A total of 256 metrological splits have been prepared from each of these seven materials; these aliquots will be made available to the global geochemical community.

We present high precision negative ion thermal ionisation mass spectrometry (N-TIMS) Os isotope measurement results for the DROsS isotope reference material (iCRM), to investigate the limits on the precision of TIMS-based ¹⁸⁶Os/¹⁸⁸Os results. We used analytical conditions previously highlighted to optimise precision, present a new flexible data processing protocol, and measured ¹⁸⁴Os intensities on a Faraday Cup equipped with an amplifier using a 10¹² Ω resistor. Despite a measurement procedure that minimised uncertainty contributions from counting statistics and Johnson-Nyquist noise, the intermediate measurement precision of our approach does not significantly improve on previous high precision Os isotope measurements, with the exception of ¹⁸⁴Os/¹⁸⁸Os. This is probably due to uncertainties in measured amplifier gain factors, which are greater when using mixed arrays of 10¹¹ and 10¹² Ω resistors than when using 10¹¹ Ω resistors alone, though Faraday Cup deterioration could also contribute. We propose that multi-dynamic Os isotope measurements could largely eliminate both of these uncertainties. Our ¹⁸⁴Os/¹⁸⁸Os measurement results are the most precise yet, yielding ¹⁸⁴Os/¹⁸⁸Os = 0.0013036 ± 0.0000007 (2s, n = 38). Additionally, we average our data with published data to recommend the following isotope ratios for DROsS: ¹⁸⁶Os/¹⁸⁸Os = 0.1199319 ± 0.0000024, ¹⁸⁷Os/¹⁸⁸Os = 0.1609227 ± 0.0000022, ¹⁸⁹Os/¹⁸⁸Os = 1.219709 ± 0.000010, ¹⁹⁰Os/¹⁸⁸Os = 1.983793 ± 0.000011.

Various methods have been developed to extract a primary seawater Sr isotope signal from carbonate rocks for strontium isotope stratigraphy. However, there is little consensus around the best method due to variable sample purity and mineralogy. For this study, we applied sequential leaching to a range of rock samples in order to explore strontium isotope leaching systematics of less favoured argillaceous and dolomitic limestone samples. Following an ammonium acetate (NH₄Ac) prewash that removed ~ 10% of the carbonate fraction, a subsequent dilute acetic acid leach (10–30% aliquot) was shown to extract the lowest, demonstrably least altered seawater ⁸⁷Sr/⁸⁶Sr isotope ratios, along with in most cases seawater-like rare earth element (REE) plus yttrium (Y) patterns with the highest Y/Ho ratios (mostly > 36). Subsequent dissolution steps exhibited significantly elevated ⁸⁷Sr/⁸⁶Sr isotope ratios, Rb/Sr, Al/Ca and Mg/Ca ratios, indicating greater contributions from aluminosilicates and dolomite in the leachates. The new dissolution method by comparison significantly increases the likelihood of obtaining primary seawater ⁸⁷Sr/⁸⁶Sr isotope ratios from argillaceous and dolomitic limestones where the other established procedures failed. Broad application of this approach could improve the temporal resolution of the seawater Sr isotope curve, especially where high purity limestone samples are scarce.