Recent advances enable in situ(87)Sr/Sr-86 analysis of geological materials at micrometre-scale using LA-Q-ICP-MS/MS, which employs reaction gases to eliminate isobaric interferences. However, single-detector quadrupole ICP-MS typically yields lower precision than multi-collector systems because isotopes are measured sequentially rather than simultaneously. Improving LA-Q-ICP-MS/MS Sr-87/Sr-86 precision would enhance its applicability in many geological and environmental scenarios. Here, we assess the effects of laser repetition rate, laser fluence and spot size on measurement precision of Sr isotopes using LA-Q-ICP-MS/MS with N2O as reaction gas. Thirteen reference materials (RMs) comprising seven apatites (Durango, Emerald Lake, Madagascar, McClure, Mud Tank, Otter Lake and 401) and six silicate glasses (NIST SRM 610, NIST SRM 612, USGS BCR-2G, USGS BHVO-2G, USGS BIR-1G, USGS GSD-1G) were analysed by systematically varying laser repetition rate, fluence and spot diameter. Our results show that increasing laser repetition rate improves signal intensity and stability, resulting in enhanced analytical precision. After mass bias correction, Sr-87/Sr-86 precision improved from > 4 parts per thousand at 10 Hz to < 3 parts per thousand at 20 Hz (1s). Notably, 20 Hz exceeds the 5-10 Hz commonly used in most LA-ICP-MS Sr isotope studies. The positive correlation between repetition rate and precision was observed in both apatite and glass RMs. Although analyses conducted at 5 J cm(-2) produce higher Sr-88 counts than those at 3 J cm(-2), both fluences show similar improvements in Sr-87/Sr-86 precision with increasing spot diameter. While both larger spot sizes and higher repetition rates increased signal intensity, the latter yields more stable signals. For LA-Q-ICP-MS/MS measurement of Sr-87/Sr-86 in apatite and similar geological materials, repetition rates >= 12 Hz are recommended under conditions tested here. Among the glasses, USGS BHVO-2G yielded the best and most consistent analytical uncertainty, indicating its suitability as a reference material for Sr isotope measurement.
Triple oxygen isotope ratios of waters are commonly reported on the VSMOW-SLAP scale, whereas comparison with theoretical calculations and assessment of instrumental scale distortion require accurate constraints on the measured isotopic compositions of the primary isotopic reference materials (iRMs) themselves. In particular, the measured delta 17OVSMOW and Delta ' 17OVSMOW values for SLAP and its substitute, SLAP2, remain insufficiently constrained and reported values differ among laboratories. Here, we measured triple oxygen isotope ratios for two primary iRMs (VSMOW and SLAP) and twelve secondary iRMs (VSMOW2, SLAP2, GISP, GRESP, USGS45, USGS46, USGS46a, USGS47, USGS48, USGS49, USGS50 and USGS53) using BrF5 fluorination and dual-inlet isotope-ratio mass spectrometry. For SLAP, we obtained delta 18OVSMOW = -55.50 +/- 0.15 parts per thousand and delta 17OVSMOW = -29.66 +/- 0.08 parts per thousand, giving Delta ' 17OVSMOW = 34 +/- 6 per meg (all expanded uncertainties, k = 2). The corresponding values for SLAP2 agree within uncertainty. When expressed on the conventional VSMOW-SLAP scale, our Delta ' 17OVSMOW-SLAP values for all secondary iRMs with available literature values agree with previously published values within uncertainty, confirming interlaboratory comparability on that scale. In contrast, waters with low delta 18O values, Delta ' 17OVSMOW values are systematically higher than the corresponding Delta ' 17OVSMOW-SLAP values. These results further suggest that accurate determination of the VSMOW-scale isotopic composition of SLAP and/or SLAP2 across laboratories is essential, particularly for low-delta 18O samples, for which the difference between VSMOW-scale and VSMOW-SLAP-scale Delta ' 17O values becomes large, and for meaningful comparison between measured data and theoretical calculations.
The oxidation state of Fe serves as a direct indicator of oxygen fugacity in geological systems. We present new results of electron probe microanalysis (EPMA) flank method for determining Fe 2+ /ΣFe ratios in garnet, amphibole, and biotite, using a field‐emission microprobe equipped with TAPL diffraction crystal. For each mineral group, the Fe 2+ mass fractions exhibit a linear correlation with the intensity ratios measured at the flank positions of Fe L α and Fe L β , albeit with distinct slopes and intercepts. The flank positions of Fe L α and Fe L β , which theoretically correspond to minimal Fe 3+ L 3 absorption and maximal Fe 2+ L 2 absorption, are constrained using two synthetic ferric and ferrous garnet end‐members. Eight newly collected natural garnets, for which the Fe 2+ /ΣFe ratios have been measured by an independent method of wet‐chemistry or Mössbauer spectroscopy, constitute a useful set of reference materials with FeO T mass fractions ranging from 3 to 39% m/m for calibrating the EPMA flank method. Additionally, we re‐analysed the amphibole and biotite reference materials proposed by Li et al . (2019, Chem. Geol., 509, 152–162). The Fe 2+ /ΣFe ratios obtained using our EPMA flank method exhibited small bias relative to reference values, with deviations below 0.05 for garnet, amphibole and biotite in most cases.
Determination of platinum‐group elements (PGE), rhenium (Re) and gold (Au) in geological materials remains analytically demanding because of their low mass fractions, heterogeneous distribution and occurrence in refractory mineral phases. This review evaluates fire assay and digestion‐based strategies for Pt, Pd, Rh, Ir, Ru, Os, Re and Au, with emphasis on matrix‐dependent workflow selection and laboratory implementation. Fire assay is advantageous when larger test portions are required to reduce subsampling uncertainty, whereas Carius tube and high‐pressure asher digestion can provide lower procedural blanks and compatibility with isotope dilution and Re‐Os measurement. HF‐assisted digestion and alkaline fusion may be necessary for silicate‐bound or chromite‐hosted refractory phases. The review examines collector systems, post‐fusion dissolution, coprecipitation, chromatographic purification, Os separation, ICP‐MS/MS interference control and emerging fire assay‐LA‐ICP‐MS approaches. No single workflow is universally superior: performance depends on analyte suite, mineralogy, test portion mass, procedural blank, decomposition efficiency, recovery, instrumental interferences and intended data use. Accordingly, practical selection criteria are proposed for routine PGE‐Au determination, expanded PGE‐Re‐Au determination, Re‐Os applications, Os isotope ratio measurement and refractory geological materials. Validation requirements – including blank assessment, recovery, bias, precision, detection capability and measurement uncertainty – are integrated into the proposed workflow framework.
Quantifying sulfur (S) speciation in apatite‐group minerals (apatites) is critically important for understanding magmatic and magmatic‐hydrothermal processes but has generally been restricted to individual analytical techniques. In this study, we have quantified sulfur speciation in a suite of apatites (including fluorapatite, hydroxylapatite and chlorapatite) using three complementary analytical techniques: S K ‐edge X‐ray absorption near‐edge structure (XANES), S 2 p X‐ray photoelectron spectroscopy (XPS), and S K α wavelengths with electron probe micro analysis (EPMA). Our results show that all three techniques identify S 6+ as the dominant sulfur species, with minor contributions from S 4+ , in the apatite samples investigated in this study. Sulfur K ‐edge XANES offers the most precise quantification of S 6+ /ΣS values (where ΣS = S 6+ + S 4+ + S 2‐ ) from 0.93 to 1.0, with the standard deviation from ±0.01 to ±0.06, although it requires synchrotron access and careful calibration. Sulfur 2 p XPS analyses yield a similar trend in S speciation but lower S 6+ /ΣS values from 0.69 to 0.78, attributable to partial radiation‐induced reduction of S 6+ to S 4+ related to prolonged X‐ray exposure. Similarly, the EPMA‐based (S K α wavelength shift) technique is capable of distinguishing between S 6+ and S 4+ , and yields S 6+ /ΣS values ranging from 0.56 to 0.88, again indicating significant radiation‐induced reduction. Therefore, the XPS and EPMA‐based techniques are also capable of quantifying sulfur speciation in apatites but require accurate corrections for radiation‐induced sulfur reduction. This study highlights the strengths and limitations of these three analytical techniques, with XANES offering the highest sensitivity. At the same time, XPS and EPMA, although less sensitive, are surface‐specific and widely accessible, respectively. It also guides their applications for quantifying sulfur speciation in apatites.
