Preliminary Characterisation of New Reference Materials for Microanalysis: Chinese Geological Standard Glasses CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5

Four silicate glasses were prepared by the fusion of about 1 kg powder each of a basalt, syenite, soil and andesite to provide reference materials of natural composition for microanalytical work. These glasses are referred to as ‘Chinese Geological Standard Glasses’ (CGSG) ‐1, ‐2, ‐4 and ‐5. Micro and bulk analyses indicated that the glasses are well homogenised with respect to major and trace elements. Some siderophile/chalcophile elements (e.g., Sn, Pt, Pb) may be heterogeneously distributed in CGSG‐5. This paper provides the first analytical data for the CGSG reference glasses using a variety of analytical techniques (wet chemistry, XRF, EPMA, ICP‐AES, ICP‐MS, LA‐ICP‐MS) performed in nine laboratories. Most data agree within uncertainty limits of the analytical techniques used. Discrepancies in the data for some siderophile/chalcophile elements exist, mainly because of possible heterogeneities of these elements in the glasses and/or analytical problems. From the analytical data, preliminary reference and information values for fifty‐five elements were calculated. The analytical uncertainties [2 relative standard error (RSE)] were estimated to be between about 1% and 20%.     

Determination of Reference Values for NIST SRM 610–617 Glasses Following ISO Guidelines

We present new reference values for the NIST SRM 610–617 glasses following ISO guidelines and the International Association of Geoanalysts’ protocol. Uncertainties at the 95% confidence level (CL) have been determined for bulk‐ and micro‐analytical purposes. In contrast to former compilation procedures, this approach delivers data that consider present‐day requirements of data quality. New analytical data and the nearly complete data set of the GeoReM database were used for this study. Data quality was checked by the application of the Horwitz function and by a careful investigation of analytical procedures. We have determined quantitatively possible element inhomogeneities using different test portion masses of 1, 0.1 and 0.02 μg. Although avoiding the rim region of the glass wafers, we found moderate inhomogeneities of several chalcophile/siderophile elements and gross inhomogeneities of Ni, Se, Pd and Pt at small test portion masses. The extent of inhomogeneity was included in the determination of uncertainties. While the new reference values agree with the NIST certified values with the one exception of Mn in SRM 610, they typically differ by as much as 10% from the Pearce et al. (1997) values in current use. In a few cases (P, S, Cl, Ta, Re) the discrepancies are even higher.     

Suitability of Mn‐ and Fe‐Rich Reference Materials for Microanalytical Research

Manganese‐ and iron‐rich materials are of major geoscientific and economic interest, many of which contain microscopic features that provide valuable information. To obtain accurate results, a homogeneous microanalytical reference material for calibration is needed. Several researchers have used the Mn‐ and Fe‐rich RMs, JMn‐1, NOD‐A‐1, NOD‐P‐1 and FeMn‐1, for this purpose; therefore, they were tested in this study to determine their suitability for microanalysis. Their homogeneity was investigated by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) with two different types of lasers (nano‐ and femtosecond), with spot and line scan analyses and with different operating parameters, such as spot size, pulse repetition rate and fluence. As the established manganese nodule RMs revealed inhomogeneities for picogram to microgram test portions, we also investigated the new synthetic Fe‐ and Mn‐rich RM, FeMnOx‐1. FeMnOx‐1 was found to be homogeneous for large (ø 40 μm: 2% RSD repeatability) and small (ø 8–10 μm: 10% RSD repeatability) spot sizes. This homogeneity is in the range of the homogeneous NIST SRM 610 and GSE‐1G reference glasses. Furthermore, FeMnOx‐1 revealed a large‐scale homogeneity within uncertainties of a few per cent, using test portions in the ng range, when measuring four individual mounts of this material.     

Characterisation of Apatites as Potential Uranium Reference Materials for Fission‐track Dating by LA‐ICP‐MS

We report homogeneity tests on large natural apatite crystals to evaluate their potential as U reference materials for apatite fission‐track (AFT) thermochronology by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). The homogeneity tests include the measurements of major element concentrations by electron probe microanalysis (EPMA), whereas for U concentration, isotope dilution (ID) ICP‐MS and laser ablation (LA) ICP‐MS were employed. Two apatite crystals are potential reference materials for LA‐ICP‐MS analysis: a 1 cm³ fraction of a Durango crystal (7.5 μg g^?1 U) and a 1 cm³ Mud Tank crystal (6.9 μg g^?1 U). The relative standard deviation (1 RSD) of the U concentration determined by ID‐ICP‐MS of both apatite crystals was ≤ 1.5%, whereas 1 RSD for the LA‐ICP‐MS results was better than 4%, providing sufficient homogeneity for fission‐track dating. The results on the U homogeneity for two different apatite samples are an important step towards establishing in situ dating routines for AFT analysis by LA‐ICP‐MS.     

Reference Values Following ISO Guidelines for Frequently Requested Rock Reference Materials

We present new reference values for nineteen USGS, GSJ and GIT‐IWG rock reference materials that belong to the most accessed samples of the GeoReM database. The determination of the reference values and their uncertainties at the 95% confidence level follows as closely as possible ISO guidelines and the Certification Protocol of the International Association of Geoanalysts. We used analytical data obtained by the state‐of‐the‐art techniques published mainly in the last 20 years and available in GeoReM. The data are grouped into four categories of different levels of metrological confidence, starting with isotope dilution mass spectrometry as a primary method. Data quality was checked by careful investigation of analytical procedures and by the application of the Horwitz function. As a result, we assign a new and more reliable set of reference values and respective uncertainties for major, minor and a large group of trace elements of the nineteen investigated rock reference materials.     

A Practical Method for Accurate Measurement of Trace Level Fluorine in Mg‐ and Fe‐Bearing Minerals and Glasses Using Electron Probe Microanalysis

Fluorine plays an important role in magmatic and hydrothermal processes, but due to its low abundance in geological samples determining F is difficult by electron probe microanalysis. By using a W‐Si multi‐layered pseudocrystal as the diffraction crystal instead of thallium acid phthalate (TAP), count rates were considerably higher, which however introduced spectral interferences between FKα and FeLα and MgKβ lines when normal integral mode is applied. In this study, we developed a protocol using a W‐Si multi‐layered pseudocrystal for measuring accurately trace level F in both minerals and glasses. First, we used differential mode with an optimised PHA (pulse height analysis) setting in signal processing, instead of normal integral mode, which completely eliminated the second‐order MgKβ line. Second, the overlap of the first‐order FeLα on FKα peak, which cannot be filtered by modifying the PHA setting, was calibrated quantitatively using F‐free minerals and silicate glasses. Applying this two‐step method, F was determined in a number of reference glasses, as well as in glasses synthesised from powders of the rock reference materials AC‐E, GS‐N and DR‐N. Our data are consistent within error with F concentrations determined by other methods, demonstrating the reliability of this method.     

High‐Precision Fe and Mg Isotope Ratios of Silicate Reference Glasses Determined In Situ by Femtosecond LA‐MC‐ICP‐MS and by Solution Nebulisation MC‐ICP‐MS

In this study, a technique for high precision in situ Fe and Mg isotope determinations by femtosecond‐laser ablation‐multi collector‐ICP‐MS (fs‐LA‐MC‐ICP‐MS) was developed. This technique was employed to determine reference values for a series of common reference glasses that may be used for external standardisation of in situ Fe and Mg isotope determinations in silicates. The analysed glasses are part of the MPI‐DING and United States Geological Survey (USGS) reference glass series, consisting of basaltic (BIR‐1G, BCR‐2G, BHVO‐2G, KL2‐G, ML3B‐G) and komatiitic (GOR128‐G and GOR132‐G) compositions. Their Fe and Mg isotope compositions were determined by in situ fs‐LA‐MC‐ICP‐MS and by conventional solution nebulisation multi‐collector ICP‐MS. We determined δ⁵⁶Fe values for these glasses ranging between ‐0.04‰ and 0.10‰ (relative to IRMM‐014) and δ²⁶Mg values ranging between ‐0.40‰ and ‐0.15‰ (relative to DSM‐3). Our fs‐LA‐MC‐ICP‐MS results for both Fe and Mg isotope compositions agreed with solution nebulisation analyses within analytical uncertainties. Furthermore, the results of three USGS reference glasses (BIR‐1G, BHVO‐2G and BCR‐2G) agreed with previous results for powdered and dissolved aliquots of the same reference materials. Measurement reproducibilities of the in situ determinations of δ⁵⁶Fe and δ²⁶Mg values were usually better than 0.12‰ and 0.13‰ (2s), respectively. We further demonstrate that our technique is a suitable tool to resolve isotopic zoning in chemically‐zoned olivine crystals. It may be used for a variety of different applications on isotopically‐zoned minerals, e.g., in magmatic or metamorphic rocks or meteorites, to unravel their formation or cooling rates.     

Precise Determination of Silicon Isotopes in Silicate Rock Reference Materials by MC‐ICP‐MS

A HF‐free sample preparation method was used to purify silicon in twelve geological RMs. Silicon isotope compositions were determined using a Neptune instrument multi‐collector‐ICP‐MS in high‐resolution mode, which allowed separation of the silicon isotope plateaus from their interferences. A 1 μg g^‐1 Mg spike was added to each sample and standard solution for online mass bias drift correction. δ³⁰Si and δ²⁹Si values are expressed in per mil (‰), relative to the NIST SRM 8546 (NBS‐28) international isotopic RM. The total variation of δ³⁰Si in the geological reference samples analysed in this study ranged from ‐0.13‰ to ‐0.29‰. Comparison with δ²⁹Si values shows that these isotopic fractionations were mass dependent. IRMM‐17 yielded a δ³⁰Si value of ‐1.41 ± 0.07‰ (2s, n = 12) in agreement with previous data. The long‐term reproducibility for natural samples obtained on BHVO‐2 yielded δ³⁰Si = ‐0.27 ± 0.08‰ (2s, n = 42) on a 12 month time scale. An in‐house Si reference sample was produced to check for the long‐term reproducibility of a mono‐elemental sample solution; this yielded a comparable uncertainty of ± 0.07‰ (2s, n = 24) over 5 months.     

Determination of Thallium in the USGS Glass Reference Materials BIR‐1G,BHVO‐2G and BCR‐2G and Application to Quantitative Tl Concentrations by LA‐ICP‐MS

Here, we present determinations of thallium (Tl) concentrations in the USGS reference materials BIR‐1G, BHVO‐2G and BCR‐2G measured by solution ICP‐MS. The Tl content in these three glasses spans a range of about 2–230 ng g^?1, which is similar to the values published for the respective powder materials. The determined range of Tl concentrations in these three glass reference materials makes them ideal for investigating Tl concentrations in basaltic and andesitic volcanic glasses. We also performed a series of laser ablation ICP‐MS measurements on the three samples, which show that this technique is able to determine Tl concentrations in glass samples with concentrations as low as 2 ng g^?1.     

New Thorium Isotope Ratio Measurements in Silicate Reference Materials: A‐THO,AGV‐2, BCR‐2, BE‐N,BHVO‐2 and BIR‐1

A two‐step Th isolation protocol, involving micro‐columns of TRU‐Spec extraction chromatography material and AG1 resin, was evaluated. The MC‐ICP‐MS procedure included ²³²Th tailing characterisation and correction, and calibrator bracketing using an in‐house standard solution (ThS1) to correct for instrumental mass bias and Faraday cup to secondary electron multiplier relative gain. Repeated analyses of reference solutions (UCSC Th ‘A’, WUN, OU Th ‘U’, IRMM‐36) were consistent with published data. Six reference materials (A‐THO, BCR‐2, AGV‐2, BHVO‐2, BE‐N and BIR‐1) were processed. The average ²³⁰Th/²³²Th values obtained for these samples are in excellent agreement with published data. In addition, we report the first ²³⁰Th/²³²Th values for BE‐N and BIR‐1. The intermediate precisions for rock samples ranged from ± 0.24 to ± 0.49% (2 RSD) and were similar to those achieved for synthetic solutions, thereby supporting the overall validity of the chemical separation, data acquisition and reduction procedures. Counting statistics on the ²³⁰Th isotope was the most significant source of uncertainty. The intermediate precision of the mean ²³⁰Th/²³²Th for the Th‐depleted BIR‐1 (5.64 × 10^?6 ± 0.27%, 2 RSD) is in the range of the analyses of other reference materials analysed in this study.     

Determination of Cr,Cu, Ni,Sn, Sr and Zn Mass Fractions in Geochemical Reference Materials by Isotope Dilution ICP‐MS

Isotope dilution (ID) mass spectrometry is a primary method of analysis suited for the accurate and precise measurement of several trace elements in geological matrices. Here we present mass fractions and respective uncertainties for Cr, Cu, Ni, Sn, Sr and Zn in 10 silicate rock reference materials (BCR‐2, BRP‐1, BIR‐1, OU‐6, GSP‐2, GSR‐1, AGV‐1, RGM‐1, RGM‐2 and G‐3) obtained by the double ID technique and measuring the isotope ratios with an inductively coupled plasma‐mass spectrometer equipped with collision cell. Test portions of the samples were dissolved by validated procedures, and no further matrix separation was applied. Addition of spikes was designed to achieve isotope ratios close to unity to minimise error magnification factors, according to the ID theory. Radiogenic ingrowth of ⁸⁷Sr from the decay of ⁸⁷Rb was considered in the calculation of Sr mass fractions. The mean values of our results mostly agree with reference values, considering both uncertainties at the 95% confidence level, and also with ID data published for AGV‐1. Considering all results, the means of the combined uncertainties were < 1% for Sr, approximately 2% for Sn and Cu, 4% for Cr and Ni and almost 6% for Zn.     

Nickel Isotope Variations in Terrestrial Silicate Rocks and Geological Reference Materials Measured by MC‐ICP‐MS

Although initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass‐dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two‐stage chromatography procedure, Ni isotope ratios were measured by MC‐ICP‐MS and were corrected for instrumental mass bias using a double‐spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04‰, and intermediate measurement precision for NIST SRM 986 was 0.05‰ (2s). Igneous‐ and mantle‐derived rocks displayed a restricted range of δ^60/58Ni values between ?0.13 and +0.16‰, suggesting an average BSE composition of +0.05‰. Manganese nodules (Nod A1; P1), shale (SDO‐1), coal (CLB‐1) and a metal‐contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06‰, whereas komatiite‐hosted Ni‐rich sulfides varied from ?0.10 to ?1.03‰.     

Precise and Accurate In Situ Determination of Lead Isotope Ratios in NIST,USGS, MPI‐DING and CGSG Glass Reference Materials using Femtosecond Laser Ablation MC‐ICP‐MS

Lead isotope ratio data were obtained with good precision and accuracy using a 266 nm femtosecond laser ablation (fLA) system connected to a multi‐collector ICP‐MS (MC‐ICP‐MS) and through careful control of analytical procedures. The mass fractionation coefficient induced by 266 nm femtosecond laser ablation was approximately 28% lower than that by 193 nm excimer laser ablation (eLA) with helium carrier gas. The exponential law correction method for Tl normalisation with optimum adjusted Tl ratio was utilised to obtain Pb isotopic data with good precision and accuracy. The Pb isotopic ratios of the glass reference materials NIST SRM 610, 612, 614; USGS BHVO‐2G, BCR‐2G, GSD‐1G, BIR‐1G; and MPI‐DING GOR132‐G, KL2‐G, T1‐G, StHs60/80‐G, ATHO‐G and ML3B‐G were determined using fLA‐MC‐ICP‐MS. The measured Pb isotopic ratios were in good agreement with the reference or published values within 2s measurement uncertainties. We also present the first high‐precision Pb isotopic data for GSE‐1G, GSC‐1G, GSA‐1G and CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5 glass reference materials obtained using the femtosecond laser ablation MC‐ICP‐MS analysis technique.     

Spatial Geochemistry: A Characterisation of Heterogeneity in Reference Materials

Geochemical reference materials (RMs) for microbeam techniques are typically characterised by averages and dispersion statistics (e.g., standard deviation, variance) that are calculated for a number of measurements (beam shots). It is proposed that the mapping of RMs will add spatial information that better characterises the grouping and magnitudes of the heterogeneities and provides the information necessary to define a minimum analytical mass. A simple mathematical solution is proposed, which can be easily computed and understood. The analogous notions to sill and range from geostatistics are applied to the minimum analytical mass versus the relative standard deviation. To assess grouping and magnitudes of the heterogeneities, a ‘proximity number’ is computed for each average value ± ‘n’ standard deviations (magnitude). Different chemical anomalies have been simulated to demonstrate the behaviour of the proximity number. To further test the proposed spatial geochemistry concept, sulfide‐ and oxide‐bearing RMs have been selected because many are crippled with nugget effect. They have been mapped with a micro‐XRF apparatus, and results are presented for CHR‐Bkg, CHR‐Pt+, MASS‐1, MASS‐3, WMS‐1 and WMS‐1a. MASS‐1 and MASS‐3 are the most suitable RMs for microbeam techniques. Spatial geochemistry offers a new approach to better characterise reference materials.     

High‐Precision Measurement of Molybdenum Isotopic Compositions of Selected Geochemical Reference Materials

Here we describe high‐precision molybdenum isotopic composition measurements of geological reference materials, performed using multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS). Purification of Mo for isotopic measurements was achieved by ion exchange chromatography using Bio‐Rad AG^® 1‐X8 anion exchange resin. Instrumental mass bias was corrected using ¹⁰⁰Mo‐⁹⁷Mo double spiking techniques. The precision under intermediate measurement conditions (eighteen measurement sessions over 20 months) in terms of δ^98/95Mo was 0.10‰ (2s). The measurement output was approximately four times more efficient than previous techniques, with no compromise in precision. The Mo isotopic compositions of seven geochemical reference materials, seawater (IAPSO), manganese nodules (NOD‐P‐1 and NOD‐A‐1), copper‐molybdenum ore (HV‐2), basalt (BCR‐2) and shale (SGR‐1b and SCo‐1), were measured. δ^98/95Mo values were obtained for IAPSO (2.25 ± 0.09‰), NOD‐P‐1 (?0.66 ± 0.05‰), NOD‐A‐1 (?0.48 ± 0.05‰), HV‐2 (?0.23 ± 0.10‰), BCR‐2 (0.21 ± 0.07‰), SCo‐1 (?0.24 ± 0.06‰) and SGR‐1b (0.63 ± 0.02‰) by calculating δ^98/95Mo relative to NIST SRM 3134 (0.25‰, 2s). The molybdenum isotopic compositions of IAPSO, NOD‐A‐1 and NOD‐P‐1 obtained in this study are within error of the compositions reported previously. Molybdenum isotopic compositions for BCR‐2, SCo‐1 and SGR‐1b are reported for the first time.     

New ICP‐MS Results for Trace Elements in Five Iron‐Formation Reference Materials

Iron formations (IFs) typically contain low mass fractions of most trace elements, including the rare earth elements (REE), and few publications describe analytical methods dedicated to this matrix. In this study, we used bomb and table‐top acid dissolution procedures and ICP‐MS to determine the mass fractions of trace elements in IF reference materials FER‐1, FER‐2, FER‐3, FER‐4 and IF‐G. The full digestion of the IF samples with the bomb procedure required the addition of a small amount of water together with the acids. The results obtained by this method mostly agreed statistically with published values. The most remarkable exception was the higher values obtained for the heavy REE in FER‐3. The recoveries of the REE obtained with the table‐top procedure were slightly higher than those of the bomb digestion, except for the values of the heavy REE in FER‐3 and FER‐4, which were up to 30% lower than published values. Sintering of the samples with sodium peroxide was performed to determine the REE, but the results tended to be lower than those derived following acid digestion. On the whole, the recoveries showed dependence on the conditions of digestion, but subtle differences in trace mineral composition between samples also exerted influence on the analytical results for trace elements.     

Non‐Matrix‐Matched Calibration for the Multi‐Element Analysis of Geological and Environmental Samples Using 200 nm Femtosecond LA‐ICP‐MS: A Comparison with Nanosecond Lasers

LA‐ICP‐MS is one of the most promising techniques for in situ analysis of geological and environmental samples. However, there are some limitations with respect to measurement accuracy, in particular for volatile and siderophile/chalcophile elements, when using non‐matrix‐matched calibration. We therefore investigated matrix‐related effects with a new 200 nm femtosecond (fs) laser ablation system (NWRFemto200) using reference materials with different matrices and spot sizes from 10 to 55 μm. We also performed similar experiments with two nanosecond (ns) lasers, a 193 nm excimer (ESI NWR 193) and a 213 nm Nd:YAG (NWR UP‐213) laser. The ion intensity of the 200 nm fs laser ablation was much lower than that of the 213 nm Nd:YAG laser, because the ablation rate was a factor of about 30 lower. Our experiments did not show significant matrix dependency with the 200 nm fs laser. Therefore, a non‐matrix‐matched calibration for the multi‐element analysis of quite different matrices could be performed. This is demonstrated with analytical results from twenty‐two international synthetic silicate glass, geological glass, mineral, phosphate and carbonate reference materials. Calibration was performed with the certified NIST SRM 610 glass, exclusively. Within overall analytical uncertainties, the 200 nm fs LA‐ICP‐MS data agreed with available reference values.     

Refinement of Phosphorus Determination in Quartz by LA‐ICP‐MS through Defining New Reference Material Values

The aim of this study was to improve the quality of laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) determination of phosphorus in crystalline quartz. Over the last decade, the Geological Survey of Norway has routinely performed trace element determinations on quartz from both operating and potential quartz deposits by LA‐ICP‐MS. The determined phosphorus concentrations were, with but few exceptions, consistently within the range of 10 to 30 μg g^?1, results that seemed to be both too high and too consistent. The multi‐material calibration curve obtained from a suite of reference materials (NIST SRM 610, 612, 614, 1830, BAM No. 1 amorphous SiO₂ glass) did not define a precise regression line. Published phosphorus concentrations for the reference materials are poorly constrained and the observed dispersions along the multi‐material calibration curve suggest that some of the reference values may be inaccurate. Furthermore, the calibration curve did not pass through the origin of the [(cps ³¹P/cps ³⁰Si) · cone. Si] vs. P concentration diagram; thus, in addition to the uncertainties of the literature values of phosphorus, it is difficult to define the calibration curve. Three reference materials (NIST SRM 614, 1830, synthetic quartz KORTH) were sent for phosphorus accelerator implantation, providing an independent and accurate (± 3%) approach for determining phosphorus concentrations in crystalline quartz. The intrinsic phosphorus concentrations of the three implanted samples plus those for NIST SRM 610 and 612 were determined by secondary ion mass spectrometry (SIMS), yielding new phosphorus values for NIST SRM 610, 612, 614 and 1830. Using these new values resulted in a better defined LA‐ICP‐MS calibration curve. However, the source of the ICP‐MS related background could not be defined, such that it must still be empirically corrected for.     

Multi‐Element Determination of Trace Elements in Natural Water Reference Materials by ICP‐SFMS after Tm Addition and Iron Co‐precipitation

We report on an improved method for determining trace element abundances in seawater and other natural waters. The analytical procedure involves co‐precipitation on iron hydroxides after addition of a Tm spike, and measurement by inductively coupled plasma‐sector field mass spectrometry (ICP‐SFMS). The validity of the method was assessed through a series of co‐precipitation experiments, using ultra‐diluted solutions of a certified rock reference material (BIR‐1). Results obtained for four natural water reference materials (NASS‐5, CASS‐4, SLEW‐3, SLRS‐4) are in agreement with published working values for rare earth elements, yttrium, vanadium and, when available, for hafnium, zirconium, thorium and scandium. A set of proposed values with uncertainties typically better than 8% RSD is proposed for Hf, Zr and Th.     

Flux‐Free Fusion of Silicate Rock Preceding Acid Digestion for ICP‐MS Bulk Analysis

We present a new method for the decomposition of silicate rocks by flux‐free fusion in preparation for whole‐rock trace element determination (Sc, Rb, Sr, Y, Zr, Nb, Cs, Ba, rare earth elements and Hf) that is especially applicable to zircon‐bearing felsic rocks. The method was verified by analyses of RMs of mafic (JB‐1a, JB‐2, JGb‐1) and felsic rocks (JG‐3, JR‐3, JSd‐1, GSP‐2, G‐2). Pellets of powdered sample (up to 500 mg) without flux were weighed and placed in a clean platinum crucible. The samples were then fused in a Siliconit® tube furnace and quenched to room temperature. The optimum condition for the fusion of granitic rock was determined to be heating for 2–3 min at 1600 °C. The fused glass in the platinum crucible after heating was decomposed using HF and HClO₄ in a Teflon® beaker. Decomposed and diluted sample solutions were analysed using a quadrupole inductively coupled plasma‐mass spectrometer. Replicate analyses (n = 4 or 5) of the RMs revealed that analytical uncertainties were generally < 3% for all elements except Zr and Hf (～ 6%) in JG‐3. These higher uncertainties may be attributed to sample heterogeneity. Our analytical results for the RMs agreed well with recommended concentrations and recently published concentrations, indicating complete decomposition of our rock samples during fusion.