BAM‐S005 Type A and B: New Silicate Reference Glasses for Microanalysis

To test whether the silicate reference glasses BAM‐S005‐A and BAM‐S005‐B from BAM (The Federal Institute for Materials Research and Testing, Germany) are suitable materials for microanalysis, we investigated the homogeneity of these reference glasses using the microanalytical techniques EPMA, LA‐ICP‐MS and SIMS. Our study indicated that all major and most trace elements are homogeneously distributed at micrometre sampling scale in both types of glass. However, some trace elements (e.g., Cs, Cl, Cr, Mo and Ni) seem to be inhomogeneously distributed. We also determined the composition of BAM‐S005‐A and BAM‐S005‐B. The EPMA data of major elements confirmed the information values specified by the certificate. With the exception of Sr, Ba, Ce and Pb, our trace element data by LA‐ICP‐MS were also in agreement with the certified values within the stated uncertainty limits. The reasons for the discrepancy in these four elements are still unclear. In addition, we report new data for twenty‐two further trace elements, for which the concentrations were not certified. Based on our investigation, we suggest that both of these materials are suitable for many microanalytical applications.     

Determination of Trace Elements in Geological Reference Materials G‐3, GSP‐2 and SGD‐1a by Low‐Dilution Glass Bead Digestion and ICP‐MS

We present a revised alkali fusion method for the determination of trace elements in geological samples. Our procedure is based on simple acid digestion of powdered low‐dilution (flux : sample ≈ 2 : 1) glass beads where large sample dilution demanded by high total dissolved solids, a main drawback of conventional alkali fusion, could be circumvented. Three geological reference materials (G‐3 granite, GSP‐2 granodiorite and SGD‐1a gabbro) decomposed by this technique and routine tabletop acid digestion were analysed for thirty trace elements using a quadrupole ICP‐MS. Results by conventional acid digestion distinctly showed poor recoveries of Zr, Hf and rare earth elements due to incomplete dissolution of resistant minerals. On the other hand, results obtained by our method were in reasonable agreement with reference data for most analytes, indicating that refractory minerals were efficiently dissolved and volatile loss was insignificant.     

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.     

Uranium and Thorium Concentration and Isotopic Composition in Five Glass (BHVO‐2G,BCR‐2G,NKT‐1G,T1‐G,ATHO‐G) and Two Powder (BHVO‐2, BCR‐2) Reference Materials

Here we report uranium and thorium isotopic ratios and elemental concentrations measured in solid reference materials from the USGS (BHVO‐2G, BCR‐2G, NKT‐1G), as well as those from the MPI‐DING series (T1‐G, ATHO‐G). Specifically created for microanalysis, these naturally‐sourced glasses were fused from rock powders. They cover a range of compositions, elemental concentrations and expected isotopic ratios. The U‐Th isotopic ratios of two powdered source materials (BCR‐2, BHVO‐2) were also characterised. These new measurements via multi‐collector thermal ionisation mass spectrometry and multi‐collector inductively coupled plasma‐mass spectrometry can now be used to assess the relative performance of techniques and facilitate comparison of U‐Th data amongst laboratories in the geoscience community for in situ and bulk analyses.     

Lithium Isotope Composition of Ultramafic Geological Reference Materials JP‐1 and DTS‐2

An organic solvent‐free two‐step column procedure is presented that provided robust, high yield and super clean separation of Li from silicate rock sample matrices. The measured δ⁷Li value for BHVO‐2 of +4.29 ± 0.23‰ (1s) is comparable with the reported values. The δ⁷Li values for GSJ JP‐1 (+3.14 ± 0.41‰, 1s) and USGS DTS‐2 (+4.91 ± 0.34‰, 1s) presented here provide new reference values for ultramafic rock reference materials.     

Determination of Ga,Ge, Mo,Ag, Cd,In, Sn,Sb, W,Tl and Bi in USGS Whole‐Rock Reference Materials by Standard Addition ICP‐MS

A procedure for determining a wide range of chalcophile and siderophile elements in typical crustal rocks using standard addition and ICP‐SFMS (inductively coupled plasma sector field mass spectrometry) is presented. New results for Ga, Ge, Mo, Ag, Cd, In, Sn, Sb, W, Tl and Bi abundances in USGS whole‐rock reference materials AGV‐2, BHVO‐1, BIR‐1, G‐2, GSP‐1 and W‐2 are reported using this analytical procedure. Intermediate precision of means based on multiple dissolved aliquots of each USGS reference material was 10% RSD or better for Ga, Ge, In and Sn in all, and similarly good for Ag, Cd, Sb, Tl and Bi in most reference materials. Poorer intermediate precision of Mo and W measurements in several reference materials is probably due to higher analytical blanks on these elements and powder heterogeneity due to a sulfide‐related nugget effect in the specific case of Mo in GSP‐1. Results for all elements fell within the range of available published data with the exception of Ag, which yielded systematically higher concentrations than found in the literature for five of the six reference materials, likely reflecting interference from unresolved polyatomic species.     

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.     

An Investigation of Digestion Methods for Trace Elements in Bauxite and Their Determination in Ten Bauxite Reference Materials Using Inductively Coupled Plasma‐Mass Spectrometry

Trace elements from samples of bauxite deposits can provide useful information relevant to the exploration of the ore‐forming process. Sample digestion is a fundamental and critical stage in the process of geochemical analysis, which enables the acquisition of accurate trace element data by ICP‐MS. However, the conventional bomb digestion method with HF/HNO₃ results in a significant loss of rare earth elements (REEs) due to the formation of insoluble AlF₃ precipitates during the digestion of bauxite samples. In this study, the digestion capability of the following methods was investigated: (a) ‘Mg‐addition’ bomb digestion, (b) NH₄HF₂ open vessel digestion and (c) NH₄F open vessel digestion. ‘Mg‐addition’ bomb digestion can effectively suppress the formation of AlF₃ and simultaneously ensure the complete decomposition of resistant minerals in bauxite samples. The addition of MgO to the bauxite samples resulted in (Mg + Ca)/Al ratios ≥ 1. However, adding a large amount of MgO leads to significant blank contamination for some transition elements (V, Cr, Ni and Zn). The NH₄HF₂ or NH₄F open vessel digestion methods can also completely digest resistant minerals in bauxite samples in a short period of time (5 hr). Unlike conventional bomb digestion with HF/HNO₃, the white precipitates and the semi‐transparent gels present in the NH₄HF₂ and NH₄F digestion methods could be efficiently dissolved by evaporation with HClO₄. Based on these three optimised digestion methods, thirty‐seven trace elements including REEs in ten bauxite reference materials (RMs) were determined by ICP‐MS. The data obtained showed excellent inter‐method reproducibility (agreement within 5% for REEs). The relative standard deviation (% RSD) for most elements was < 6%. The concentrations of trace elements in the ten bauxite RMs showed agreement with the limited certified (Li, V, Cr, Cu, Zn, Ga, Sr, Zr and Pb) and information values (Co, Ba, Ce and Hf) available. New trace element data for the ten RMs are provided, some of which for the first time.     

Platinum‐Group Element Results for Two Cobalt‐Rich Seamount Crust Ultra‐Fine Reference Materials: MCPt‐1and MCPt‐2

Two Co‐rich seamount crust reference materials, MCPt‐1 and MCPt‐2, were prepared using ultra‐fine particle size milling technique and characterised for the platinum‐group elements (PGEs). The raw material for these two reference materials was collected separately from the Magellan seamounts of the western Pacific Ocean and the seamounts of the central Pacific Ocean by Russian and Chinese scientists. First, they were ground by ball mill to a ?200 mesh powder, then further processed by ultra‐fine jet mill and well‐mixed. The particle size distributions of the samples were tested by a laser particle analyser; the average particle size was 1.8 and 1.5 μm (equal to about 2000 mesh) respectively. The homogeneity of six major and minor elements in these two materials was tested at the milligram level of sampling mass by high‐precision wavelength dispersive X‐ray fluorescence (XRF) spectrometry and at the microgram level of sampling mass by electron probe microanalyser. The homogeneity of more than forty trace elements, including Pt, was tested at the microgram level of sampling mass by LA‐ICP‐MS. Except for Rh, all PGEs were determined by isotope dilution‐ICP‐MS. Platinum in MCPt‐1 and MCPt‐2 was characterised as certified values, whereas the other five PGEs in MCPt‐1 and MCPt‐2 were reported as reference values. In addition, the information values of sixty‐two major, minor and trace elements were obtained by XRF, ICP‐AES and ICP‐MS. The minimum sampling mass for the determination of PGEs was 1 g, while the minimum sampling mass for the determination of the other elements was 2–5 mg.     

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.     

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.     

Preparation and Characterisation of Two Geochemical Reference Materials: DG‐H (Granite) and AM‐H (Amphibolite) from the Himalayan Orogenic Belt

Two geochemical reference materials of Himalayan origin named DG‐H (a granite) and AM‐H (an amphibolite) prepared by the Wadia Institute of Himalayan Geology Dehradun are described. Both samples were collected from the NW Himachal Himalaya in India. With the participation of analysts from more than forty international laboratories, element determination data collected during the past 10 years for characterisation of the samples was processed to assign working values using statistical procedures in use for this purpose. Earlier work published on these samples is incorporated in the present communication making it an updated document. The typical chemical and petrological characteristics of these two samples may prove useful for method validation and calibration of analytical instruments used for analysing similar rock types, and for widening the analytical range of several analytical methods used for geochemical analysis.     

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.     

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.     

A Compilation of Silicon,Rare Earth Element and Twenty‐One other Trace Element Concentrations in the Natural River Water Reference Material SLRS‐5 (NRC‐CNRC)

The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given.     

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.     

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.     

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.     

Barium Isotopic Compositions of Geological Reference Materials

The interest in variations of barium (Ba) stable isotope amount ratios in low and high temperature environments has increased over the past several years. Characterisation of Ba isotope ratios of widely available reference materials is now required to validate analytical procedures and to allow comparison of data obtained by different laboratories. We present new Ba isotope amount ratio data for twelve geological reference materials with silicate (AGV‐1, G‐2, BHVO‐1, QLO‐1, BIR‐1, JG‐1a, JB‐1a, JR‐1 and JA‐1), carbonate (IAEA‐CO‐9) and sulfate matrices (IAEA‐SO‐5 and IAEA‐SO‐6) relative to NIST SRM 3104a. In addition, two artificially fractionated in‐house reference materials BaBe12 and BaBe27 (δ^137/134Ba = ?1.161 ± 0.049‰ and ?0.616 ± 0.050‰, respectively) are used as quality control solutions for the negative δ‐range. Accuracy of our data was assessed by interlaboratory comparison between the University of Bern and the United States Geological Survey (USGS). Data were measured by MC‐ICP‐MS (Bern) and TIMS (USGS) using two different double spikes for mass bias correction (¹³⁰Ba–¹³⁵Ba and ¹³²Ba–¹³⁶Ba, respectively). MC‐ICP‐MS measurements were further tested for isobaric and non‐spectral matrix effects by a number of common matrix elements. The results are in excellent agreement and suggest data accuracy.     

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.