The Design of Re‐usable Carius Tubes for the Determination of Rhenium,Osmium and Platinum‐Group Elements in Geological Samples

The traditional Carius tube technique is cumbersome and requires skilful work to seal the Carius tube, which can be used only once. We describe a modification to the technique that does not require the use of a high‐temperature welding torch to melt the Carius tube to seal it. The newly designed Carius tube consists of a main body with a 3 mm‐thick glass wall, a neck and head with walls 4 mm in thickness, and an efficient screw‐thread stopper. These new features allowed the tube to be used repeatedly. We demonstrate relatively low procedural blanks derived for Re and Os, and platinum‐group elements (PGEs), using the redesigned tube. A temperature of 220 °C could be reached for about 5 ml of HNO₃ for a 47 ml tube and for 32 ml of inverse aqua regia for a 200 ml tube. This digestion technique can be used for routine analysis of Re and PGEs in geological samples.     

Efficiency of a re-usable Carius tube for determination of platinum group elements in ultramafic rocks

Digestion with aqua regia in Carius tube is commonly employed for determination of PGEs in geological samples. However, silicates cannot be completely dissolved by aqua regia and PGEs might partially remain in silicate residue. In this study, an ultramafic reference material was used to investigate the efficiencies of a new re-usable Carius tube after digestion at 220 and 240℃, and an autoclave-lined Carius tube at 260 and 280℃. The results show that about 10% of PGEs retained in the silicate residues at 220 and 5% still r℃ emains even digestion temperature increases to 280℃. These results agree with previous works that increasing the digestion pressure and temperature can achieve more effective dissolution. Thus, a modified digestion procedure for determination of PGEs in ultramafic rocks by the re-usable Carius tube was proposed in this study.     

Reassessment of HF/HNO3 Decomposition Capability in the High‐Pressure Digestion of Felsic Rocks for Multi‐Element Determination by ICP‐MS

Complete dissolution is essential to obtain accurate analytical results for geological samples. Felsic rocks are known to be very difficult to dissolve because of the presence of refractory minerals such as zircon. In this study, we undertook a systematic evaluation of the effect of the HF/HNO₃ ratio, digestion time, digestion temperature, digested test portion mass and the presence of insoluble fluorides on analytical results for the felsic rock GSP‐2 using high‐pressure HF and HF/HNO₃ digestion. Digestion in mixtures of HF and HNO₃ acids is a commonly used method of dissolution for geological samples. However, our results clearly indicate that adding HNO₃ inhibited the digestion capabilities of HF for refractory minerals such as zircon. It took 8–12 hr for Zr to be completely recovered in GSP‐2 at 190 °C, whereas it needed about 36 and 72 hr at 160 and 140 °C, respectively. White precipitates were observed in the final solution for test portion mass > 100 mg, irrespective of which of the five different digestion solutions was used (1 ml HF, 2 ml HF, 1 ml HF + 0.5 ml HNO₃, 1 ml HF + 1 ml HNO₃ and 1.5 ml HF + 1.5 ml HNO₃). Environmental scanning electron microscopy showed that these precipitates were mainly composed of AlF₃. Instead of further HCl, HNO₃ or HClO₄ attack, we propose that using ultra‐fine samples and a small sample size is a good way to avoid the formation of insoluble residues (e.g., fluorides). To further investigate the precision and accuracy of the proposed method (using HF alone as the digestion solution during the first acid attack step), a suite of silicate rock reference materials was analysed. Most of the results were found to be in reasonable agreement with the reference values, with a relative error of < 10%.     

铼—锇同位素分析中试样化学预处理方法进展

评述了用于Re-Os同位素体系分析的化学前处理技术的发展。简要介绍了卡洛斯管熔样法、Os的CCl4提取、溴提取和微蒸馏方法。卡洛斯管封闭熔样方法，有效地防止了Os的挥发损失和保证了Os同位素平衡，是一种很有发展前景的熔样方法。蒸馏法仍是分离和纯化Os的有效方法，溶剂（CCl4)提取和溴提取法在许多实验室里应用，而微蒸馏则是Os的二次纯化的主要方法。Re的化学分离和纯化仍是离子交换和萃取法。引用主要文献29篇。     

Bias in the Determination of Zr,Y and Rare Earth Element Concentrations in Selected Silicate Rocks by ICP‐MS when Using Some Routine Acid Dissolution Procedures: Evidence from the GeoPT Proficiency Testing Programme

The analytical results for the modified river sediment, SdAR‐1 circulated in Round 31 of the GeoPT proficiency testing programme, revealed unexpected discrepancies for Zr, Y and most higher atomic number rare earth elements, in determinations made by ICP‐MS using acid attack digestion methods. This investigation compares these ICP‐MS results with those obtained for SdAR‐1 by three other methods: (a) ICP‐MS using fusion/sintering for sample digestion, (b) XRF analysis and (c) INAA. The distribution of results for the elements Rb, Sr, Ce, Y, Yb and Zr is examined and compared with those of the test material for Round 25 of GeoPT, Paraná basalt, HTB‐1. A substantial proportion (though not all) of Y, Yb and Zr determinations in SdAR‐1 by ICP‐MS/acid attack was variably low (sometimes very low) compared with other methods. A detailed evaluation of the procedures used to determine these results indicated that successful determinations by ICP‐MS/acid attack could be made if digestions were made at 180 °C for 48 hr using at least 2 ml HF per 100 mg of sample. We suggest that the more benign conditions (used by many laboratories) resulted in incomplete digestion of resistant minerals, such as zircon.     

Reassessment of Hydrofluoric Acid Desilicification in the Carius Tube Digestion Technique for Re–Os Isotopic Determination in Geological Samples

In this study, Re and Os isotopes were systematically determined in six geological reference materials (RMs; covering a wide range of lithologies) using the Carius tube (CT) digestion technique with and without hydrofluoric acid desilicification. Our results show that the HF desilicification increased the Re extraction efficiency (by 9–15%) evidenced from basaltic and andesitic rocks (e.g., BHVO‐2, TDB‐1 and AGV‐2). This implies that a small proportion of Re resides in silicate phases. For mafic–ultramafic rocks (e.g., BCR‐2, WGB‐1 and WPR‐1), Re extraction efficiencies obtained by the CT digestion with and without HF desilicification were similar. This may indicate that Re in these rocks may dominantly reside in some phases (e.g., magnetite and sulfides) that could be completely dissolved in aqua regia solutions without the aid of HF desilicification. Our results also show that the HF desilicification increased Os extraction efficiency (by 13–99%) in some RMs (e.g., BHVO‐2, WGB‐1 and AGV‐2). This observation suggests that a portion of Os‐rich trace phases may occur as inclusions in the silicate phases that act as isolators at ~ 200 mesh sizes. This study demonstrates that the HF desilicification step prior to CT digestion is important for complete extraction of Re and Os in geological samples.     

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.     

铼-锇同位素分析样品预处理研究进展

文章评述并归纳了近年来地质样品中Re-Os同位素分析的化学前处理方法研究进展。总结了锍镍火试金法、碱熔法、Carius管溶样法以及HPA-S高温高压釜溶样法等常用的Re-Os同位素样品消解方法。归纳了离子交换、溶剂萃取富集Re以及蒸馏、萃取等分离富集Os的方法。由于地质样品的复杂性,Re、Os含量的不均一性及测试方法的多样性,要求在具体分析过程中不同的样品使用不同的消解方法和分离富集方法。当前国内应用较成熟的Re、Os分离方法是Carius管逆王水分解样品,原位蒸馏或CCl4萃取方法分离Os,阴离子交换法或丙酮萃取分离Re。     

An Alternative Protocol for Single Zircon Dissolution with Application to (U‐Th‐Sm)/He Thermochronometry

Zircon (U‐Th‐Sm)/He (ZHe) thermochronometry is a powerful tool that has been widely used in geology to constrain the exhumation histories of orogens. In this study, we present an alternative protocol for dissolving zircon grains for determination of parent nuclides. This new alkali fusion procedure developed at the SARM (Service d'Analyse des Roches et des Minéraux) in Nancy, France, is fast (requiring only 2 d, including cleaning steps) and offers several advantages over conventional methods by avoiding: (i) use of HF pressure dissolution and (ii) complete removing of grains from the metal microvials. After dissolution, U, Th and Sm were measured using an ICP‐MS. We tested the new procedure on two different ZHe reference materials, the Fish Canyon Tuff and Buluk Tuff; these provided precision values for ZHe‐age estimations of 9 and 6% (1s), respectively. In addition, using this method, zircons from the Buluk Tuff are shown to be chemically more homogenous and more suitable for assessing the uncertainty of the entire integrated procedure.     

A Rapid Acid Digestion Technique for the Simultaneous Determination of Bromine and Iodine in Fifty‐Three Chinese Soils and Sediments by ICP‐MS

Bromine and iodine are important tracers for geochemical and environmental studies. In this study, a rapid acid digestion (HNO₃ + HF) with ammonia dilution for the simultaneous determination of bromine and iodine in soils and sediments using ICP‐MS was developed. The recoveries of Br and I were controlled by the synergic effect of temperature and time. It took only 15 min at 140 °C for the complete recovery of Br and I in sediment (GSD‐2) and soil (GSS‐24) reference materials, which is a process that needs 2–6 h at 90 °C. A serious loss of Br and I was found at a higher digestion temperature of 190 °C. A 5% v/v NH₄OH dilution effectively eliminated the memory effects and stabilised the signals of Br and I. Moreover, ammonia dilution also avoided the corrosiveness of HF on the sample introduction system and torch of ICP‐MS. Tellurium is a more suitable internal standard element than In in the ammonia medium. To avoid the adsorption of residues of dissolution on Te, addition of Te should be carried out after centrifuging the solution. The developed method was successfully applied to determine Br and I in fifty‐three Chinese soil and sediment reference materials. This simple method shows great potential for the rapid determination of Br and I in large batches of geological and environmental samples commonly analysed for mineral exploration and environmental geochemistry studies.     

Precise and Accurate Determination of Lu and Hf Contents,and Hf Isotopic Compositions in Chinese Rock Reference Materials by MC‐ICP‐MS

In this contribution, we report Hf isotopic data and Lu and Hf mass fractions for thirteen Chinese rock reference materials (GBW07 103–105, 109–113 and 121–125, that is GSR 1–3, 7–11 and 14–18, respectively) that span a broad compositional range. Powdered samples were spiked with a ¹⁷⁶Lu‐¹⁸⁰Hf enriched tracer and completely digested using conventional HF, HNO₃ and HClO₄ acid dissolution protocols. Fluoride salts were dissolved during a final H₃BO₃ digestion, and chemical purification was performed using a single Ln resin. All measurements were carried out on a MC‐ICP‐MS. This work provides the first comprehensive report of the Lu‐Hf isotopic composition of Chinese geochemical rock reference materials, and results indicate that they are of comparable quality to the well‐characterised and widely used USGS and GSJ rock reference materials.     

Method Development and Optimisation of Sodium Peroxide Sintering for Geological Samples

This work provides a measurement procedure for the complete digestion of rock samples containing refractory minerals such as zircon and chromite. Their dissolution by wet acid digestion is often incomplete but, although providing complete digestions, alkali fusion techniques can result in solutions with a high blank and total dissolved solid content. It was established by the systematic study with reference material trachyandesite MTA‐1 that a 1:6 sample to sodium peroxide (Na₂O₂) ratio is conservative for the complete digestion and recovery of all the analytes especially those contained in zircon. The sample decomposition time was 120 min for the zircon‐bearing rhyolite reference material MRH‐1. Complete digestion of chromite was obtained in the harzburgite RM MUH‐1. The sample solutions were stable for at least 1 year. Accurate measurements of SiO₂, Al₂O₃, TiO₂, P₂O₅ and K₂O could be made with ICP‐MS by not discarding the supernatant of the sinter solution and by using geological reference materials for external calibration. HF digestions are slow, not universal, and may form new mineral/phases that are insoluble under high temperature conditions. The validated sample decomposition procedure combined with ICP‐MS presents an alternative to the use of HF in routine analysis of difficult to digest geological materials.     

High‐precision Determination of Gold Mass Fractions in Geological Reference Materials by Internal Standardisation

Determination of gold abundances in natural rock is critical for applications, but very challenging. Here, we report a method for determining gold with a very low mass fraction (> 0.01 ng g^?1) in rocks. The method involves Carius tube digestion with reverse aqua regia, chromatographic separation to remove most of the sample matrix and measurement by high‐sensitivity ICP‐MS. The mono‐isotopic element gold was quantified by external calibration using an internal standardisation of gold to platinum that was precisely determined by isotope dilution. The method is robust and the obtained results are indistinguishable (< 5–10%, 2s) from those independently obtained by a standard addition technique on the same solution. The results from reference materials TDB‐1 and GPt‐2 are consistent with the certified values and those determined by HF‐aqua regia digestion, confirming the validity of the method. TDB‐1 (n = 20), GPt‐2 (n = 6), BHVO‐2 (n = 9) and other mafic RMs are homogenous for gold (10–20%, 2s) at the 2 g test portion level; however, sample heterogeneity affects some RMs. Gold and platinum‐group elements also display different extents of sample heterogeneity for different RMs. Given the homogeneity observed for TDB‐1, GPt‐2 and BHOV‐2, they are recommended as well‐suited RMs for inter‐laboratory comparison studies of gold.     

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.     

Determination of In and Sn Mass Fractions in Sixteen Geological Reference Materials by Isotope Dilution MC‐ICP‐MS

Mass fractions of Sn and In were determined in sixteen geological reference materials including basaltic/mafic (BCR‐2, BE‐N, BHVO‐1, BHVO‐2, BIR‐1, OKUM, W‐2, WS‐E), ultramafic (DTS‐2b, MUH‐1, PCC‐1, UB‐N) and felsic/sedimentary reference materials (AGV‐2, JA‐1, SdAR‐M2, SdAR‐H1). Extensive digestion and ion exchange separation tests were carried out in order to provide high yields (> 90% for Sn, > 85% for In), low total procedural blanks (~ 1 ng for Sn, < 3 pg for In) and low analytical uncertainties for the elements of interest in a variety of silicate sample matrices. Replicate analyses (n = 2–13) of Sn–In mass fractions gave combined measurement uncertainties (2u) that were generally < 3% and in agreement with literature data, where available. We present the first high‐precision In data for reference materials OKUM (32.1 ± 1.5 ng g^?1), DTS‐2b (2.03 ± 0.25 ng g^?1), MUH‐1 (6.44 ± 0.30 ng g^?1) and PCC‐1 (3.55 ± 0.35 ng g^?1) as well as the first Sn data for MUH‐1 (0.057 ± 0.010 μg g^?1) and DTS‐2b (0.623 ± 0.018 μg g^?1).     

A Method for Rapid Determination of Re and Os Isotope Compositions Using ID‐MC‐ICP‐MS Combined with the Sparging Method

A simple, rapid method for the determination of Re and Os concentrations and isotope compositions using isotope dilution multi‐collector inductively coupled plasma‐mass spectrometry (ID‐MC‐ICP‐MS) combined with Carius tube digestion and sparging introduction of Os was developed. For Os measurement, four channeltron ion counters to detect different Os isotopes were used simultaneously, which led to a drastic reduction in the measurement time. Rhenium isotopes were measured by means of eight Faraday cups with solution nebulisation and an ultrasonic membrane desolvator. The representative ¹⁸⁸Os count rate of an Os standard solution containing 50 pg of total Os was approximately 110000–120000 cps at the onset of measurement; the Re intensity of our in‐house 10 pg g^?1 standard solution reached 1820 V/μg g^?1 with a sample uptake rate of 95–99 μl min^?1. These values indicate that the sensitivity of the method was sufficient even for samples with low Re and Os concentrations, such as chert. As the temporal variations of the amplification efficiency of the ion counters differed from one another, we adopted a sample‐calibrator bracketing method to correct the measured Re and Os isotope ratios. The Re and Os concentrations via the isotope dilution method and the ¹⁸⁷Os/¹⁸⁸Os ratios of two sedimentary rock reference materials (JMS‐2 and JCh‐1) on the basis of the isotope ratios determined by the MC‐ICP‐MS and by negative thermal ionisation mass spectrometry (N‐TIMS) were comparable within their ranges. Based on Os isotope measurement of the IAG reference material [Durham Romil Os (DROsS)], the average difference from the recommended value and precision of Os isotope measurements by the sparging method in combination with multi‐ion‐counters were 0.72% and 0.76% [1RSD (%), n = 29], respectively. The precisions in the ¹⁸⁷Os/¹⁸⁸Os ratios [1RSD (%)] of JMS‐2, JCh‐1 and DROsS were 0.35–0.71, 1.56–3.31 and 0.99–1.28%, respectively, which depended on their Os ion intensities. No systematic difference was observed between the Re and Os geochemical compositions of JCh‐1 and JMS‐2 obtained by means of digestion with inverse aqua regia and CrO₃‐H₂SO₄ solutions, suggesting that either acid solution can be used for the sparging method of sedimentary rock samples. As CrO₃‐H₂SO₄ solution is believed to liberate predominantly the hydrogenous Re and Os fraction from organic‐rich sediment, the sparging method combined with CrO₃‐H₂SO₄ digestion and multi‐ion‐counters in the mass spectrometry is expected to be a powerful tool for reconstructing the secular change in marine Os isotope compositions with high sample throughput.     

镁铁-超镁铁岩铼-锇同位素体系分析方法

通过试验建立了镁铁-超镁铁岩Re-Os同位素体系分析方法，包括Re-Os的化学分离纯化流程，Re同位素比值的电感耦合等离子体质谱测量方法和Os同位素比值的负离子热电离质谱测量方法。化学流程包括Carius管溶样，小型蒸馏分离Os，微蒸馏纯化Os，阴离子交换法分离、纯化Re。用该流程测定了汉诺坝幔源橄榄岩、辉石岩捕虏体和大别山饶拔寨超镁铁岩样品的Re、Os含量和Os同位素比值。     

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.     

Measurements of Rare Earth Element and Other Element Mass Fractions in Environmental Reference Materials (NIST SRM 1646a,NIST SRM 1400, IAEA‐395 and IAEA‐450) by INAA,ICP‐AES and ICP‐MS

INAA, ICP‐AES and ICP‐MS were used to elementally characterise four environmental reference materials – NIST SRM 1646a (Estuarine Sediment), NIST SRM 1400 (Bone Ash), IAEA‐395 (Urban Dust) and IAEA‐450 (Algae). An analytical scheme consisting of the three methods was first applied to NIST SRM 1646a to validate the methodology because it has been extensively analysed and has certified values for many elements. With repeated analyses of NIST SRM 1646a, the accuracy and measurement repeatability of the data obtained were evaluated based on two statistical calculations (zeta‐score and Horwitz ratio) and were observed to be good enough for the analytical scheme to be applied to similar sorts of environmental/geochemical samples. Applying the same approach to NIST SRM 1400, IAEA‐395 and IAEA‐450, enabled mass fractions of 29, 38 and 28 elements to be determined, respectively. Among these results, the data for rare earth elements are of particular interest, not only for IAEA‐450 but also for the other three reference samples. The data for Pr, Gd, Dy, Ho, Er and Tm in NIST SRM 1646a are newly reported in this study. By using small test portions (< 100 mg) for NIST SRM 1646a and IAEA‐395, and recommended minimum amounts for NIST SRM 1400 and IAEA‐450, sample homogeneity was evaluated.     

Determination of Platinum‐Group Elements and Gold in Ferromanganese Nodule Reference Samples

A measurement procedure for determining of Ru, Pd, Ir, Pt and Au mass fractions in ferromanganese deposits by inductively coupled plasma‐mass spectrometry after acid digestion and anion exchange preconcentration is presented. To eliminate incomplete recovery after sorption preconcentration of the platinum‐group elements (PGE) and Au, a standard addition method was used. Detection limits ranged from 0.02 ng (Pd, Ir) to 0.19 ng (Ru). The measurement results for ferromanganese nodule reference material NOD‐A‐1 and NOD‐P‐1 agree with earlier reported values. Intermediate precision of PGE concentration data for nodule reference materials in this work was 5–24% (1s) and could reflect sample heterogeneity.