Isotope Dilution with Matrix Element Removal: A Key for High-Precision, High-Accuracy Trace Analysis of Geological Samples Using Inductively Coupled Plasma-Mass Spectrometry

The isotope dilution (ID) method requires only the measurement of mass and isotopic mass ratios. For this reason, ID is considered a primary method of analysis, capable of higher precision and accuracy than comparative methods used in conventional instrumental analysis, that are based on calibration relative to reference materials. Compared to thermal ionisation mass spectrometers, inductively coupled plasma source-mass spectrometers (ICP-MS) benefit from several practical advantages, including direct liquid sampling at atmospheric pressure, a multi-element capability, high ionisation efficiency, fast scanning capability and widespread availability. These features greatly improve sample throughput, thereby allowing the isotope dilution method to be used on a routine basis. In turn, ID alleviates the need for quantitative sample handling, and thus makes separation of the analytes from matrix elements much easier. This allows ICP-MS instruments to be used under optimal conditions, because it is possible to use advanced, high efficiency sample introduction systems without resorting to large dilution factors. Moreover, the cleanliness of the sampling interface and ion optics is preserved, thereby allowing optimum instrumental performance to be maintained for extended periods, so reducing maintenance costs. Examples are given in this review to highlight the potential of isotope dilution combined with analyte separation for achieving high precision in trace element analysis of geochemical samples.     

Determination of Trace Elements in Twenty Six Chinese Geochemistry Reference Materials by Inductively Coupled Plasma-Mass Spectrometry

We report new data for thirty seven elements determined in twenty six Chinese geochemistry reference materials using inductively coupled plasma-mass spectrometry and a reliable and simple dissolution technique. One hundred milligrams of sample were digested with 1 ml of HF and 0.5 ml of HNO₃ in PTFE-lined stainless steel bombs heated to 200 °C for 12 hours. Insoluble residues were dissolved using 6 ml of 40% v/v HNO₃ heated to 140 C for 3 hours. Analytical calibration was accomplished using aqueous standard solutions. Rhodium was used as an internal standard to correct for matrix effects and instrument drift. Precisions were typically better than 5% RSD. Most of the data presented here agree well with the published certified values. For the elements Zr, Hf and most other trace elements, the measured values were less than 10% in error when compared to certified values.     

Isotopic and Elemental Imaging of Geological Materials by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry

Laser ablation ICP-MS represents a promising new development for the acquisition of elemental and isotopic images from a variety of different materials. Compared to existing methods for imaging, it offers relatively rapid throughput, very wide dynamic range, a relatively clean mass spectrum, utility at a variety of scales (from μm to cm) and multi-element/isotopic capability. Although developing rapidly in the biological sciences, the method has not yet seen widespread application to geological materials. This contribution documents some preliminary experiments aimed at understanding the fundamental aspects of elemental and isotopic image acquisition using laser ablation ICP-MS. In particular, we note that ablation cell designs must be optimised to promote rapid system response, in contrast to the signal-smoothing that is often preferred for simple spot analyses. Furthermore, experimental parameters must be carefully evaluated on a system-by-system basis to avoid the blurring effects of re-sampling phenomena. With careful attention to these details, and development of appropriate data processing software, laser ablation ICP-MS imaging has much to offer workers in the Earth and environmental sciences.     

Boron Determination in Twenty One Silicate Rock Reference Materials by Isotope Dilution ICP-MS

The concentration of boron was determined in twenty one geochemical reference materials (silicate rocks) by isotope dilution inductively coupled plasma-mass spectrometry. Boron was extracted from the rocks using HF digestion, suppressing boron volatilisation through boron-mannitol complexation. Sample solutions, in a diluted HCl matrix, were analysed by ICP-MS without any separation of boron from the matrix elements. The results obtained were in agreement with the literature data and indicate that using the described procedure, trace amounts of boron can be very easily determined in complex matrices with rapidity and precision. With the instrumentation and reagents used in this study, this procedure can be used for the determination of 0.5 μg g⁻¹ boron in a 15 0 mg silicate rock sample. Replicate analyses of the twenty one geochemical reference materials (GRM), ranging in boron concentration from 1.35 to 15 7 μg g⁻¹, yielded precisions (relative standard deviation) varying between 0.9 and 9.8%.     

高分辨电感耦合等离子体质谱法测定地球化学样品中钪钇和稀土元素

建立了高分辨电感耦合等离子体质谱法(HR-ICP-MS)测定地球化学样品中钪、钇、镧、铈、镨、钕、钐、铕、钆、铽、镝、钬、铒、铥、镱和镥的分析方法。样品经氢氟酸-硝酸-硫酸-王水消解,试液直接用HR-ICP-MS测定钪、钇和14种稀土元素。用高分辨模式有效地避免了多原子离子及难熔氧化物离子对待测元素测定的干扰,为钪、钇和14种稀土元素选择了最佳的测定同位素和合适的分辨率;用地球化学标准物质制备的溶液优化仪器工作参数,确定了最佳的仪器测定条件。方法检出限(6σ)为0.003～0.013μg/g(稀释因子为1000),相对标准偏差(RSD,n=12)小于6%。方法经国家一级地球化学标准物质验证,测定值与标准值吻合。     

Determination of Scandium, Yttrium and Rare Earth Elements in Rocks by High Resolution Inductively Coupled Plasma-Mass Spectrometry

The high sensitivity, minimal oxide formation and single internal standard capability of high resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS) is demonstrated in the direct determination of Sc, Y and REE in the international reference materials: basalts (BCR-1, BHVO-1, BIR-1, DNC-1), andesite (AGV-1) andultramafics (UB-N, PCC-1 and DTS-1). Time consuming ion exchange separation or preconcentration were found to be unnecessary. Smooth chondrite normalized plots of the REE in PCC-1 and DTS-1 were obtained in the range 0.8-50 ng g-1 (0.01-0.1x chondrite). Method precision was found to be digestion dependent with an average external repeatability of 2-4% for the basalts, AGV-1 and UB-N, and 10% for PCC-1 and DTS-1. The mass peak due to ⁴⁵Sc was completely resolved from ²⁹Si¹⁶O and ²⁸Si¹⁶O¹H spectral interferences using medium resolution, which casts doubt on the accuracy of Sc determinations using quadrupole ICP-MS. Literature values for Y in rock reference materials were found to be approximately 9% high after HR-ICP-MS and XRF analysis.     

Multi-Element Isotope Dilution Sector Field ICP-MS: A Precise Technique for the Analysis of Geological Materials and its Application to Geological Reference Materials

We present a multi-element technique for the simultaneous determination of twelve trace elements in geological materials by combined isotope dilution (ID) sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) following simple sample digestion. In addition, the concentrations of fourteen other trace elements have been obtained using the ID determined elements as internal standards. This method combines the advantages of ID (high precision and accuracy) with those of SF-ICP-MS (multi-element capability, fast sample processing without element separation) and overcomes the most prevailing drawbacks of ICP-MS (matrix effects and drift in sensitivity). Trace element concentration data for BHVO-1 (n = 5) reproduced to within 1–3% RSD with an accuracy of 1–2% relative to respective literature values for ID values and 2–3% for all other values. We have applied this technique to the analysis of seventeen geological reference materials from the USGS, GSJ and IAG. The sample set also included the new USGS reference glasses BCR-2G, BHVO-2G and BIR-1G, as well as the MPI-DING reference glasses KL2-G and ML3B-G, and NIST SRM 612. Most data agreed within 3–4% with respective literature data. The concentration data for the USGS reference glasses agreed in most cases with respective data of the original rock powder within the combined standard uncertainty of the method (2–3%), except the U concentration of BIR-1G, which showed a three times higher concentration compared to BIR-1.     

Determination of Chlorine in Nine Rock Reference Materials by Isotope Dilution Mass Spectrometry

A procedure for the determination of chlorine by the isotope dilution technique (ID) using negative thermal ionisation mass spectrometry (N-TIMS) is described. Silicate samples of about 10 mg were spiked and decomposed with hydrofluoric acid, and chlorine was isolated by precipitation of silver chloride after neutralisation with Ca(OH)₂. The ammonical solution of AgCl was then subjected to N-TIMS. Replicate analyses of rock reference materials, typically of JB-1 and JR-1, demonstrated the high quality of the analyses (precision for Cl was ± 1-2%). We present here the most precise data sets of chlorine concentrations in nine igneous rock reference materials, three basalts (JB-1, JB-2, JB-3), two andesites (JA-3, AGV-1), two rhyolites (JR-1, JR-2) and two granodiorites (JG-3, GSP-1). The chlorine concentrations found ranged from 152 μg g-1 in AGV-1 to 1008 μg g^-1 in JR-1. Our results presented here are partly (but not completely) in agreement with recommended values, where they are available. The N-TIMS ID technique can thus be used as a means of determining low chlorine contents in silicate materials to high precision.     

电感耦合等离子体质谱法测定地质样品中铜锌铕钆铽的干扰及校正

由于电感耦合等离子体质谱(ICP-MS)分析不是在封闭的真空系统中进行,在测定过程中,气体、水和酸产生的一些离子都可能进入检测系统,产生干扰,严重影响痕量元素的准确分析。文章采用氢氟酸-硝酸封闭压力酸溶分解样品,ICP-MS法同时测定地质样品中Cu、Zn、Eu、Gd、Tb,研究了Ti、Ba、Ce、Pr、Nd对Cu、Zn、Eu、Gd、Tb的干扰情况。实验选择质量数65Cu、66Zn、153Eu、157Gd、159Tb作为测定同位素,用干扰系数脱机校正法校正分别来自Ti、Ba、Ce、Pr、Nd的氧化物重叠干扰,有效地解决了被干扰元素在测定时数值准确度低的问题。方法检出限(稀释因子1000)为:Cu 0.47μg/g、Zn 0.82μg/g、Eu 0.002μg/g、Gd 0.004μg/g、Tb 0.002μg/g,方法精密度(RSD,n=12)<5%,准确度(RE)<5%。方法用岩石、土壤、水系沉积物国家一级标准物质进行验证,测定值与标准值相符,适用于地质样品中Cu、Zn、Eu、Gd、Tb的测定。     

高分辨电感耦合等离子体质谱法测定地球化学样品中的 36种元素

土壤和水系沉积物地球化学样品经氢氟酸-硝酸-高氯酸敞开酸溶消解,王水提取,试液直接用高分辨率电感耦合等离子体质谱法(HR-ICP-MS)同时测定其中的Li、Be、P、Sc、Ti、V、Cr、Mn、Co、Ni、Cu、Zn、Ga、Rb、Sr、Nb、Mo、Cd、In、Sb、Cs、Ba、Hf、Ta、W、Tl、Pb、Bi、Th、U、Na2O、MgO、Al2O3、K2O、CaO、TFe2O3等36种组分。对各元素的测定同位素及分辨率进行优选,有效消除了绝大多数多原子及双电荷离子干扰的影响。痕量元素的方法检出限(6σ)在0.002～2.031μg/g之间,主量元素的检出限(6σ)在10.0～100μg/g之间(稀释因子=1000),所有元素的相对标准偏差(RSD,n=12)均小于10%。方法经国家一级地球化学标准物质验证,测定值与标准值吻合。     

同位素稀释等离子体质谱法准确测定地质样品中痕量铼

采用Carius管高温密闭溶样,同位素稀释-电感耦合等离子体质谱法对黄铁矿、岩石等地质样品中痕量铼进行了准确测定。流程空白能够有效控制在1．4～10 pg。对岩石样品中 ng／g量级的Re进行分析,4次重复分析结果的RSD为3．89％(2s)。以辉钼矿国家标准物质作为本方法研究的监控样品,重复分析结果与其标准推荐值(17．39±0．32)μg/g吻合。     

Determination of the Platinum-Group Elements and Gold in Twenty Rock Reference Materials by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) after Pre-Concentration by Nickel Sulfide Fire Assay

The platinum-group elements (PGE) and gold have been determined in twenty international rock reference materials by inductively coupled plasma-mass spectrometry (ICP-MS) after pre-concentration by a nickel sulfide fire assay. It was possible to achieve determination limits for a 50 g sample that ranged from 1 pg g^-1 (Rh) to 23 pg g^-1 (Au). Compared to published certified and recommended values for rock reference materials, the trueness of the method was found to be good. However, in some cases we observed large deviations for all elements in the sub 10 ng g^-1 range within individual reference sample splits. Our results show that the PGE and Au are inhomogeneously distributed in the reference materials analysed here, where they are present in low concentrations, using 50 g test portions.     

High Precision Ru, Pd, Ir, Pt, Re and REE Determinations in the Stevns Klint Cretaceous-Tertiary Boundary Reference Material (FC-1) by Isotope Dilution Multiple Collector Inductively Coupled Plasma-Mass Spectrometry

We present high precision Ir, Ru, Pt, Pd, Re and rare earth element (REE) determinations by isotope dilution multiple collector-ICP-MS on the Cretaceous-Tertiary boundary sedimentary reference material FC-1. Samples for platinum-group element measurements were digested in Carius tubes followed by acid digestion. The platinum-group elements were subsequently separated by anion exchange chemistry and determined by multiple collector-ICP-MS. The accuracy of the platinum-group element analyses have been verified by comparative analyses of the reference materials WITS-1 and GP13 (sample size 0.5-1 g). Replicate analyses of FC-1 (sample size 0.2 g) exhibit good reproducibility (RSD < 5%) for all the analysed platinum-group elements. REE data also exhibit excellent reproducibility (RSD < 0.5%), which indicates that this sample is homogeneous for the determination of the platinum-group elements and REE at the 0.2 g level.     

Basaltic and Solution Reference Materials for Iron,Copper and Zinc Isotope Measurements

Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS‐Fe, CAGS‐Cu and CAGS‐Zn) and one basalt (CAGS‐Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter‐laboratory analytical comparisons involving up to eight participating laboratories employing MC‐ICP‐MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM‐014 for Fe, NIST SRM 976 for Cu and IRMM‐3702 for Zn. Respective reference values of CAGS‐Fe, CAGS‐Cu and CAGS‐Zn solutions are as follows: δ⁵⁶Fe = 0.83 ± 0.07 and δ⁵⁷Fe = 1.20 ± 0.13, δ⁶⁵Cu = 0.57 ± 0.06, and δ⁶⁶Zn = ?0.79 ± 0.12 and δ⁶⁸Zn = ?1.65 ± 0.24, respectively. Those of CAGS‐Basalt are δ⁵⁶Fe = 0.15 ± 0.07, δ⁵⁷Fe = 0.22 ± 0.10, δ⁶⁵Cu = 0.12 ± 0.08, δ⁶⁶Zn = 0.17 ± 0.13, and δ⁶⁸Zn = 0.34 ± 0.26 (2s).     

封闭酸溶-等离子体质谱法分析超细粒度地质样品中42个元素

采用封闭压力酸溶,电感耦合等离子体质谱法（ICP—MS）测定了超细样品的42个元素,研究了样品的粒度、分解条件、取样量对分析准确度和精密度的影响。结果表明,用超细粉碎样品（〈30μm）,取样量减小至2mg仍能保证取样代表性,总用酸量可减至0．5mL,反应时间也可大大缩短。采用超细样品可更好地发挥ICP—MS技术高灵敏度的效能,从而达到保护环境、降低分析成本、提高分析效率的目的。     

Molybdenum Concentrations Measured in Eleven USGS Geochemical Reference Materials by Isotope Dilution Thermal Ionisation Mass Spectrometry

Molybdenum concentrations in eleven USGS geochemical reference materials AGV-1, BCR-1, BHVO-1, BIR-1, DNC-1, DTS-1, G-2, GSP-1, MAG-1, PCC-1 and W-2 were measured by isotope dilution thermal ionisation mass spectrometry (ID-TIMS). In every case but one, the concentrations determined in this study were significantly lower than the current consensus values. Molybdenum concentrations determined by ID-TIMS are inherently more accurate and precisions may be up to an order of magnitude higher than those measured by other analytical techniques.     

感耦等离子体质谱法同时测定岩石中痕量元素的研究

试验了含难熔组分的岩石样品的分解方法、熔剂用量，以及溶液中可溶盐量的控制和标准系列的熔剂匹配等问题；分别采用Ｒｅ、Ｒｈ和Ｉｎ作内标，解决了基体效应及其基体导致的灵敏度漂移的影响，实现了不经分离富集直接用ＩＣＰ－ＭＳ法测定岩石样品中３４个痕量元素。方法测定限０．０１～５μｇ／ｇ，ＲＳＤ（ｎ＝１０）为２．６％～１３％，已应用于地质试样分析，岩石标样分析结果与标准值相符。     

电感耦合等离子体质谱法精确测定地质样品中的微量元素镓

应用电感耦合等离子体质谱法(ICP-MS)对地质样品中微量元素镓进行测试分析时,存在两方面问题:一是不同消解方法各有不足,密闭式消解不能批量处理样品,而敞开式消解过程繁杂;二是质谱测试时需要选择⁶⁹Ga还是⁷¹Ga,确定扣除哪些干扰和相应的扣除系数,这些因素使地质样品中镓元素的测试精度不高。本文基于一般地质样品中有机质含量低的特点,针对ICP-MS分析方法提出:①使用氢氟酸、盐酸、硝酸、高氯酸四种酸混合消解样品,采用半密闭式酸分解法,通过调整加热温度、用酸量、用酸比等加快反应进程,少量的有机质在强酸加热消解时能够反应完全,而不必要进行灰化处理;②采用丰度为39.9%的⁷¹Ga进行测试,使用经验系数0.005,利用⁵⁵Mn¹⁸O对⁷¹Ga位置扣除⁵⁵Mn¹⁶O的干扰。方法精密度在3%以内,方法检出限为0.06 μg/g。本方法简化了样品消解过程,并可批量处理样品,降低了分析成本,在准确测定镓元素的同时还能理想地测定其他微量元素和稀土元素。     

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).