MC-ICP-MS高精度测定Pb同位素比值

多接收器等离子体质谱是近年发展起来的高精度同位素分析手段之一，通过用等离子体质谱测量Pb国际标准物质NBS981和NBS982,显示出多接收器等离子体质谱分析Pb同位素的优势。利用205Tl/203Tl进行作为内标，可以实现Pb同位素的质量分馏校正，极大地提高了Pb同位素分析的重现性。相比较热电离质谱，该方法精度更高，样品的用量更少，测试时间更短，多接收器等离子体质谱测定Pb同位素技术有良好的应用前景。     

通用同位素标准化程序及在Sr、Nd同位素分析上的应用

固体元素的同位素在热表面电离质谱计上分析时,会产生同位素分馏,使得同位素比值测量的重复性和测量精度都受到局限。而在同位素地质学中,有时所遇到的样品之间的同位素比值差别很小,以致被测量过程中的同位素分馏所掩盖,使同位素地质方法的应用受到限制。     

稳定同位素质谱与同位素光谱结合的方法分析氧同位素17O/16O

传统的氧同位素分析方法一般将各种形式的氧转化为CO2,再通过稳定同位素质谱测定其氧同位素组成,由于二氧化碳中的17O和13C在质谱中有相同的质荷比m/z,这种方法不能测得17O同位素的丰度,三氧同位素(16O、17O、18O)丰度分析的关键是17O同位素丰度的分析.为了测量17O同位素丰度,一般需要先将各种形式的氧转化为O2,然后利用稳定同位素质谱进行分析,转化过程复杂或者有危险.本文提出了一种新思路,应用稳定同位素质谱与碳同位素光谱相结合的方法分析17O/16O.先采用传统方法将各种形式的氧转化为CO2,再由多接收器稳定同位素质谱计测得CO2的质谱峰高比45/44(记为R45),同位素光谱如光腔衰荡光谱测得13C/12C(定义为R13),计算其同位素比值17O/16O=(R45-R13)/2,方法的分析精度好于±0.08‰(1σ).该方法是在传统方法的基础上,增加一个CO2碳同位素光谱分析步骤,通过简单的数据处理就可以获得17O同位素组成,而无需将各种形式的氧转化为O2,18O同位素样品制备方法成熟,无危险性,且分析精度优于或相当于其他测试方法.     

激光探针等离子体质谱用于锆石Pb-Pb定年的分析和校正方法的进一步探讨

激光探针等离子体质谱可对锆石进行快速准确的Ｐｂ－Ｐｂ同位素定年。本文进一步探讨了该方法应用中的几个问题。对不同样品采用不同的聚焦方式可以对Ｕ／Ｐｂ分异有一定的控制作用。在一定的条件下,不连续和连续采样模式都可以得到较高精度和准确度的结果。连续采样模式还可以得到同位素计数的深度剖面。不同的测量滞留时间会影响测量结果的精度。２０ｍｓ为适合锆石２０７Ｐｂ／２０８Ｐｂ分析的最佳测量滞留时间。在对测定结果进行校正时,可以采用玻璃标样ＮＩＳＴ６１０和钻石标样两种不同的校正方法。     

多接收器等离子体质谱(MC-ICPMS)高精度测定Nd同位素方法

多接收器等离子体质谱是近年发展起来的高精度同位素分析手段之一,通过用等离子体质谱测量Nd国际标准材料La Jolla和JMC Nd203以及实际样品GBW04419,研究MC-ICPMS测量Nd的质量分馏特点,解决MC-ICPMS测量的关键所在质量分馏校正.通过修正分馏系数,可以实现理想的分馏校正.结果显示出所得到的分析精度达到热电离质谱的测量水平.具有实际地质样品代表性的实验室内部标准CAGS-Nd-1重现性长期分析结果为:143Nd/144Nd=0.512072±0.000008(2σ,n=140).     

低质量数元素同位素在线连续流同位素比值质谱分析的质量控制和数据标准化

同位素比值质谱分析方法是准确测量各种同位素相对丰度的标准方法。连续流同位素质谱的出现不仅提高运行效率,也降低了样品用量并提高灵敏度。但是,要使这种方法获得更好准确度和精度的同位素数据,并做到所获得数据可与其他实验室结果进行类比,从而得到可靠的同位素数据,这就需要好的分析策略和运行方案,还需要对仪器日常性能和数据质量进行严密的监视管控,而且还取决于原始数据如何进一步标准化到国际同位素尺度上。因此,同位素比值质谱结合元素分析仪(或热转换元素分析仪)连续流方法要实现可靠的稳定同位素分析需要:①设备安装和环境控制、测试准备、样品制备和称量、标准物质选择及序列等规范化质量控制措施;②严格校准仪器系统(包括调节灵敏度和线性,背景值监测,稳定性检测,H+3系数校正等);③可靠的数据处理。目前不同的实验室,采用标准物质来标定系统、对测量的同位素数据进行标准化,以及利用控制曲线来监测系统稳定性并对不确定度的计算,这些策略往往都不同。因此,统一的数据处理方案是被高度期待的。目前最好的执行方案是基于线性回归的两点或多点标准化方法。如果每一批样品中测量两个不同的标准物质四次,或者测量四个标准物质两次,那么不确定度会降低50%。当前同位素比值质谱能够测定同位素比值的不确定度一般要好于0.02‰。但是,标准物质的使用既要考虑样品的性质,同时要涵盖它们未知同位素组成的范围,尤其氢同位素在现阶段缺乏标准物质和测量的仪器精度较差(比碳、氮、氧等要低一个数量级)的情况下,这显然是稳定同位素分析者的一个重大挑战。本文概括了同位素比值质谱结合元素分析仪(或热转换元素分析仪)的基本操作原理和分析实践,将数据处理运用到同位素比值分析之中,获得连续流同位素比值质谱分析结果的合理准确度和精度。     

多接收器等离子体质谱精确测定铼含量及其同位素丰度

利用多接收器等离子体质谱建立了快速精确测定铼含量及其同位素丰度的方法。溶液中加入铱元素进行铼同位素的质量分馏校正,在常规的溶液雾化进样条件下,采用同位素稀释法可准确测定纳克级的铼含量。铼标样A的自然同位素丰度的测量结果为185Re(37.437±0.008)%、187Re(62.563±0.008)%(2σ,n=5);铼稀释剂的同位素丰度测量结果为185Re(5.576±0.018)%、187Re(94.424±0.018)%(2σ,n=7);与未进行分馏校正的同位素组成的测量结果相比,精度和准确度均有提高。利用同位素稀释法测得铼标样A的浓度为(516.48±0.35)ng/g(2σ,n=5);测量精度和准确度均优于0.10%;利用反同位素稀释法对铼稀释剂B进行了详细的测量,平均测量结果为(62.74±0.26)ng/g(2σ,n=15),在分析误差范围内与其标定值完全一致;与未进行分馏校正的浓度测量结果相比,铼同位素丰度及铼含量的测量准确度均明显提高。     

在线加标-电感耦合等离子体质谱法测量纯钼中痕量杂质元素

纯钼的纯度或杂质含量对材料性能有重要的影响，痕量杂质的准确测量是产品质量控制的关键。电感耦合等离子体质谱法(ICP-MS)由于具有高灵敏、多元素同时测量的优势，是测量痕量杂质的最有效方法之一；但在测量高浓度纯钼基体中的痕量杂质时，会产生较强的基体抑制效应，严重影响测量结果准确性。基体匹配法、标准加入法以及基于同位素丰度比值测量的同位素稀释质谱法(IDMS)可以有效地补偿复杂的基体效应，获得准确的测量结果；但步骤繁琐、分析效率低、分析成本高使其难以满足高通量的测量需求。本万工作集成了标准加入法的准确性及在线自动分析的高效性，基于标准加入法的原理，通过双路进样，将样品溶液与标准溶液(系列标准溶液依次自动进样)同时引入三通进行混合，然后经过雾化进入ICP-MS进行检测，从而建立了基于在线加标的ICP-MS法。该方法有效地补偿了高浓度试样的基体效应，通过样品-标准进样流量差异的校正，提高了测量结果的准确性，实现了纯钼中29种痕量杂质元素的快速准确测量，满足了纯钼中痕量杂质标准物质的准确定值要求。经考察，本工作建立的方法对29种元素的方法检出限(MDL)在0.004～0.90μg/g之间，标准加...     

高精度质谱计在同位素地球化学的应用前景

微量地质样品的高精度同位素比值测试已经成为地质和环境科学等领域极其重要的研究手段.新型固体热电离质谱计以其高精度和高灵敏度, 将在同位素年代学和地球化学领域有广阔的应用前景.报道采用IsoProbeT质谱计测量标准物质溶液的结果.测量锶标准物质NBS987和钕标准物质Ames分别获得平均87Sr/86Sr比值0.710 241 8±0.000 005 1和平均143Nd/144Nd比值0.512 148 4±0.000 002 9, 内部精度可达0.000 3%.微量锶标准物质(0.3~1 ng) 的同位素比值测量内部精度可以优于0.003%.结合低本底化学流程, 实现了微量地质样品的高精度同位素比值测试.这一结合将有效地促进单颗粒矿物年代学和同位素示踪在岩浆岩、变质岩、矿床、构造岩研究的应用.      

(LP)MCICPMS方法精确测定液体和固体样品的Sr同位素组成

MCICPMS是近年发展起来的高精度固体同位素分析仪器,利用MCICPMS可以精确测定Sr同位素组成,与TIMS相比,分析效率明显提高;对于含有Rb的实际样品,在Rb/Sr比值较小时(Rb/Sr<0.001),可以通过Rb扣除获得准确的87Sr/86Sr比值,而当Rb含量较高时,可以通过建立Rb/Sr与87Sr/86Sr偏差值的线性关系进行再一次校正,同样也可以获得准确的87Sr/86Sr比值.通过这种校正关系,可以直接分析固体微区的Sr同位素组成.     

Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS

We have developed a technique for the accurate and precise determination of ³⁴S/³²S isotope ratios (δ³⁴S) in sulfur-bearing minerals using solution and laser ablation multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). We have examined and determined rigorous corrections for analytical difficulties such as instrumental mass bias, unresolved isobaric interferences, blanks, and laser ablation- and matrix-induced isotopic fractionation. Use of high resolution sector-field mass spectrometry removes major isobaric interferences from O₂⁺. Standard-sample bracketing is used to correct for the instrumental mass bias of unknown samples. Background on sulfur masses arising from memory effects and residual oxygen-tailing are typically minor (< 0.2‰, within analytical error), and are mathematically removed by on-peak zero subtraction and by bracketing of samples with standards determined at the same signal intensity (within 20%). Matrix effects are significant (up to 0.7‰) for matrix compositions relevant to many natural sulfur-bearing minerals. For solution analysis, sulfur isotope compositions are best determined using purified (matrix-clean) sulfur standards and sample solutions using the chemical purification protocol we present. For in situ analysis, where the complex matrix cannot be removed prior to analysis, appropriately matrix-matching standards and samples removes matrix artifacts and yields sulfur isotope ratios consistent with conventional techniques using matrix-clean analytes. Our method enables solid samples to be calibrated against aqueous standards; a consideration that is important when certified, isotopically-homogeneous and appropriately matrix-matched solid standards do not exist. Further, bulk and in situ analyses can be performed interchangeably in a single analytical session because the instrumental setup is identical for both. We validated the robustness of our analytical method through multiple isotope analyses of a range of reference materials and have compared these with isotope ratios determined using independent techniques. Long-term reproducibility of S isotope compositions is typically 0.20‰ and 0.45‰ (2σ) for solution and laser analysis, respectively. Our method affords the opportunity to make accurate and relatively precise S isotope measurement for a wide range of sulfur-bearing materials, and is particularly appropriate for geologic samples with complex matrix and for which high-resolution in situ analysis is critical.     

流体包裹体的喇曼光谱分析进展

激光显微喇曼光谱已经成为流体包裹体非破坏性分析的重要手段。它可以快速方便地对单个包裹体进行定性、半定量乃至定量分析，且样品制备简单。通过对入射光进行聚焦，可以分析样品中微米级的包裹体。激光显微喇曼光谱对纯气相包裹体、盐水溶液包裹体、含挥发分的水溶液包裹体，以及有机包裹体的分析已经显示出了很大的潜力。此外，对流体包裹体中同位素比值的分析和作为高温高压下流体的分子之间作用的研究也具有很大应用前景。     

Evaluation of Simultaneous Analyte Leaching/Vapour Phase Introduction for Direct Osmium Isotope Ratio Measurements in Solid Samples by Double-Focusing Sector Field ICP-MS

The analytical performance of a method for Os isotope ratio measurement by double‐focusing, sector field ICP‐MS (ICP‐SFMS) was evaluated. The method is based on several optimised, concurrent processes: Os extraction from samples in hot concentrated nitric acid; separation of Os from the digest solution by the formation of volatile osmium tetroxide accelerated by continuous hydrogen peroxide addition; transport of analyte vapour by an oxygen flow into the ICP; and isotopic determination by ICP‐SFMS. Due to the very efficient utilisation of analyte (approaching 0.5‰), Os isotope ratio measurement could be performed at low pg levels. Combined with an ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub pg g^?1 range could be determined by this method. Given that two complete digestion/distillation systems were available for interchangeable use, throughputs of up to fifteen samples per 8 hour shift could be achieved. The method precision, evaluated as the long‐term reproducibility of ¹⁸⁷ Os/¹⁸⁸Os ratio measurements in a commercial Os reference sample containing 0.5 ng Os, was 0.16% relative standard deviation (RSD, 1s). The method has been applied to perform replicate ¹⁸⁷ Os/¹⁸⁸ Os ratio measurements on a suite of fifty reference materials of various origins and matrix compositions, with Os concentrations varying from < 0.1 pg g^?1 to > 100 ng g^?1, yielding an average precision of 3% RSD. Though none of the materials tested are certified for Os content or Os isotope composition, comparison of the obtained data with published Os isotope information for similar sample types revealed close agreement between the two. The method can also be used for the simultaneous, semi‐quantitative determination of Os concentrations.     

Comparison of Pb Purification by Anion-Exchange Resin Methods and Assessment of Long-Term Reproducibility of Th/U/Pb Ratio Measurements by Quadrupole ICP-MS

A comparison between HBr-HCl and HBr-HNO₃ based anion chemistry is presented to test the efficiency of Pb purification in the preparation of samples for isotope ratio measurement by ICP-MS. It was found that the small advantages in yield and blank offered by the HNO₃-based method were more than compensated by the more effective matrix removal of the HCl-based method. Apart from very zinc rich matrices (e.g., sphalerite), a careful single pass purification using HBr and HCl removed more than 99.9% of the matrix. In preparation for the isotope ratio analysis, a small (2–5% m/v) liquid sample aliquot was analysed to determine U, Th and Pb concentrations by solution quadrupole ICP-MS. This allowed accurate prediction of the expected ion signal and permitted optimal spiking with Tl, if desired, for mass bias correction. Long-term results for international rock reference materials showed reproducibilities of better than 1% (Th/U) and 1.5% (U/Pb). For most geological applications, such analyses obviate the need for isotope dilution concentration measurements.     

Trace Element Data on Geostandards by Mass Spectrometric Isotope Dilution Technique

The stable isotope dilution technique using solid source mass spectrometry is described. The method is capable of high sensitivity, and can yield accurate determinations of elements in trace quantities. The method enjoys freedom from interference effects and systematic errors, and because of its high absolute accuracy it is ideal for the determination of trace elements in geochemical reference samples. A compilation of isotope dilution analyses on ten trace elements in a number of international standard rock samples carried out at the Western Australian Institute of Technology is presented.     

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.     

High‐Precision Mass‐Dependent Molybdenum Isotope Variations in Magmatic Rocks Determined by Double‐Spike MC‐ICP‐MS

Small mass‐dependent variations of molybdenum isotope ratios in oceanic and island arc rocks are expected as a result of recycling altered oceanic crust and sediments into the mantle at convergent plate margins over geological timescales. However, the determination of molybdenum isotope data precise and accurate enough to identify these subtle isotopic differences remains challenging. Large sample sizes – in excess of 200 mg – need to be chemically processed to isolate enough molybdenum in order to allow sufficiently high‐precision isotope analyses using double‐spike MC‐ICP‐MS techniques. Established methods are either unable to process such large amounts of silicate material or require several distinct chemical processing steps, making the analyses very time‐consuming. Here, we present a new and efficient single‐pass chromatographic exchange technique for the chemical isolation of molybdenum from silicate and metal matrices. To test our new method, we analysed USGS reference materials BHVO‐2 and BIR‐1. Our new data are consistent with those derived from more involved and time‐consuming methods for these two reference materials previously published. We also provide the first molybdenum isotope data for USGS reference materials AGV‐2, the GSJ reference material JB‐2 as well as metal NIST SRM 361.     

Isotope Ratio Determination in the Earth and Environmental Sciences: Developments and Applications in 2003

This annual review documents developments and applications in the field of isotope ratio determination, as reflected in the literature for the Earth and environmental sciences for the year 2003. Particular emphasis is placed upon the relationship between the two dominant analytical techniques-thermal ionisation mass spectrometry (TIMS) and multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS)-and the rapidly changing nature of their roles in isotope analysis. Additionally, the review covers developments in single-collector ICP-MS and TOF technologies, new sample preparation procedures and the characterisation of isotopic reference materials, together with fundamental investigations of mass spectrometer performance.     

Formation Depth Estimation of Coesite-Bearing Eclogite in Dabie UHPM Zone, China： Constrained by Isotopic Studies

The formation depth of metamorphic rocks in the Dabie ultrahigh pressure metamorphic (UHPM) zone influences not only our understanding of formation mechanism and evolution processes of collision orogenic belt, but also the studies on earth's interior and geodynamic processes. In this study, the isotopic data of metamorphic rocks in the Dabie UHPM zone are discussed to give constraints on the formation depth in the Dabie UHPM zone. The εSr of eclogite in the Dabie UHPM zone varies from 18 to 42, and the εNd varies from -6.1 to -17, both of them show the characters of isotopic disequilibrium. The oxygen isotope studies indicate that the protoliths of these UHPM rocks have experienced oxygen isotope exchange with meteoric water (or sea water) before metamorphism and no significant changes in the processes of metamorphism on their oxygen isotope composition have been recorded in these rocks. Except for one sample from Bixiling, all samples of eclogite from Dabie UHPM zone show the 3He/4He ratios from 0.79×10-7 to 9.35×10-7, indicating the important contribution of He from continental crust. All Sr, Nd, O and He isotopic studies indicate that the UHPM rocks retain the isotopic characteristics of their protoliths of crust origin. No significant influence of mantle materials has been found in these metamorphic rocks. Trying to explain above isotopic characteristics, some researchers assume that the speeds of dipping thrust and uplifting of rocks were both very high. In this condition, there will not be enough time for isotopic exchange between crust protolith and mantle materials. Therefore, we can not see the tracer of mantle materials in these UHPM rocks. However, this assumption can not be justified with available knowledge. Firstly, it was estimated that the whole process of UHPM took at least 15 Ma. During such a long period, and at the metamorphic temperature of ≥700 ℃, the protolith of crust origin can not escape from isotopic exchange with mantle materials if the UHPM have happened in the mantle depth of ≥100 km. In contrast, all problems will be dismissed if we assume that the UHPM have happened at the depth still in crust.     

Obtaining Accurate Isotopic Compositions with the Double Spike Technique: Practical Considerations

Ever‐increasing precision in isotope ratio measurements requires a concomitant small bias within and between laboratories. The double spike technique is the most suitable method to obtain reliable isotope composition data that are accurately corrected for instrumental mass fractionation. Compared with other methods, such as sample‐calibrator bracketing (SCB), only the double spike technique can correct for all sources of fractionation after equilibration of the sample with the double spike, such as that incurred during chemical separation and measurement. In addition, it is not dependent on a priori assumptions of perfect matrix matching of samples to reference materials or quantitative recovery of the sample through the chemical separation procedure to yield accurate results. In this review article, we present a detailed discussion of the merits of the double spike technique, how to design and calibrate a suitable double spike and analytical strategies. Our objective is to offer a step‐by‐step introduction to the use of the double spike technique in order to lower potential barriers that researchers new to the subject might face, such that double spiking will replace SCB as the measurement method of choice.