Essentials of iron, chromium, and calcium isotope analysis of natural materials by thermal ionization mass spectrometry
Essentials of iron, chromium, and calcium isotope analysis of natural materials by thermal ionization mass spectrometry
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DOI：
10.1016/j.chemgeo.2008.06.018
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发表时间：
2009-01
期刊：
影响因子：
3.9
通讯作者：
M. Fantle;T. Bullen
中科院分区：
文献类型：
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作者：
M. Fantle;T. Bullen
近年来，利用同位素来了解金属在地质、水文和生物系统中的行为迅速扩大。用于分析金属同位素的质谱技术之一是热电离质谱，或TIMS。虽然TIMS几十年来一直是测量同位素组成的有用分析技术，并且TIMS仪器分布广泛，但使用TIMS分析较轻碱土元素和过渡金属的同位素存在显著困难。克服这些困难，从微克大小的样品产生相对长寿命和稳定的离子束是一个不平凡的任务。我们在这里集中在三个地质和环境重要元素（铁，铬和钙）的TIMS分析，并提出了深入研究几个关键方面，我们认为有最大的潜力麻烦新用户。我们的讨论包括不同的分析方法和问题，包括灯丝加载程序，收集杯配置，峰形和干扰，以及使用同位素双尖峰和相关的误差估计访问的描述。在以前工作的基础上，我们提出了定量模拟，特别是在这项研究中应用到铁和钙，探讨（1）时变蒸发的同位素均匀的斑点从灯丝和（2）来自双尖峰减法例程的同位素比的干扰的影响。我们讨论了尖峰质量以及其他测量质量的干扰如何以及在多大程度上影响感兴趣的双尖峰扣除同位素比（在所介绍的情况下为44 Ca/40 Ca，尽管类似的分析可用于评估56 Fe/54 Fe和53 Cr/52 Cr）。这些模拟的结论既不直观也不明显，这使得这项研究对那些正在开发新方法的人很有用。虽然所有模拟都是在特定同位素系统的背景下进行的，但应注意，相同的方法可用于评估任何感兴趣的同位素系统。
The use of isotopes to understand the behavior of metals in geological, hydrological, and biological systems has rapidly expanded in recent years. One of the mass spectrometric techniques used to analyze metal isotopes is thermal ionization mass spectrometry, or TIMS. While TIMS has been a useful analytical technique for the measurement of isotopic composition for decades and TIMS instruments are widely distributed, there are significant difficulties associated with using TIMS to analyze isotopes of the lighter alkaline earth elements and transition metals. Overcoming these difficulties to produce relatively long-lived and stable ion beams from microgram-sized samples is a non-trivial task. We focus here on TIMS analysis of three geologically and environmentally important elements (Fe, Cr, and Ca) and present an in-depth look at several key aspects that we feel have the greatest potential to trouble new users. Our discussion includes accessible descriptions of different analytical approaches and issues, including filament loading procedures, collector cup configurations, peak shapes and interferences, and the use of isotopic double spikes and related error estimation. Building on previous work, we present quantitative simulations, applied specifically in this study to Fe and Ca, that explore the effects of (1) time-variable evaporation of isotopically homogeneous spots from a filament and (2) interferences on the isotope ratios derived from a double spike subtraction routine. We discuss how and to what extent interferences at spike masses, as well as at other measured masses, affect the double spike-subtracted isotope ratio of interest (44Ca/40Ca in the case presented, though a similar analysis can be used to evaluate56Fe/54Fe and53Cr/52Cr). The conclusions of these simulations are neither intuitive nor immediately obvious, making this examination useful for those who are developing new methodologies. While all simulations are carried out in the context of a specific isotope system, it should be noted that the same methods can be used to evaluate any isotope system of interest.