| Résumé | High precision determination of isotope ratios has grown exponentially in recent years, as a result of their important and wide range of applications in almost all disciplines including archaeology, provenance studies, medical science, nuclear and forensic sciences, geosciences, and environmental science. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is one of the two most powerful techniques for obtaining accurate and precise isotope amount ratios. Compared to the thermal ionization mass spectrometry (TIMS), MC-ICP-MS exists much larger isotopic fractionation/mass bias. In addition to commonly believed mass-dependent fractionation (MDF) phenomenon, recognition and reporting of mass-independent fractionation (MIF) within MC-ICP-MS itself has proliferated in the last decade. Commonly used traditional isotopic fractionation correction models, such as the widely used Russell law, were designed to account for the MDF only as a function of nuclide mass. Latest findings of MIF within MC-ICP-MS itself have a significant impact on the choice of isotopic fractionation correction models, as the use of mass-dependent models for isotopes which display MIF would result in biased isotope amount ratios. This chapter focuses on the latest developments related to isotopic fractionation and its correction models for obtaining accurate isotope amount ratios by MC-ICP-MS.
多接收器电感耦合等离子体质谱（MC-ICP-MS）是高精度测定同位素比值最常用的两种技术之一，广泛应用于考古学、物源研究、医学、核科学、法医学、地球科学和环境科学等多个学科[1-9]。与传统的热电离质谱（TIMS）相比，MC-ICP-MS的样品引入方式简单，灵敏度高，并具有测量高电离势元素的能力，但它会产生更大的同位素分馏/质量偏倚[1, 7]。用MC-ICP-MS测得锂的同位素比值与真实值之间的偏差高达25%[10] （而TIMS中Li的偏差仅1-2%[11]）。
ICP-MS中出现同位素分馏现象的原因至今还不完全清楚，但很可能是由于离子通过取样锥时的超音速气流膨胀，以及在截取锥区域的空间电荷效应引起的。这两个过程都有利于将较重的同位素传输到质谱仪中，导致整个质量区间产生不均匀的响应（灵敏度）[12-14]。质量偏倚的大小也随操作条件而变化，例如，样品气流速，以及采样锥和等离子体矩管末端之间的距离，即样品深度等[15]。此外，同位素分馏也随时间而漂移，并受到样品基体的影响。因此，合适的质量偏倚校正是MC-ICP-MS获得精准同位素比值的关键 |
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