Abstract Stable barium isotope measurements with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) remain an analytical challenge and can be considerably affected by the presence of matrix elements, even when applying double spiking. Therefore significant efforts were invested in previous studies to develop efficient barium purification methods. However, due to the high variability in matrix/barium ratios for diverse sample matrices, potential matrix effects can still not be excluded. While a lot of effort has been invested into improving the chemical separation protocols, the impact of plasma conditions on the accuracy and precision of stable isotope measurements has rarely been considered. Here we present a systematic investigation of the relationship between plasma conditions, instrumental mass fractionation (IMF) and impurity (i.e. matrix) concentrations. The Normalised Ar Index (NAI) and Matrix-Ar Index (MA) are used to quantify MC-ICP-MS plasma conditions and plasma mass loading, respectively. Our results show that the effect of matrix elements on IMF is largely linked to plasma conditions (i.e. NAI) and behaves as a linear function of mass loading (i.e. MA). Accordingly, the matrix effects can be significantly attenuated by increasing the NAI thereby minimising the risk of plasma “over-loading”. The improved understanding of the behaviour of the matrix-induced IMF allows us to define a matrix tolerance plasma state for barium isotope analysis. The accuracy of this recommended method is further assessed by analyses of two well-studied reference materials, the GEOTRACES seawater reference sample SAFe D2 and the carbonate reference material JCp-1. We expect that the analytical protocol described in this study is applicable not only to barium isotope analysis, but also to a wide range of other stable isotope measurements with MC-ICP-MS.

中文翻译：

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MC-ICP-MS 等离子体条件对钡同位素稳定同位素测量准确度和精密度的影响

摘要 使用多接收器电感耦合等离子体质谱 (MC-ICP-MS) 进行稳定的钡同位素测量仍然是一项分析挑战，并且会受到基质元素存在的显着影响，即使在应用双加标时也是如此。因此，以前的研究投入了大量精力来开发有效的钡纯化方法。然而，由于不同样品基质的基质/钡比率的高度可变性，仍然不能排除潜在的基质效应。尽管已投入大量精力改进化学分离方案，但很少考虑等离子体条件对稳定同位素测量的准确性和精确度的影响。在这里，我们对等离子体条件之间的关系进行了系统的研究，仪器质量分馏 (IMF) 和杂质（即基质）浓度。归一化 Ar 指数 (NAI) 和基质-Ar 指数 (MA) 分别用于量化 MC-ICP-MS 等离子体条件和等离子体质量负载。我们的结果表明，基质元素对 IMF 的影响在很大程度上与等离子体条件（即 NAI）相关，并且表现为质量负载（即 MA）的线性函数。因此，可以通过增加 NAI 来显着减弱基质效应，从而最大限度地降低血浆“过载”的风险。对基质诱导 IMF 行为的更好理解使我们能够为钡同位素分析定义基质耐受等离子体状态。通过对两种经过充分研究的参考材料的分析，进一步评估了该推荐方法的准确性，GEOTRACES 海水参考样品 SAFe D2 和碳酸盐参考材料 JCp-1。我们预计本研究中描述的分析方案不仅适用于钡同位素分析，而且适用于使用 MC-ICP-MS 进行的各种其他稳定同位素测量。