Advances in multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) have led to the widespread use of iron (Fe) isotopes to elucidate the (bio)geochemical history of a range of environments. To generate Fe isotope ratio measurements, standard-sample bracketing (SSB) is commonly used to correct for instrumental mass bias inherent to MC-ICP-MS. However, SSB is only accurate when sample and isotope standard Fe concentrations match, in addition to the bulk solution matrix. When the Fe concentrations differ, Fe isotope ratio measurement results may be inaccurate, a phenomenon known as the "self-induced matrix effect." This study systematically characterised the self-induced matrix effect for dry plasma Fe isotope ratio measurements on three MC-ICP-MS instruments and three introduction systems. Our extensive dataset indicates that: (1) the degree of mass bias is consistent regardless of MC-ICP-MS front-end design, (2) the degree of mass bias becomes less reproducible as the concentration difference between the sample and bracketing standard increases, and (3) this applies to both pure Fe solutions and solutions from geological materials. This study reinforces the requirement to match bracketing standard and sample concentrations within 10% and provides a correction method for that fall beyond the recommended concentration range to subsequently allow for proper concentration matching during SSB.

中文翻译：

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MC-ICP-MS 铁同位素测量过程中标准样品浓度不匹配影响的系统研究

多接收器电感耦合等离子体质谱 (MC-ICP-MS) 的进步导致铁 (Fe) 同位素的广泛使用来阐明一系列环境的（生物）地球化学历史。为了生成 Fe 同位素比测量值，通常使用标准样品包围 (SSB) 来校正 MC-ICP-MS 固有的仪器质量偏差。然而，除了本体溶液基质之外，只有当样品和同位素标准 Fe 浓度匹配时，SSB 才是准确的。当Fe浓度不同时，Fe同位素比测量结果可能不准确，这种现象称为“自致基质效应”。本研究系统地表征了在三台 MC-ICP-MS 仪器和三个引入系统上进行干等离子体铁同位素比测量时的自感基质效应。我们广泛的数据集表明：(1) 无论 MC-ICP-MS 前端设计如何，质量偏差程度都是一致的，(2) 随着样品和包围标准之间的浓度差异增加，质量偏差程度的重现性降低，(3) 这适用于纯铁溶液和地质材料溶液。这项研究强调了将括号标准品和样品浓度匹配在 10% 以内的要求，并提供了超出推荐浓度范围的校正方法，以便随后在 SSB 期间进行适当的浓度匹配。