Value Assignment and Uncertainty Estimation of Selected Light Stable Isotope Reference Materials: RMs 8543-8545, RMs 8562-8564, and RM 8566 | NIST
Value Assignment and Uncertainty Estimation of Selected Light Stable Isotope Reference Materials: RMs 8543-8545, RMs 8562-8564, and RM 8566 | NIST
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选定的光稳定同位素参考材料的赋值和不确定性估计：RMs 8543-8545、RMs 8562-8564 和 RM 8566 |
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
D. Klinedinst
中科院分区：
文献类型：
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作者：
R. Verkouteren;D. Klinedinst
我们报告了 NIST 和国际原子能机构 (IAEA) 分发的几种碳和氧稳定同位素参考材料的赋值技术基础，并就实验室实践和未来的比对活动提出建议。不确定性的分配和估计基于使用 NIST 的一种方法和外部合作实验室的另一种方法的测量数据。所有方法均基于二氧化碳的同位素比质谱 (IRMS)：外部合作者测量了二氧化碳的三种同量异位形式，而 NIST 测量了四种形式。这项附加功能使 NIST 能够评估测量精度，并设计一种 IRMS 方法，最大限度地减少交叉污染造成的偏差。国际比较活动的设计包括标准化学制剂和同位素测量（按照国际原子能机构标准物质工作组设计的严格要求）对源自碳酸盐、水和纯二氧化碳标准物质的二氧化碳进行测量。我们的目标是确定精确的 δ13C 和 δ18O 值分配，这些值在所有材料中保持一致并校正交叉污染，并将结果的变化与特定的实验室实践联系起来，以指导未来的相互比较。所有参与者的测量数据都汇总在电子表格中，并检查其一致性。通过直接测量这种效应，对满足性能要求的数据进行交叉污染校正，然后使用国际公认的程序进行处理，以确定标准化的 δ13C 和 δ18O 值。对于碳酸盐和 CO2 材料，这种比对的结果提供的值分配稍微偏向更贫化的成分，与之前的分配相比，不确定性提高了多达两倍。对于水材料，结果变化较大，但表明 VSMOW 同位素比标度上 SLAP 的 δ18O 值在 –55.7 ‰ 和 –56.2 ‰ 之间。标准化后，δ18O 值与之前的测定结果一致。使用统计方法来辨别结果和任意因素之间的关系；描述了这些关系。为了研究数据处理中使用的氧同位素组成假设的影响，应用了几组假设。对结果进行比较，并就这些假设的使用以及对数据可比性的影响提出建议。
We report the technical basis for value assignments of several carbon and oxygen stable isotope reference materials distributed by NIST and the International Atomic Energy Agency (IAEA), and make recommendations regarding laboratory practices and future intercomparison exercises. Assignments and estimates of uncertainty are based on measurement data using one method at NIST and another method at outside collaborating laboratories. All methods are based on isotope ratio mass spectrometry (IRMS) of carbon dioxide: outside collaborators measured three isobaric forms of CO2, whereas NIST measured four forms. This additional capability allowed NIST to assess measurement accuracy, and design an IRMS method that minimized bias from cross-contamination. The international comparison exercise was designed, involving standard chemical preparation and isotopic measurement ─ under strict requirements designed by the IAEA-Working Group for Reference Materials ─ of CO2 derived from carbonates, waters, and pure CO2 reference materials. Our goal was to determine precise δC and δO value assignments that were consistent across the materials and corrected for cross-contamination, and to relate variations in results with specific laboratory practices to guide future intercomparisons. Measurement data from all participants were compiled in a spreadsheet and inspected for consistency. Those data meeting the performance requirements were corrected for cross-contamination through direct measurement of this effect, then processed using internationally accepted procedures to determine standardized δC and δO values. For the carbonate and CO2 materials, the results of this intercomparison provide value assignments shifted slighted towards more depleted compositions with uncertainties improved by factors up to two over the previous assignments. For the water materials, results were more variable yet suggested that the δO value of SLAP on the VSMOW isotope ratio scale is between –55.7 ‰ and –56.2 ‰. When normalized, δO values were consistent with prior determinations. Statistical approaches were used to discern relationships between results and discretionary factors; these relationships are described. To investigate the effects of oxygen isotope compositional assumptions used in data processing, several sets of assumptions were applied. Results are compared and recommendations made regarding the use of these assumptions and the effect on intercomparability of data.