Wassenaar L I, Terzer-Wassmuth S, Douence C, Araguas-Araguas L, Aggarwal P K, Coplen T B
International Atomic Energy Agency, Isotope Hydrology Section, PO Box 100, A-1400, Vienna, Austria.
US Geological Survey, 431 National Center, 12201Sunrise Valley Drive, Reston, VA, 20192, USA.
Rapid Commun Mass Spectrom. 2018 Mar 15;32(5):393-406. doi: 10.1002/rcm.8052.
Water stable isotope ratios (δ H and δ O values) are widely used tracers in environmental studies; hence, accurate and precise assays are required for providing sound scientific information. We tested the analytical performance of 235 international laboratories conducting water isotope analyses using dual-inlet and continuous-flow isotope ratio mass spectrometers and laser spectrometers through a water isotope inter-comparison test.
Eight test water samples were distributed by the IAEA to international stable isotope laboratories. These consisted of a core set of five samples spanning the common δ-range of natural waters, and three optional samples (highly depleted, enriched, and saline). The fifth core sample contained unrevealed trace methanol to assess analyst vigilance to the impact of organic contamination on water isotopic measurements made by all instrument technologies.
For the core and optional samples ~73 % of laboratories gave acceptable results within 0.2 ‰ and 1.5 ‰ of the reference values for δ O and δ H, respectively; ~27 % produced unacceptable results. Top performance for δ O values was dominated by dual-inlet IRMS laboratories; top performance for δ H values was led by laser spectrometer laboratories. Continuous-flow instruments yielded comparatively intermediate results. Trace methanol contamination of water resulted in extreme outlier δ-values for laser instruments, but also affected reactor-based continuous-flow IRMS systems; however, dual-inlet IRMS δ-values were unaffected.
Analysis of the laboratory results and their metadata suggested inaccurate or imprecise performance stemmed mainly from skill- and knowledge-based errors including: calculation mistakes, inappropriate or compromised laboratory calibration standards, poorly performing instrumentation, lack of vigilance to contamination, or inattention to unreasonable isotopic outcomes. To counteract common errors, we recommend that laboratories include 1-2 'known' control standards in all autoruns; laser laboratories should screen each autorun for spectral contamination; and all laboratories should evaluate whether derived d-excess values are realistic when both isotope ratios are measured. Combined, these data evaluation strategies should immediately inform the laboratory about fundamental mistakes or compromised samples.
水稳定同位素比率（δH和δO值）是环境研究中广泛使用的示踪剂；因此，需要准确精确的分析来提供可靠的科学信息。我们通过一项水同位素比对测试，检验了235个使用双进样和连续流同位素比率质谱仪以及激光光谱仪进行水同位素分析的国际实验室的分析性能。
国际原子能机构向国际稳定同位素实验室分发了8个测试水样。这些水样包括一组由5个样品组成的核心样品，涵盖天然水常见的δ范围，以及3个可选样品（高度贫化、富集和含盐）。第五个核心样品含有未公开的痕量甲醇，以评估分析人员对有机污染对所有仪器技术进行水同位素测量影响的警觉性。
对于核心样品和可选样品，分别有73%的实验室给出的δO和δH结果在参考值的0.2‰和1.5‰范围内，可接受；27%的实验室给出的结果不可接受。双进样同位素比率质谱仪实验室在δO值的分析中表现最佳；激光光谱仪实验室在δH值的分析中表现最佳。连续流仪器得出的结果相对居中。水中痕量甲醇污染导致激光仪器的δ值出现极端异常值，但也影响了基于反应器的连续流同位素比率质谱仪系统；然而，双进样同位素比率质谱仪的δ值不受影响。
对实验室结果及其元数据的分析表明，不准确或不精确的性能主要源于基于技能和知识的错误，包括：计算错误、实验室校准标准不当或受损、仪器性能不佳、对污染缺乏警觉或对不合理的同位素结果不关注。为了应对常见错误，我们建议实验室在所有自动运行中纳入1 - 2个“已知”对照标准；激光实验室应在每次自动运行中筛查光谱污染；所有实验室在测量两种同位素比率时都应评估导出的d值是否合理。综合起来，这些数据评估策略应能立即告知实验室基本错误或有问题的样品情况。
