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首页> 外文期刊>Journal of mass spectrometry: JMS >Methods and limitations of 'clumped' CO2 isotope (Delta(47)) analysis by gas-source isotope ratio mass spectrometry
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Methods and limitations of 'clumped' CO2 isotope (Delta(47)) analysis by gas-source isotope ratio mass spectrometry

机译：气源同位素比率质谱法分析“结块” CO2同位素（Delta（47））的方法和局限性

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The geochemistry of multiply substituted isotopologues ('clumped-isotope' geochemistry) examines the abundances in natural materials of molecules, formula units or moieties that contain more than one rare isotope (e.g. (COO)-C-13-O-18-O-16, (OO)-O-18-O-18, N-15(2), (COO22-)-C-13-O-18-O-16). Such species form the basis of carbonate clumped-isotope thermometry and undergo distinctive fractionations during a variety of natural processes, but initial reports have provided few details of their analysis. In this study, we present detailed data and arguments regarding the theoretical and practical limits of precision, methods of standardization, instrument linearity and related issues for clumped-isotope analysis by dual-inlet gas-source isotope ratio mass spectrometry (IRMS). We demonstrate long-term stability and subtenth per mil precision in 47/44 ratios for counting systems consisting of a Faraday cup registered through a 10(12) Omega resistor on three Thermo-Finnigan 253 IRMS systems. Based on the analyses of heated CO2 gases, which have a stochastic distribution of isotopes among possible isotopologues, we document and correct for (1) isotopic exchange among analyte CO2 molecules and (2) subtle nonlinearity in the relationship between actual and measured 47/44 ratios. External precisions of similar to 0.01 parts per thousand are routinely achieved for measurements of the mass-47 anomaly (a measure mostly of the abundance anomaly of C-13-O-18 bonds) and follow counting statistics. The present technical limit to precision intrinsic to our methods and instrumentation is similar to 5 parts per million (ppm), whereas precisions of measurements of heterogeneous natural materials are more typically similar to 10 ppm (both 1 s.e.). These correspond to errors in carbonate clumped-isotope thermometry of +/- 1.2 degrees C and +/- 2.4 degrees C, respectively.
机译：多重取代的同位素同位素的地球化学（“聚集同位素”地球化学）研究了天然材料中包含一种以上稀有同位素（例如（COO）-C-13-O-18-O- 16，（OO）-O-18-O-18，N-15（2），（COO22-）-C-13-O-18-O-16）。这些物种构成了碳酸盐成簇同位素测温的基础，并在各种自然过程中经历了独特的分馏过程，但初步报告很少提供其分析的详细信息。在这项研究中，我们提供了有关双入口气源同位素比质谱法（IRMS）的团簇同位素分析的精密度，标准化方法，仪器线性度和相关问题的理论和实践极限的详细数据和论据。我们演示了计数系统在47/44比率下的长期稳定性和百万分之一精度，该计数系统由在三个Thermo-Finnigan 253 IRMS系统上通过10（12）Omega电阻器记录的法拉第杯组成。基于对加热的CO2气体的分析，这些气体在可能的同位素同位素之间具有同位素的随机分布，我们记录并纠正（1）被分析物CO2分子之间的同位素交换，以及（2）实际与实测值之间的微妙非线性47/44比率。对于质量47异常（通常用于测量C-13-O-18键的丰度异常）的测量，通常可以达到接近千分之千的外部精度，并遵循计数统计。目前，我们的方法和仪器固有的精度技术极限类似于百万分之5（ppm），而异质天然材料的测量精度更典型地类似于10 ppm（均为1 s.e.）。这些分别对应于+/- 1.2摄氏度和+/- 2.4摄氏度的碳酸盐成簇同位素测温法中的误差。

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