Magyar Paul M, Orphan Victoria J, Eiler John M
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA.
Rapid Commun Mass Spectrom. 2016 Sep 15;30(17):1923-40. doi: 10.1002/rcm.7671.
Bulk and position-specific stable isotope characterization of nitrous oxide represents one of the most powerful tools for identifying its environmental sources and sinks. Constraining (14) N(15) N(18) O and (15) N(14) N(18) O will add two new dimensions to our ability to uniquely fingerprint N2 O sources.
We describe a technique to measure six singly and doubly substituted isotopic variants of N2 O, constraining the values of δ(15) N, δ(18) O, ∆(17) O, (15) N site preference, and the clumped isotopomers (14) N(15) N(18) O and (15) N(14) N(18) O. The technique uses a Thermo MAT 253 Ultra, a high-resolution multi-collector gas source isotope ratio mass spectrometer. It requires 8-10 hours per sample and ~10 micromoles or more of pure N2 O.
We demonstrate the precision and accuracy of these measurements by analyzing N2 O brought to equilibrium in its position-specific and clumped isotopic composition by heating in the presence of a catalyst. Finally, an illustrative analysis of biogenic N2 O from a denitrifying bacterium suggests that its clumped isotopic composition is controlled by kinetic isotope effects in N2 O production.
We developed a method for measuring six isotopic variants of N2 O and tested it with analyses of biogenic N2 O. The added isotopic constraints provided by these measurements will enhance our ability to apportion N2 O sources.
一氧化二氮的体积和位置特异性稳定同位素表征是识别其环境源和汇的最有力工具之一。限制（14）N（15）N（18）O和（15）N（14）N（18）O将为我们独特地识别N2O源的能力增加两个新维度。
我们描述了一种测量N2O的六种单取代和双取代同位素变体的技术，该技术可限制δ（15）N、δ（18）O、∆（17）O、（15）N位置偏好以及聚集同位素异构体（14）N（15）N（18）O和（15）N（14）N（18）O的值。该技术使用Thermo MAT 253 Ultra，一种高分辨率多收集器气体源同位素比率质谱仪。每个样品需要8 - 10小时，且需要约10微摩尔或更多的纯N2O。
我们通过分析在催化剂存在下加热使其位置特异性和聚集同位素组成达到平衡的N2O，证明了这些测量的精度和准确性。最后，对来自反硝化细菌的生物源N2O的示例分析表明，其聚集同位素组成受N2O产生过程中的动力学同位素效应控制。
我们开发了一种测量N2O六种同位素变体的方法，并通过对生物源N2O的分析对其进行了测试。这些测量提供的额外同位素限制将增强我们分配N2O源的能力。
