Magyar, Paul M. and Orphan, Victoria J. and Eiler, John M. (2016) Measurement of rare isotopologues of nitrous oxide by high-resolution multi-collector mass spectrometry. Rapid Communications in Mass Spectrometry, 30 (17). pp. 1923-1940. ISSN 0951-4198. http://resolver.caltech.edu/CaltechAUTHORS:20160808-234129625
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Rationale: 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 N_2O sources. Methods: We describe a technique to measure six singly and doubly substituted isotopic variants of N2O, 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 N_2O. Results: We demonstrate the precision and accuracy of these measurements by analyzing N_2O 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 N_2O from a denitrifying bacterium suggests that its clumped isotopic composition is controlled by kinetic isotope effects in N_2O production. Conclusions: We developed a method for measuring six isotopic variants of N_2O and tested it with analyses of biogenic N_2O. The added isotopic constraints provided by these measurements will enhance our ability to apportion N_2O sources.
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|Additional Information:||© 2016 John Wiley & Sons, Ltd. Version of record online: 5 August 2016; Manuscript Accepted: 18 June 2016; Manuscript Revised: 16 June 2016; Manuscript Received: 16 March 2016. This work was supported by a grant from the Gordon and Betty Moore Foundation Marine Microbiology Initiative (Grant #3306) and by NSF-EAR. We thank Dianne Newman for providing the P. aeruginosa ∆nosZ mutant and for the use of her laboratory; Sebastian Kopf for aid in microbial culturing; Nami Kitchen for assistance in the laboratory; and Daniel Stolper, Alison Piasecki, and Matthieu Clog for helpful discussions. We thank Karen Casciotti, Shuhei Ono, and Nathaniel Ostrom for providing calibrated reference samples and Sakae Toyoda and Naohiro Yoshida for measuring the isotopic composition of our reference gas. Finally, we thank Nathaniel Ostrom for helpful comments on an an earlier draft of this manuscript, as well as two anonymous reviewers for their comments.|
|Official Citation:||Magyar, P. M., Orphan, V. J., and Eiler, J. M. (2016) Measurement of rare isotopologues of nitrous oxide by high-resolution multi-collector mass spectrometry. Rapid Commun. Mass Spectrom., 30: 1923–1940. doi: 10.1002/rcm.7671|
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|Deposited On:||09 Aug 2016 17:38|
|Last Modified:||09 Aug 2016 17:38|
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