We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
The influence of sample matrix on the accuracy of nitrite N and O isotope ratio analyses with the azide method.
- Authors
Granger, Julie; Boshers, Danielle S.; Böhlke, John K.; Yu, Dan; Chen, Nengwang; Tobias, Craig R.
- Abstract
Rationale: The isotope ratios of nitrogen (15N/14N) and oxygen (18O/16O) in nitrite (NO2−) can be measured by conversion of the nitrite into nitrous oxide (N2O) with azide, followed by mass spectrometric analysis of N2O by gas chromatography isotope ratio mass spectrometry (GC/IRMS). While applying this method to brackish samples, we noticed that the N and O isotope ratio measurements of NO2− are highly sensitive to sample salinity and to the pH at which samples are preserved. Methods: We investigated the influence of sample salinity and sample preservation pH on the N and O isotope ratios of the N2O produced from the reaction of NO2− with azide. The N2O isotope ratios were measured by GC/IRMS. Results: Under the experimental reaction conditions, the conversion of NO2− into N2O was less complete in lower salinity solutions, resulting in respective N and O isotopic offsets of +2.5‰ and −14.0‰ compared with seawater solutions. Differences in salinity were also associated with differences in the fraction of O atoms exchanged between NO2− and water during the reaction. Similarly, aqueous NO2− samples preserved at elevated pH values resulted in the incomplete conversion of NO2− into N2O by azide, and consequent pH‐dependent isotopic offsets, as well as differences in the fraction of O atoms exchanged with water. The addition of sodium chloride to the reaction matrix of samples and standards largely mitigated salinity‐dependent isotopic offsets in the N2O product, and nearly homogenized the fraction of O atom exchange among samples of different salinity. A test of the hypobromite–azide method to measure N isotope ratios of ammonium by conversion into NO2− then N2O revealed no influence of sample salinity on the N isotope ratios of the N2O product. Conclusions: We outline recommendations to mitigate potential matrix effects among samples and standards, to improve the accuracy of N and O isotope ratios in NO2− measured with the azide method.
- Subjects
ISOTOPIC analysis; OXYGEN isotopes; RATIO analysis; MATRIX effect; NITROGEN isotopes; GAS analysis; NITRITES
- Publication
Rapid Communications in Mass Spectrometry: RCM, 2020, Vol 34, Issue 1, pN.PAG
- ISSN
0951-4198
- Publication type
Article
- DOI
10.1002/rcm.8569