In:
Frontiers in Environmental Science, Frontiers Media SA, Vol. 10 ( 2022-5-17)
Kurzfassung:
Nitrogen (N) isotope ratios (δ 15 N) of multiple N species including ammonium (NH 4 + ), nitrate (NO 3 − ), dissolved organic N (DON), and total dissolved N (TDN) can serve as indicators of the sources of wet N deposition. However, methods for sequential analysis of these multiple N species are not well developed. In this study, methods for the determination of δ 15 N of these multiple N species were proposed through a traditional distillation method for NH 4 + and NO 3 − , direct evaporation for TDN, and an isotope mass balance equation for δ 15 N-DON. A series of experiments were conducted 1) to find evaporation conditions including pH ( & lt;3.5 vs. 5.4) and evaporation methods (oven drying at 60 and 100°C, infra-red chamber, and freeze-drying), 2) to investigate precision and accuracy of distillation for δ 15 N of NH 4 + and NO 3 − , and 3) to determine δ 15 N-TDN by direct evaporation and δ 15 N-DON with mass balance equation. (NH 4 ) 2 SO 4 (‒4.0 ± 0.03‰), KNO 3 (‒4.2 ± 0.03‰), and CO(NH 2 ) 2 (‒5.4 ± 0.04‰) were used as reference materials for NH 4 + , NO 3 − , and DON, respectively. In this study, for the analysis of δ 15 N of NH 4 + and NO 3 − , the conventional distillation method was tested in an effort to save cost for laboratories equipped with the distillation system. Evaporation using oven at 60°C (but not 100°C), infra-red chamber, or freeze-drier after acidification to & lt; pH 3.5 prevented 14 NH 3 loss. Analysis of the δ 15 N-NO 3 − (‒4.4 ± 0.1‰ to ‒3.9 ± 0.5‰) was reliable for a wide range of N content (0.1–0.5 mg), but analytical errors for δ 15 N-NH 4 + were as high as 2.1‰ when N content was small (e.g., 0.1–0.3 mg N) due to background contamination and potential interference by co-existing DON. Direct evaporation of solution containing NH 4 + , NO 3 − , and DON to dryness produced reliable δ 15 N-TDN with accuracy & lt;0.15‰ and precision & lt;0.21‰. However, the analytical errors of δ 15 N-DON were highly dependent on the content of co-existing NH 4 + as well as DON content. Therefore, the proposed protocol can be applied for rainwater containing a high NH 4 + concentration ( & gt;2.0 mg N L −1 assuming that 200 ml of sample is used for distillation).
Materialart:
Online-Ressource
ISSN:
2296-665X
DOI:
10.3389/fenvs.2022.877055
Sprache:
Unbekannt
Verlag:
Frontiers Media SA
Publikationsdatum:
2022
ZDB Id:
2741535-1
Permalink