A protocol for nitrogen isotopic measurement of dissolved organic nitrogen with a combination of oxidation-denitrification and gas phase diffusion methods
A protocol for nitrogen isotopic measurement of dissolved organic nitrogen with a combination of oxidation-denitrification and gas phase diffusion methods
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DOI：
10.1080/10256016.2021.1948411
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发表时间：
2021-07-08
影响因子：
1.3
通讯作者：
Nishida, Kei
中科院分区：
文献类型：
--
作者：
Cao, Hai Thi Thuy;Nakamura, Takashi;Nishida, Kei
同位素示踪技术是研究水环境中氮素来源和去向的最有效方法之一。溶解有机氮（DON）是氮循环的重要组成部分，但由于直接测定的回收率较低，DON中氮稳定同位素比值（δ N-15-DON）的信息有限。间接测量基于质量平衡计算，易于使用，DON回收率高。然而，理论上，质量平衡计算结果对DON含量的高低较为敏感，其适用性还有待于对总溶解氮（TDN）中DON含量不同的沃茨进行检验。在这项研究中，我们建立了一个协议的基础上，多种分析方法的组合间接测量Δ N-15-DON值。通过改变DON和溶解无机氮的组成来评估测量的精密度和准确度，并在不同的可接受水平下呈现定量阈值。结果表明，所开发的协议可能适用于水样，特别是低DON含量，通常在淡水中检测到的优势。这种方法有望扩大同位素示踪技术的使用，以了解水环境中的氮循环。
Isotopic tracing technique is one of the most effective methods to identify nitrogen source and fate in aquatic environments. Although dissolved organic nitrogen (DON) is a key component in nitrogen cycles, information on nitrogen stable isotope ratios in DON (delta N-15-DON) is limitedly available for its low recovery through a direct measurement. Indirect measurement is based on mass balance calculations and easy to use with high recovery of DON. However, in theory, the result from mass balance calculation is sensitive to the level of DON content, and its applicability remains to be examined for waters containing a variety of DON content in total dissolved nitrogen (TDN). In this study, we established a protocol for indirect measurement of delta N-15-DON values based on the combination of multiple analytical methods. Precision and accuracy in the measurement were assessed by varying the composition of DON and dissolved inorganic nitrogen, and quantitation thresholds were presented at different acceptable levels. The results illustrated an advantage of the developed protocol possibly applicable to water samples particularly with low DON content that is commonly detected in freshwater. This method is expected to expand the use of isotope tracing techniques for understanding the nitrogen cycle in water environments.