基于次溴酸钠氧化−氨基磺酸还原测定沉积物<sup>15</sup>N加富培养样品中的<sup>15</sup><inline-formula><tex-math id="Z-20211117095056">\begin{document}${{\bf{NH}}}^{{\bf{+}}}_{{\bf 4}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-14xuhaoming_Z-20211117095056.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-14xuhaoming_Z-20211117095056.png"/></alternatives></inline-formula>的方法探索

徐颢铭; 宋国栋; 刘素美; 梁生康; 张桂玲

doi:10.12284/hyxb2022024

基于次溴酸钠氧化−氨基磺酸还原测定沉积物¹⁵N加富培养样品中的¹⁵${{\bf{NH}}}^{{\bf{+}}}_{{\bf 4}}$的方法探索

doi: 10.12284/hyxb2022024

徐颢铭^{1, 2, 3,},
宋国栋^{1, 2, ,},
刘素美^{1, 2},
梁生康^{1, 2},
张桂玲^{1, 2}

1.
中国海洋大学深海圈层与地球系统前沿科学中心/海洋化学理论与工程技术教育部重点实验室, 山东青岛 266100
2.
青岛海洋科学与技术试点国家实验室海洋生态与环境科学功能实验室, 山东青岛 266237
3.
中国海洋大学化学化工学院, 山东青岛 266100

基金项目: 国家自然科学基金（42076035，U1806211，41606093）；国家重点研发计划（2016YFA0601302）；中国海洋大学中央高校基本科研业务（202072002）。

详细信息

作者简介:
徐颢铭(1998—)，男，辽宁省沈阳市人，主要从事海洋生物地球化学研究。E-mail: richard980126@163.com

通讯作者:
宋国栋，男，副教授，主要从事海洋生物地球化学研究。E-mail: gsong@ouc.edu.cn

中图分类号: P734.2⁺4
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出版历程
- 收稿日期: 2021-07-20
- 修回日期: 2021-09-26
- 网络出版日期: 2021-10-20
- 刊出日期: 2022-01-14

A sodium hypobromite oxidation-sulfamic acid reduction method for determination of ¹⁵$ {\bf{NH_4^+}}$ in ¹⁵N enrichment sediment slurry incubation samples

Xu Haoming^{1, 2, 3
,},
Song Guodong^{1, 2
, ,},
Liu Sumei^{1, 2},
Liang Shengkang^{1, 2},
Zhang Guiling^{1, 2}

1.
Frontiers Science Center for Deep Ocean Multispheres and Earth System/Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
2.
Laboratory for Marine Ecology and Environmental Science, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
3.
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China

摘要

摘要: 沉积物中的异化硝酸盐还原过程是海洋中活性氮转化的关键过程之一。不同于反硝化和厌氧铵氧化，异化硝酸盐还原为铵(DNRA)是将硝酸盐直接还原为铵，而不是以氮气的形态移除，这有可能会加重水体富营养化和缺氧。目前测定沉积物中异化硝酸盐还原过程的主要手段是¹⁵N标记培养技术。为了准确评估DNRA的潜在速率，首先要准确测定加富样品中的¹⁵${\rm {NH}}_4^+ $浓度。常用测定¹⁵${\rm {NH}}_4^+ $的方法为基于次溴酸钠−碘氧化膜进样的四极杆质谱法。然而此方法的分析物之一³⁰N₂在分析时容易存在两个问题而导致结果失真：一是易受样品中O₂干扰而导致³⁰N₂含量被显著高估；二是³⁰N₂在检测器中平衡较慢从而导致测试时间较长且精密度较差。为解决上述问题，本研究采用次溴酸钠氧化−氨基磺酸还原的方法将¹⁵${\rm {NH}}_4^+ $转化为²⁹N₂后通过膜进样的四极杆质谱仪进行测定(简称Redox-MIMS法)。结果表明，Redox-MIMS法在氨基磺酸还原剂浓度为80～100 mmol/L时还原效率最好；方法的检测限约为0.5 μmol/L，精密度为0.8%，工作曲线的线性范围可以达到0～150 μmol/L。相对于次溴酸钠−碘氧化法，Redox-MIMS法反应条件温和，反应试剂相对易得，产物为²⁹N₂，有效解决了³⁰N₂分析的一系列问题，并显著提高了测定效率(2 min/样品)。分别采用Redox-MIMS法和次溴酸钠−碘氧化法测定莱州湾沉积物实际样品，两种方法所测得的DNRA速率以及DNRA占异化硝酸盐还原的比例均无显著性差异，证明Redox-MIMS法是一种准确、高效地测定¹⁵N加富培养样品中¹⁵${\rm {NH}}_4^+ $的方法。
- 沉积物 /
- 氮循环 /
- 异化硝酸盐还原为铵 /
- 膜进样质谱 /
- 次溴酸钠氧化−氨基磺酸还原
Abstract: Dissimilatory nitrate reduction in marine sediment is one of the key nitrogen loss processes in the ocean. Dissimilatory nitrate reduction to ammonium (DNRA), unlike denitrification and anammox by which nitrate is reduced to N₂ and removed from the environment eventually, directly reduce nitrate to ammonium, could lead to eutrophication and water hypoxia afterwards. ¹⁵N labeled technique is the main method to investigate dissimilatory nitrate reduction processes in sediments. Accurate determination of ¹⁵${\rm {NH}}_4^+ $ in isotope enrichment samples is primarily required to evaluate the potential rate of DNRA. The commonly used method for the determination of ¹⁵${\rm {NH}}_4^+ $ at present is the hypobromite iodine oxidation-membrane inlet quadrupole mass spectrometer determination method. However, ³⁰N₂ as the final analyte of the method has two problems which lead to an analysis error: firstly, ³⁰N₂ determined can be significantly overestimated due to the O₂ interference; secondly, the low equilibrium rate of ³⁰N₂ in the detector could influence the precision of the method and low down the analysis speed. To solve the problems mentioned, a sodium hypobromite oxidation-sulfamic acid reduction method by which ¹⁵${\rm {NH}}_4^+ $ is transformed to ²⁹N₂ only and detected using membrane inlet quadrupole mass spectrometer afterwards (Redox-MIMS method) is reported in this article. The results indicate that the optical concentration of sulfamic acid is 80−100 mmol/L; the detection limit is 0.5 μmol/L and the precision (RSD) is 0.8%; the dynamic range of standard curve is 0−150 μmol/L. Comparing with the hypobromite iodine oxidation method, the Redox-MIMS method not only has the advantages of mild reaction conditions and easily obtained reagents, the memory effect of ³⁰N₂ in the detector can also be solved effectively for most of the produced ¹⁵N₂ is ²⁹N₂ which improves detection efficiency (2 min per sample) meanwhile. Determination results of rates of DNRA and the contribution of DNRA to all dissimilatory nitrate reduction processes in the Laizhou Bay sediments using both hypobromite iodine oxidation and Redox-MIMS methods shows no significant difference. These make the Redox-MIMS method an accurate and high-efficient method for determination of ¹⁵${\rm {NH}}_4^+ $ in isotope enrichment samples.
- sediment /
- nitrogen cycling /
- dissimilatory nitrate reduction to ammonium /
- membrane inlet mass spectrometer /
- sodium hypobromite oxidation-sulfamic acid reduction

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图 1 OX-MIMS法(a)和Redox-MIMS法(b)的操作流程

Fig. 1 Procedures of OX-MIMS method (a) and Redox-MIMS method (b)

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图 2 沉积物采样站位

Fig. 2 Sediment sampling stations

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图 3 氨基磺酸最佳浓度测试

Fig. 3 Test for the optical concentration of sulfamic acid

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图 4 Redox-MIMS法标准曲线的线性范围

Fig. 4 Linear range of standard curve using Redox-MIMS method

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图 5 OX-MIMS法（a）和Redox-MIMS法（b）测定产生²⁹N₂和³⁰N₂的比例

Fig. 5 Ratios of ²⁹N₂ and ³⁰N₂ produced using OX-MIMS method (a) and Redox-MIMS method (b)

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图 6 OX-MIMS法（a）和Redox-MIMS法（b）测定的曲线

Fig. 6 Detection curve using OX-MIMS method (a) and Redox-MIMS method (b)

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图 7 莱州湾H1-7、S5、H2-7站位沉积物不同¹⁵N加富培养体系中¹⁵N₂和¹⁵$ {\rm{NH}}_4^+$浓度随时间变化

a1−a3. 加富¹⁵$ {\rm{NO}}_3^-$，产生¹⁵N₂; b1−b3. 加富¹⁵$ {\rm{NH}}_4^+$，产生¹⁵N₂; c1−c3. 加富¹⁵$ {\rm{NH}}_4^+$+¹⁴$ {\rm{NO}}_3^-$，产生¹⁵N₂; d1−d3. 加富¹⁵$ {\rm{NO}}_3^-$，产生¹⁵$ {\rm{NH}}_4^+$

Fig. 7 ¹⁵N₂ and¹⁵$ {\rm{NH}}_4^+$ concentration production with time changes in different ¹⁵N tracer enrichment incubation systems of sediments in stations H1-7, S5, H2-7 in the Laizhou Bay

a1−a3.¹⁵$ {\rm{NO}}_3^{-}$ enrichment with ¹⁵N₂ produced; b1−b3. ¹⁵$ {\rm{NH}}_4^{+}$ enrichment with ¹⁵N₂ produced; c1−c3. ¹⁵$ {\rm{NH}}_4^+$+¹⁴$ {\rm{NO}}_3^{-}$ enrichment with ¹⁵N₂ produced; d1−d3. ¹⁵$ {\rm{NO}}_3^{-}$ enrichment with ¹⁵$ {\rm{NH}}_4^+$ produced

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图 8 各站位异化硝酸盐还原速率占比情况

Fig. 8 Proportion of each dissimilatory nitrate reduction process in different stations

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图 9 采用两种方法测定的DNRA潜在速率以及x_DNRA值

Fig. 9 Determination results of DNRA potential rates and x_DNRA using two different methods

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