引用本文:	罗畅,宋国栋,刘素美.基于双还原体系与膜进样质谱快速测定¹⁵N加富水样中¹⁵NO₃^-的方法.海洋与湖沼,2022,53(2):320-329.

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基于双还原体系与膜进样质谱快速测定¹⁵N加富水样中¹⁵NO₃^-的方法
罗畅^1,2,3, 宋国栋^1,2, 刘素美^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

摘要:

海洋中的氮循环是海洋生物地球化学研究的热点领域之一,而硝化过程是氮循环的关键一环,准确获取硝化速率对于丰富海洋氮循环的认识至关重要。¹⁵N标记同位素技术是目前国际上最为广泛使用的硝化速率测定方法,该方法的核心在于准确测定¹⁵N加富样品产生的¹⁵NO^-₂和¹⁵NO₃^-的含量,但目前的方法普遍存在测试时间较长、测试成本较高、所需样品体积较大或者检测限较高等问题。研究以低成本的膜进样质谱作为¹⁵N加富样品测试设备,建立了基于镉柱与氨基磺酸双还原体系测定¹⁵N加富样品中¹⁵NO₃^-含量的方法。经条件优化实验确定的具体方法:采用1mol/L HCl配制15mmol/L的氨基磺酸(SA)作为反应试剂除去样品原有的NO^-₂,然后利用镉柱将¹⁵NO₃^-还原为¹⁵NO^-₂,再按照1︰60(V︰V)的比例加入SA将¹⁵NO^-₂还原为²⁹N₂,最终被膜进样质谱检测。此方法可以测定的¹⁵NO₃^-样品浓度范围为0~40μmol/L,其精密度为0.3%(10μmol/L),并具备成本低、测定快速(3 min/样品)、样品消耗体积小、检测限低(0.05μmol/L)且无显著的盐效应等特点。利用该方法测得青岛石老人0~10cm砂质沉积物中¹⁵NH₄⁺和¹⁵NO^-₂的潜在氧化速率分别为0.08~0.17nmol N/(cm³·h)和0.53~1.56nmol N/(cm³·h),验证了研究所建立的方法适用于沉积物中硝化速率的测定。

关键词: sup>15N加富样品硝化氨基磺酸膜进样质谱

DOI：10.11693/hyhz20211000237

分类号:P734

基金项目:国家自然科学基金,U1806211号,42076035号,41606093号;中国海洋大学中央高校基本科研业务,202072001号。

附件

DETERMINATION OF ¹⁵NO^-₃ IN ¹⁵N-ENRICHED WATER SAMPLES BASED ON DOUBLE REDUCTION SYSTEM IN MEMBRANE INJECTION MASS SPECTROMETRY

LUO Chang^1,2,3, SONG Guo-Dong^1,2, LIU Su-Mei^1,2

1.Frontiers Science Center of 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

Abstract:

The nitrogen cycle in the ocean is one of the hot fields of marine biogeochemistry, and nitrification process is a key part of the nitrogen cycle. Accurate acquisition of nitrification rate is very important to understand marine nitrogen cycle. The¹⁵N labeled isotope technique is currently the most widely used method for determining the rate of nitrification in the world. The core of the method is to accurately determine the concentrations of ¹⁵NO^-₂ and/or ¹⁵NO₃^- in the ¹⁵N-enriched sample. However, the current methods generally have problems of long test time, high cost, large sample volume, and high detection limit. A robust and fast method was developed to determine the ¹⁵NO₃^- concentration in the ¹⁵N-enriched sample with the double reduction system of cadmium column reduction and sulfamic acid (SA). All the ¹⁵NO₃^- is converted to ²⁹N₂ and the ²⁹N₂ can be easily measured by membrane injection mass spectrometer (MIMS) with low cost and small volume. The specific method determined by the condition optimization experiment is: first, the 15 mmol/L SA (dissolved in 1 mol/L HCl) as the reaction reagent remove the original ¹⁵NO^-₂, ¹⁵NO₃^- is reduced by a cadmium column, and the 15 mmol/L SA (dissolved in 1 mol/L HCl) is added to the solution with a reagent: sample =1 : 60 (V/V). The produced ²⁹N₂ can be measured by MIMS, and the original concentration of ¹⁵NO₃^- can be derived from the signal of ²⁹N₂. The method has a detection limit of 0.05μmol/L for ¹⁵NO₃^-, a linear range of 0~40μmol/L, and a precision of 0.3% (at 10μmol/L), with no salt effect. The potential oxidation rates of ¹⁵NO⁺₄ and ¹⁵NO₂^- in the 0-10 cm layer of the sandy sediment of Qingdao Shilaoren were 0.08~0.17 nmol N/(cm³·h) and 0.53~1.56 nmol N/(cm³·h) with the method, respectively. The established method in this study can be applied to determine the potential rate of nitrification in sediments.

Key words: ¹⁵N enriched sample nitrification sulfamic acid membrane injection mass spectrometry