| 摘要: |
| 铵态氮作为氮元素的一种重要存在形态，是水体污染状况的指标之一。鉴于目前铵态氮同位素测试方法都存在预处理过程复杂，转化率低，所需样品量大，检测效率低下，对测试NH+4浓度低的水样存在困难，本研究建立了次溴酸盐-盐酸羟胺转化法测试铵态氮同位素的方法，并应用于三种类型的水样（海水、河水和土壤浸提液）铵态氮同位素测试。通过测试铵态氮标准样品的氮同位素，确定该方法的转化率、精密度、准确度和检出限等指标，并建立铵态氮同位素校准曲线。实验结果显示，铵态氮标准溶液NH+4浓度范围2.5~50.0 μmol/L 之间，NH+4氧化还原为N2O的转化效率均大于90%，不同浓度δ15N(N2O)标准偏差均在0.5‰以内；4种丰度铵态氮同位素标样校准曲线斜率为0.489，相关系数R2为0.999，相关性良好，转化过程氮同位素未见分馏；水样中NH+4浓度的检出限为2.5 μmol/L。实测三种类型水样δ15N(NH+4)的标准偏差分别为0.18‰、0.27‰和0.30‰（n=5），与次溴酸盐叠氮化钠转化法测得δ15N(NH+4)的差值分别为-0.03‰、0.86‰和-0.95‰，表明两种方法测试结果差值在误差范围之内，其结果可相互验证。本转化法中用盐酸羟胺替代剧毒易爆的叠氮化钠试剂，对环境更友好，且具有更高的方法精密度和准确度，能够满足环境中不同类型水样铵态氮同位素分析测试要求。 |
| 关键词: 海洋化学 盐酸羟胺 次溴酸盐 氮同位素 铵态氮 前处理方法 |
| DOI：10.3969/J.ISSN.2095-4972.20240527001 |
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| 基金项目:中国地质调查局舟山海洋地质灾害野外科学观测研究站开放基金（ZSORS-22-10）；自然资源部第三海洋研究所基本科研业务费（海三科2024010，海三科2024014） |
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| Study and application of a method for testing nitrogen isotopes in ammonium salts by the hypobromite-hydroxylamine hydrochloride conversion method |
| CHEN Peiyu,YIN Xijie,YANG Haili |
| (Third Institute of Oceanography, MNR, Xiamen 361005, China) |
| Abstract: |
| Ammonium nitrogen, as an important form of nitrogen, is one of the indicators of water pollution. In view of the complexity of the pretreatment process, low conversion rate, large sample volume and low detection efficiency of the current ammonium nitrogen isotope testing methods, it is difficult to test water samples with low NH4+ concentration. A hypobromite-hydroxylamine hydrochloride conversion method for ammonium nitrogen isotope testing was established and applied to three types of water samples (seawater, river water and soil leachate) for ammonium nitrogen isotope testing. By testing the nitrogen isotopes of ammonium nitrogen standard samples, the conversion rate, precision, accuracy and detection limit of the method were determined and the ammonium nitrogen isotope calibration curve was established. Experimental results showed that the NH+4 concentration range of the ammonium nitrogen standard solution was 2.5~50.0 μmol/L, the conversion efficiency of NH+4 oxidative reduction to N2O was more than 90% and the standard deviations of δ15N(N2O) at different concentrations were within 0.5‰. The slopes of calibration curves of 4 abundance ammonium nitrogen isotope standard samples were 0.489 and the correlation coefficients R2 were 0.999, which showed a good correlation. The correlation coefficient R2 was 0.999 and the correlation coefficient was 0.999 with good correlation. The nitrogen isotopes were not fractionated during the transformation process. The detection limit of NH+4 concentration in water samples was 2.5 μmol/L. The standard deviations of δ15N(+4) in the three types of water samples were 0.18‰, 0.27‰, and 0.30‰, respectively (n=5). The differences with that of δ15N(+4) in the hypobromite-sodium azide transformation were -0.03‰ and -0.03‰, respectively (n=5) and the differences were -0.03‰, -0.03‰ and -0.05‰, respectively, for three types of water samples. The differences were -0.03‰, 0.86‰ and -0.95‰, respectively, indicating that the differences between the test results of the two methods were within the error range and their results could be verified with each other. The replacement of highly toxic and explosive sodium azide reagent with hydroxylamine hydrochloride in this conversion method is more environmental friendly and has higher precision and accuracy, which is able to meet the requirements of isotope analysis and testing of ammonium nitrogen in different types of water samples in the environment. |
| Key words: marine chemistry hydroxylamine hydrochloride hypobromate nitrogen isotope ammonium nitrogen Pre-treatment methods |
