Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater

YANG Zhi; CHEN Min; CAO Jianping; QIU Yusheng

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YANG Zhi, CHEN Min, CAO Jianping, QIU Yusheng. Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater[J]. Haiyang Xuebao, 2012, 34(3): 72-79.

Citation:

YANG Zhi, CHEN Min, CAO Jianping, QIU Yusheng. Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater[J]. Haiyang Xuebao, 2012, 34(3): 72-79.

YANG Zhi, CHEN Min, CAO Jianping, QIU Yusheng. Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater[J]. Haiyang Xuebao, 2012, 34(3): 72-79.

Citation:

YANG Zhi, CHEN Min, CAO Jianping, QIU Yusheng. Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater[J]. Haiyang Xuebao, 2012, 34(3): 72-79.

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Ammonia distillation method for nitrogen isotope analysis of nitrate in seawater

1.
Department of Oceanography, Xiamen University, Xiamen 361005, China
2.
Department of Oceanography, Xiamen University, Xiamen 361005, China;State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, China

Received Date: 2011-09-06
Rev Recd Date: 2011-10-19

Abstract

Abstract

A distillation method for determining ¹⁵N abundance of nitrate in seawater was set up in this study.The method mainly involved the conversion of nitrate to ammonia using Devarda's alloy and the trapping of the ammonia with diluted HCl.After drying,nitrogen isotopic composition of the ammonium salts was measured by an isotopic ratio mass spectrometer.In this study,the amount of Devarda's alloy for nitrate reduction and the conditions for ammonium salts drying were assessed.A total of 3.0 g of Devarda's alloy was needed to completely reduce nitrate to ammonia in 2 dm³ seawater,and the drying of ammonium salts at 60 ℃ was appropriate for sample preparation for isotopic measurements.The overall nitrogen blank of our method was (0.90±0.19)μmol,and lower than those reported previously.The δ¹⁵N value of nitrogen blank was( -14.7±4.1)×10^-3.Nitrogen isotopic composition determined by this method was well consistent with that measured by the ammonia diffusion method,demonstrating the reliability of this method.The ammonia distillation method was applicable for measurement of nitrogen isotopes in seawater with the nitrate concentration of 2~50 μmol/dm³.The precision for nitrogen isotope determination was within ±0.3×10^-3.
- Nitrogen isotopes of nitrate,
- seawater,
- ammonia distillation method

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