Modified Method for the Analysis of Nitrogen Isotopic Composition of Oceanic Nitrate at Low Concentration
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- 作者：Tomoyuki Tanaka and Toshiro Saino
- 关键词：Isotope analysis ; nitrogen isotope ; oceanic nitrate
- 刊名：Journal of Oceanography
- 出版年：2002
- 出版时间：2002
- 年：2002
- 卷：58
- 期：4
- 页码：539-546
- 全文大小：1.11 MB
文摘
A method for the determination of the δ15N of nitrate in seawater described by Cline and Kaplan (1975) has been modified for application to low-level nitrate samples. We have minimized the reagent blank problem by replacing the Devarda's alloy with an aluminum reagent, and have also established a procedure that yields quantitative (93 ¡À 2 % ) extraction of nitrogen even at low nitrate levels. Though the amounts and the δ15N of the blank N varied from one reagent set to another, with these modifications, an overall N blank was reduced to approximately 0.80 ¡À 0.33 ¦Ìmole N having an estimated δ15N value of −1.8‰. After blank and yield corrections, the measured isotopic composition of nitrate differed by approximately 0.1‰ from the actual value while the precision was within ¡À0.2‰ at the 1.25 ¦ÌM level. The modified procedure was applied to seawater samples collected from the equatorial Pacific in order to compare the N blanks in field samples with those derived from laboratory experiments. The results support the suitability of the modified approach for isotopic analysis of oceanic nitrate in shallow water.