Determination of experimentally enriched15N in nitrate nitrogen based on an improved method of azo dye formation |
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| Authors: | Hideki Yakushiji Jota Kanda |
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| Institution: | (1) School of Science, Shizuoka University, 836 Ohya, 422-8529 Shizuoka, Japan;(2) Present address: Department of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, Hokkaido, Japan |
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| Abstract: | A method has been developed for determination of15N isotope ratio in nitrate nitrogen, which is a major analytical step in tracer experiments for studies of nitrate metabolism
in the marine environment. The method is based on diazotization of nitrite with sulfanilic acid following reduction of nitrate
to nitrite by a cadmium-copper column. The diazonium compound is then subject to the azo coupling reaction with 2-naphthol,
and the azo dye formed is extracted by a solid phase extraction column. The dye eluted from the column is collected, and total
nitrogen and15N content of the dye are determined by mass spectrometry. Sulfanilic acid can also remove preexisting nitrite by heating the
sample under acidic conditions before passing through the cadmium-copper reduction column. The average recovery of nitrate
nitrogen was 86%. A procedure for reducing the background nitrogen that derives from the analytical operations has been developed;
background nitrogen was limited to about 0.25 μg-atomN. The variation in the background nitrogen levels reflects the range of error in15N determination of nitrate nitrogen by this method. Application of the present method to a15NO3
− isotope dilution experiment for determination of nitrification rate in sea water is demonstrated. |
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| Keywords: | 15N nitrogen cycling nitrate nitrification isotope dilution nitrate reduction sulfanilic acid azo dye solid phase extraction |
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