A catalytic oxidation method for the determination of total nitrogen dissolved in seawater |
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| Authors: | Yoshimi Suzuki Yukio Sugimura Tadamasa Itoh |
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| Institution: | Geochemical Laboratory, Meteorological Research Institute, Nagamine 1-1, Yatabe, Tsukuba, Ibaraki 305 Japan;R & D Division, Sumitomo Chemical Industry Co. Ltd., Tsukahara 2-40, Takatsuki, Osaka 569 Japan |
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| Abstract: | A detailed examination of a high-temperature catalytic oxidation method for liquid samples in the analysis of total nitrogen dissolved in seawater is reported. The nitrogenous compounds in liquid samples are oxidized on a platinum catalyzer at 680°C under oxygen atmosphere and the generated NO2 is absorbed into a chromogenic reagent, followed by a spectrophotometric determination. The results of this method are much higher than those of wet oxidation methods. Molecular size dependency of the results clearly indicates that the above discrepancy is caused by the low oxidation capacity of the wet oxidation method against high-polymer organic matter dissolved in seawater. The results revealed that the concentration of total nitrogen in seawater is nearly constant from surface to bottom, ranging from 30 to 40 μM 1?1, which organic nitrogen concentration higher in the surface layer, and a rapid decrease with depth. An examination of molecular size distribution indicates that the concentration of high-polymer organic nitrogen decreases rapidly from surface to deeper layers, with molecular sizes ranging from 5 × 103 to 3 × 104. Because of the well-defined principle of the oxidation process, its reliability, ease of sample handling and of analytical procedure on board or in the land laboratory, the present method is much more suitable for the marine analytical chemistry of total and organic nitrogen than the other previous methods. |
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