Results and observations from the measurement of DOC and DON in seawater using a high-temperature catalytic oxidation technique

Operating temperatures for the high-temperature catalytic oxidation of dissolved organic matter (DOM) in seawater were evaluated for optimization of total dissolved nitrogen analysis. In addition, the possibility of NO₂ being produced upon combustion, a gas not seen by the detector used here, was explored. Finally, some concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in coastal waters are reported. NO was most efficiently passed through the combustion furnace at temperatures 40°C or more above the 680°C temperature recommended earlier for DOM analysis. NO₂ was apparently not an important product of combustion, as an NO₂ calibration gas was efficiently converted to NO in the furnace and because the addition of a ferrous sulfate NO₂ converter did not result in significant increases in the detector response. DOC and DON concentrations were determined in seawater collected from three coastal sites-Santa Monica Basin and Monterey Bay in California and the Bering Sea inner shelf. The highest near-surface concentration of DOC reported here (123μM at 20 m) was found in Monterey Bay, and the lowest value (72 μM at 20m) was found in the Bering Sea. The highest DON concentration found in the surface 50 m was 6.0 μM in Santa Monica Basin.