Wet-oxidation and automated colorimetry for simultaneous determination of organic carbon, nitrogen and phosphorus dissolved in seawater

We developed a simple and reliable method which allows simultaneous determi nation of organic forms of carbon (DOC), nitrogen (DON) and phosphorus (DOP ) dissolved in seawater. Conversion of dissolved organic matter (DOM) to in organic products (carbon dioxide, nitrate + nitrite and soluble reactive ph osphate) is performed by a persulfate wet-oxidation in low alkaline conditi on, After oxidation, the concentration of the inorganic products dissolved in the sample was measured automatically by colorimetry using a 3-channel T echnicon AutoAnalyzer system. A number of pure organic compounds were teste d in the concentration range encountered in coastal and open ocean, indicat ing a high efficiency of the digestion procedure, The recovery range is sim ilar to that obtained by other wet-oxidation procedures and by high-tempera ture catalytic oxidation techniques. Direct comparisons with usual methods used for separate determination of DOG, DON and DOP indicated a high effici ency of the procedure. Reproducibility tests demonstrated a very good preci sion (around 5%) for lagoonal and coastal waters, while precision was somet imes around 10-25% in oligotrophic oceanic waters, especially for DOP where values approached limits of detection for measuring phosphate. This method is highly suitable for routine analysis and especially appropriate for shi pboard work. (C) 1999 Elsevier Science B.V. All rights reserved.