Chemical Nature of Dissolved Organic Matters in Sea Water

Abstract

By employment of coprecipitation technique with ferric hydroxide, soluble organic matters were isolated from the surface sea water collected from the Inland Sea of Japan to examine the chemical nature of these isolated substances.
44% of the dissolved organic matters coprecipitated with ferric hydroxide. The coprecipitates were fractionated into acidic, neutral, basic and humic substances by the method shown in Fig. 2. Carbon Nitrogen ratio of these fractionated substances amounted to 8. Gel filtration profiles of the organic substances indicated that 50% of the isolated organic substances had molecular weight below 1,500, while 21% had over 10,000 molecular weights, as compared with dextran. These facts suggested that the organic matters isolated by coprecipitation had less molecule, containing more nitrogen than those obtained by dialysis from sea water and by vacuum evaporation from fresh water.
Infra red spectra were examined on all the fractionated substances, and the absorption patters were shown in Fig. 4. The absorption bands at 3,400, 1,640 and 1,410 cm^-1 implied the presence of alcoholic or phenolic hydroxyl group, doubly bound carbon atoms in conjugated phenyl groups and alkan groups. The absorption at 1,700 cm^-1 of acidic fraction showed the presence of the carboxyl groups.
Paper electrophoresis was used for purification of the organic substances. Acidic and neutral fraction was detected with potassium permanganate to be a continuous spot lying across the original line. Fluorescent spot was found to be on the cathod side by use of ultraviolet light. Basic fraction was developed mainly on the anode side (Fig. 5).
The fractionated substances by ion-exchange resins showed a peculiar band of fluorescence centering between 393 and 460 nm with the wavelength of maximum excitation located in the region of 313-385 nm.