An UV photo-oxidation technique was developed to establish a practical method for measuring the total dissolved organic matter in natural waters. By exposing to a 450 W high pressure mercury lamp, all of the organic nitrogen compounds have been oxidized to a mixture of nitrate and nitrite within three hours, while ammonium has been oxidized far more rapidly. Phosphorus compounds have also been converted to phosphate within two or three hours. An attempt of measuring the dissolved organic carbon by the combination of this technique and an infra-red CO₂ analyzer has failed because of high blanks of carbon dioxide. It has been found that the blanks can be minimized when helium gas is used in place of nitrogen to remove the carbon dioxide from the sample water prior to the UV irradiation. Some results of nitrogen and phosphorus determination by this technique have been obtained for samples of different types of natural waters.

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