1982 Volume 31 Issue 9 Pages 532-534
In the spectrophotometric determination of dissolved organic phosphorus in sea water by the heteropoly-blue method, the dissolved organic phosphorus is usually oxidised into inorganic phosphate by potassium persulfate prior to the determination. However, for the oxidation of the dissolved organic phosphorus in anoxic waters occurring in the lake Hamana, it was confirmed. in our experiments that the potassium persulfate method was not effective because of a reducing atomosphere in the anoxic waters. In the present work, following procedure by the use of a mixture of conc. HNO3 and HClO3 which is a stroger oxidising reagent than the above was established for the preliminary oxidation and the determination of the dissolved organic phosphorus under such conditions was made as follows. Twenty ml of a sample solution is heated with each five ml of conc. nitric and conc. perchloric acid on a hot plate until dryness. After cooling to room temperature, ten ml of water and one ml of 5 N sulfuric acid is added and residue is dissolved. The solution is transferred into a 25 ml volumetric flask with water, and the blue color of phosphorus-heteropoly blue is developed by addition of 4 ml the color-producing solution containing ammonium molybdate, ascorbic acid, and some others. The absorbance is measured at 867 nm using a 5 cm cell. The proposed method is particularly applied for to determination of microamounts of phosphorus (P≥1 ppb) in the anoxic waters occurring in bay.
