Pretreatment with Photodecomposition for Speciation of Dissolved Phosphorus Compounds and Investigation on Their Photodecomposition Mechanism

Nishi Takashi, Hirayasu Takahiro, Kubono Koji, Yokoi Kunihiko

doi:10.2116/bunsekikagaku.59.659

A pretreatment method for the speciation of dissolved phosphorus compounds in water samples is proposed. For a sample solution containing orthophosphate, organophosphorus compound, and polyphosphoric acid, a three-step procedure has been developed for the determination of each phosphorus compound. At first, orthophosphate was determined with a conventional molybdenum-blue method. Second, an organophosphorus compound was decomposed selectively to orthophosphate by five minutes of UV irradiation with using a 400 W low-pressure mercury lamp. Finaly, in the presence of sulfuric acid and photocatalytic TiO₂, the organophosphorus compound and polyphosphoric acid were decomposed to orthophosphate by thirty-five minutes of UV irradiation. The orthophosphate concentration obtained for each step was successfully used to estimate the concentration of the orthophosphate, organophosphorus compound, and the polyphosphoric acid originally present. In addition, an investigation of the wavelength dependence of the decomposition efficiency with a colored glass filter, showed that the irradiation of 184.9 nm is important for photodecomposing an organophosphorus compound; that of 365 nm in the presence of photocatalytic TiO₂ is important to photodecompose polyphosphoric acid. This new method should be effective as a pretreatment method for the speciation of dissolved phosphorus compounds.

Pretreatment with Photodecomposition for Speciation of Dissolved Phosphorus Compounds and Investigation on Their Photodecomposition Mechanism

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