Study on Rapid Pretreatment Method with Cobalt (III) Ions for Speciation of phosphorus in Environmental Samples

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A pretreatment method of organic phosphorus based on cobalt (III) oxidation, was studied for spectrophotometric determination of phosphorus in environmental water samples ; cobalt (III) ions were produced through the electrolysis of an acidic solution of cobalt (II) sulfate. The pretreatment first examined in a batchwise mode and then applied to an on-line pretreatment in a system of flow injection analysis (FIA). The cobalt (III) pretreatment enabled complete conversion of mg dm^<-3> level of phosphorus of organic phosphorus compounds having C-O-P or C-P bond into phosphate ions within 7 min at room temperature with an aid of a platinum catalyst ; cobalt (III) ions from the reagent did not interfere with the subsequent determination of phosphate ions by the Molybdenum Blue method. Condensed phosphates required heating at 95-100ﾟC for complete hydrolysis during the pretreatment. The detection limit for phosphorus was 0.005 mg dm^<-3> and 10-12 samples could be determined per 1h (the FIA system). Since the present method was free from any interference from coexisting organic and inorganic substances, except at a relatively high level of reducing substances, it is applicable to the determination of organic or total phosphorus in real water samples.