Determination of Phosphorus Based on the Formation of a Reduced Keggin-Type 12-Molybdophosphate Complex in an Aqueous-Organic Solution

Abstract

A very simple, easy and sensitive spectrophotometric manual determination method of phosphorus for the PO₄^3- ion, based on the formation of the reduced 12-molybdophosphate complex, was developed. The effect of the kind of water-miscible organic solvent and the concentration of organic solvent, ascorbic acid and HCl on the formation of the complex was investigated. The optimum determination condition was confirmed based on these results. In an aqueous-CH₃CN solution, a P-PO₄^3- of 0.01 - 20 mg l^-1 could thus be determined. It was noted that the determination range of this study was wider than that of the phosphoantimonylmolybdenum blue method (0.032 - 1 mg l^-1). The effect of foreign ions on the absorbance was examined. The P-PO₄^3- in river water and seawater sampled in Kochi was determined by this method. The results were also compared with those of the phosphoantimonylmolybdenum blue method and capillary electrophoresis with an indirect detection method using K₂CrO₄.