Analytical Sciences

Spectrophotometric Determination of Phosphate Anion Based on the Formation of Molybdophosphate in Ethylene Glycol–Water Mixed Solution

Hajime KATANO* and Tadaharu UEDA**

*Faculty of Biotechnology, Fukui Prefectural University, Eiheiji, Fukui 910-1195, Japan
**Faculty of Science, Kochi University, Akebono, Kochi 780-8520, Japan

New appropriate reaction system was found for spectrophotometric determination of phosphate anion. This spectrophotometric method is based on the color development due to the formation of yellow molybdophosphate anion in acidic ethylene glycol–water (EG-W) mixed solution containing Mo(VI) species. The solution containing e.g. 20 mM Na₂MoO₄, 0.1 M HCl, and 40% (v/v) EG is colorless, and becomes immediately yellow by addition of phosphate anion. Thus the method is simple, rapid, and easy to carry out. Although Si(IV) species is well known to interfere with the determination of phosphate anion in many cases, the EG-W Mo(VI) solution remains colorless after addition of silicate anion at 1 mM level, indicating that no yellow molybdosilicate anion was formed in the EG-W solution. Under an optimized condition, the absorbance at e.g. 400 nm of the EG-W P(V)-Mo(VI) solution was proportional to the concentration of phosphate anion with good reproducibility, and the detection limit was 1 μM. Also the present method is less interfered by high concentrations of potassium and ammonium cations and oxidative nitrite anion as well as silicate anion.

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