Analytical Sciences

Fabrication of a Phosphate Ion Selective Electrode Based on Modified Molybdenum Metal

Kebin XU,* Yuki KITAZUMI,* Kenji KANO,* Takayuki SASAKI,** and Osamu SHIRAI*

*Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo, Kyoto 606-8502, Japan
**Department of Nuclear Engineering, Graduate School of Engineering and Faculty of Engineering, Kyoto University, Nishikyo, Kyoto 615-8530, Japan

A phosphate ion-selective electrode using molybdenum metal was constructed. The modified molybdenum electrode responded to HPO₄²⁻ in the presence of molybdenum dioxide and molybdophosphate (PMo₁₂O₄₀³⁻) on the surface. The electrode exhibited a linear response to HPO₄²⁻ in the concentration range between 1.0 × 10⁻⁵ and 1.0 × 10⁻¹ M (mol dm⁻³) in the pH range from 8.0 to 9.5 with a detection limit of 1.0 × 10⁻⁶ M. The sensor showed near Nernstian characteristics (27.8 ± 0.5 mV dec⁻¹) at pH 9.0. Since the responding potential was attributed to the activity of HPO₄²⁻, the potential at a given concentration of phosphate depended on the pH. The electrode indicated a good selectivity with respect to other common anions such as NO₃⁻, SO₄²⁻, Cl⁻, HCO₃⁻ and CH₃COO⁻. The modified molybdenum electrode can be continuously used for over a 1 month with good reproducibility. The feasibility of the electrochemical sensor was proved by successful for the detection of phosphate in real samples.

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