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

A phosphate ion-selective electrode using molybdenum metal was constructed. The modified molybdenum electrode responded to HPO₄^2- in the presence of molybdenum dioxide and molybdophosphate (PMo₁₂O₄₀^3-) on the surface. The electrode exhibited a linear response to HPO₄^2- 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 HPO₄^2-, 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^-, SO₄^2-, 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.