Analytical Sciences

Laser-Heating Thermal Modulation Voltammetric Determination of Phosphate Ion Using a Graphite-Reinforced Carbon Electrode

Shovon Mohammad SHARIAR, Mizuki SUGA, Yumiko NISHIKAWA, and Teruo HINOUE

Department of Chemistry, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto 390-8621, Japan

Thermal modulation (TM) voltammetry was successfully applied to the determination of phosphate ion in natural water, by using a He-Cd dual laser as a heating source and a graphite-reinforced carbon (GRC) electrode. A heteropoly ion, i.e., 12-molybdophosphate ion ([PMo^VI₁₂O₄₀]^3-), was formed through a reaction between a phosphate ion and molybdate ions in an acidic solution, and its electroreduction was examined in a flow electrolytic cell by TM voltammetry. Measured TM voltammograms showed two peaks corresponding to two successive two-electron reductions of the 12-molybdophosphate ion, and the peak intensities were proportional to the concentration of the phosphate ion. Because of the strong adsorption of 12-molybdophosphate ion onto the GRC electrode, a detection limit as low as 0.8 nmol dm^-3 (S/N = 3) was achieved. The determination of phosphate ion in real samples (river water) was carried out by spectrophotometry (the molybdenum-blue method) and TM voltammetry, and the determination values obtained by both methods were in a good agreement with each other. These results prove the possibility of TM voltammetry as an electroanalytical method.

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