LAUSR

Electrochemical determination of phosphate in aqueous solution attracts considerable interests in both biological and environmental fields. Due to the electrochemical inactive nature of phosphate, direct electrochemical detection of phosphate is still a highly challenging task. Herein we reported one direct electrochemical approach for the determination of phosphate based on the oxidation of coordinated OH during the phase transition of calcium phosphates (CaP). The mixture of amorphous calcium phosphate (ACP) and octacalcium phosphate (OCP, Ca8(HPO4)2(PO4)4•5H2O), which acts as the starting material for hydroxyapatite (Ca10(PO4)6(OH)2, HAP), was self-assembled on Nafion modified glassy carbon electrode (GCE). The as-prepared electrode (CaPs/Nafion) showed a distinct oxidation peak at 1.0 V vs Ag/AgCl in phosphate solution. The peak heights were directly proportional to the concentration of phosphate from 0.1 µM to 10 µM in the presence of 1 mM Ca2+. After comprehensive characterization of the CaPs/Nafion electrode, it was understood that phosphate ion as a proton acceptor could stimulate the generation of coordinated OH from coordinated water (H2O) in the CaP. The addition of Ca2+ could magnify the coordinated H2O source due to its hydration to H2O. The CaPs/Nafion electrode also displayed good selectivity as the electrochemical oxidization response was not affected by up to 10 µM of the potentially competitive species like CO32-, NO3-, CH3COO-, SO42-, Cl-. The results obtained in this work not only provided a new method for direct detection of phosphate in aqueous solution, but also suggested that Ca2+ could be a promoter for electrochemical oxygen generation.