This paper proposes an electrochemical method for phosphate determination with oxalic acid as masking agent to eliminate silicate interference in freshwater. An electrochemical cell including electrochemical threeelectrode system, reaction zone, inlet and outlet was designed and fabricated to detect phosphate by Sequential Injection Analysis (SIA). The influence of the masking agent and its concentration on the determination of phosphate were investigated. With 0.01% oxalic acid as masking agent, better signal amplitude and less signal distortion were displayed. The reason may be that the
oxalic acid replaces molybdosilicate easier than molybdophosphate. In this way, oxalic acid inhibits silicate interference and shows less influence on phosphate determination. The linear ranges of phosphate from 0 to 1.0 mg/L were displayed with oxalic acid as mask reagent in freshwater. For natural samples, the deviation between spectrophotometric and LSV methods is less than 10%. The experimental results indicated that the proposed method can be applied to in situ monitoring of phosphate.
Yu Song, Chao Bian, Yang Li, Jianhua Tong and Shanhong Xia