Development of a Differential Normal Pulse Voltammetric Method with a Plain Glassy Carbon Electrode for Determination of Phosphate in Water

This study aimed at developing a voltammetry-based method sensitive to interferences. Phosphate ion when reacted with molybdate forms an electroactive phosphomolybdate complex. Differential Normal Pulse Voltammetry (DNPV) and Cyclic Voltammetry (CV) techniques were used to assess the complex. Analysis by CV gave two redox centres with redox potentials of 0.167 +/- 0.02 V and 0.357 +/- 0.02 V, diffusion coefficients (D) of 1.408x10(-4) cm(2) s(-1) and 5.629x10(-7) cm(2) s(-1). Analysis by DNPV also gave two responses with potentials of 0.02 +/- 0.001 V and 0.33 +/- 0.001 V. DNPV response increased with phosphate concentration. The Linear Concentration Range (LCR) was found to be 0 to 8 mg/L, Limit of Detection (LOD) of 0.06586 mg/L, Limit of Quantitation (LOQ) of 0.21952 mg/L. The method had an accuracy range of 89%-102% and a precision of 7.93%. The method was evaluated using fifty water samples randomly collected from Lake Naivasha, Kenya. The mean phosphate concentration was 0.6156 +/- 0.1046 mg/L (at 95% Confidence Level). The study, therefore, showed that the DNPV method developed could be applied to the determination of phosphates in water at low levels.