Interference study on a continuous-flow determination system for sulphate with a lead-selective electrode detector and its application to natural water analysis

Abstract

In the continuous-flow determination of sulphate with a lead(II) nitrate reagent solution by using a lead-selective electrode as a potentiometric detector, the interference from hydrogen carbonate, chloride, calcium, nitrate and phosphate was examined in various compositions of the reagent solution. Positive interference from hydrogen carbonate was observed even in the presence of an acidic buffer. An anomalous concentration-dependent chloride interference was interpreted in relation to the dynamic response of the lead-selective electrode in the presence of chloride. The optimised composition of the reagent solution is 1 × 10^–5 or 5 × 10^–5M lead nitrate – 1 × 10^–3M monochloroacetic acid – 1 × 10^–2M sodium perchlorate in ethanol for rain and river water analysis, respectively. At the optimum lead ion concentration, continuous determination of sulphate in river and rain water was successfully carried out.