Linear sweep voltammetric determination of free chlorine in waters using graphite working electrodes

Abstract

Applicability of linear sweep voltammetry using graphite working electrodes for determination of free chlorine in waters was demonstrated. Influence of the nature of supporting electrolyte, its concentrations, pH and rate of potential variation of working electrode on voltammetric responses corresponding to the oxidation of CIO- were examined. It was found that, any of the salt solutions KNO3, K2SO4 or Na2 SO4 at the optimum concentration of 0.1 mol dm-3 could be used as a supporting electrolyte for the above determination. The study also revealed that, any pH in the range of 8.5 to 11 could yield satisfactory results. The anodic peak current at the working electrode potential of +1.030 VvsAg/AgCl reference electrode was found to linearly increase with concentration of free chlorine up to 300 mg dm-3 (R2 = 0.9996). The results indicated that the anodic peak current could be used as the basis for a simple, rapid and accurate detennination of CIO- in waters in the concentration range from 1.0 mg dm-3 to 300.0 mg dm-3 with a high degree of reproducibility (% RSD < 1.5). The results obtained with the proposed method for determination of concentrations of CIO- in commercial bleaching agents were in good agreement with those determined iodometrically (% difference <1.5). The method proved advantageous as it does not require purging of test solutions with nitrogen for removing of dissolved oxygen prior to voltammetric determinations. The applicability of square wave voltammetry in place of linear sweep voltammetry for determination of CIO- has also been demonstrated.