Simultaneous potentiometric determination of ClO 3−–ClO 2− and ClO 3−–HClO by flow injection analysis using Fe(III)–Fe(II) potential buffer

Abstract

A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO 3 −–ClO 2 − and ClO 3 −–HClO has been developed, using both a redox electrode detector and a Fe(III)–Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO 2 − obtained by the transient potential change were enhanced 700–800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO 2 − is as low as 5×10 −8 M with use of a 5×10 −4 M Fe(III)–1×10 −3 M Fe(II) buffer containing 0.3 M KCl and 0.5 M H 2SO 4. On the other hand, sensitivity to ClO 3 − was low when a potential buffer solution containing 0.5 M H 2SO 4 was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO 3 − was 2×10 −6 M with the use of a 5×10 −4 M Fe(III)–1×10 −3 M Fe(II) buffer containing 0.3 M KCl and 9 M H 2SO 4. By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO 3 −–ClO 2 − or ClO 3 −–HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2×10 −5–2×10 −4 M for ClO 3 −, and 1×10 −6–1×10 −5 M for HClO and ClO 2 −. The reproducibility of the present method was in the range 1.5–2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO 3 − added to the sample.