Simultaneous potentiometric determination of ClO3--ClO2- and ClO3--HClO byflow injection analysis using Fe(III)-Fe(II) potential buffer

A rapid potentiometric flow injection technique for the simultaneous determ ination of oxychlorine species such as ClO3--ClO2- and ClO3--HClO has been developed, using both a redox electrode detector and a Fe(III)-Fe(II) poten tial 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 C lO2- obtained by the transient potential change were enhanced 700-800-fold over that using an equilibrium potential. The detection limit of the presen t method for HClO and ClO2- is as low as 5 x 10(-8) M with use of a 5 x 10( -4) M Fe(III)-1 x 10(-3) M Fe(II) buffer containing 0.3 M KCI and 0.5 M H2S O4. On the other hand, sensitivity to ClO3- was low when a potential buffer solution containing 0.5 M H2SO4 was used, but could be increased largely b y increasing the acidity of the potential buffer. The detection limit for C lO3- was 2 x 10(-6) M with the use of a 5 x 10(-4) M Fe(III)-1 x 10(-3) M F e(II) buffer containing 0.3 M KCI and 9 M H2SO4. By utilizing the differenc e in reactivity of oxychlorine species with chloride in the potential buffe r, a simultaneous determination method for a mixed solution of ClO3--ClO2- or ClO3--HClO was designed to detect, in a timely manner, a transient poten tial 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 x 10(-5)-2 x 10(-4) M for ClO3-, and 1 x 10(- 6)-1 x 10(-5) M for HClO and ClO2-. The reproducibility of the present meth od was in the range 1.5-2.3%. The reaction mechanism for the transient pote ntial change used in the present method is also discussed, based on the res ults of batchwise experiments. The simultaneous determination method was ap plied to the determination of oxychlorine species in a tap water sample, an d was found to provide an analytical result for HClO, which was in good agr eement with that obtained by the o-tolidine method and to provide a good re covery for ClO3- added to the sample. (C) 1999 Elsevier Science B.V. All ri ghts reserved.