Sensitivity enchancement by potentiometric flow-injection analysis based on redox reaction with an iron(III)-iron(II) buffer

Highly sensitive potentiometric flow-injection analysis for oxidative species such as bromate, chlorite, dichromate, hydrogen peroxide and ozone is described, using an Fe(III)-Fe(II) potential buffer continuing bromide. The method is based on detection of large transient potential changes of an oxidation-reduction potential electrode which appear in short period after mixing a sample with the potential buffer. This large transient potential change is due to bromine generated by the reaction of the sample with bromide in the potential buffer. Analytical sensitivities obtained by the transient change of potential are enhanced 25-350-fold compared with that using the change in equilibrium potential. Detection limits of 5 × 10^-8 M for bromate, 1 × 10 ^-7 M for chlorite and 3 × 10^-7 M for dichromate were obtained by using a 0.01 M Fe (III)-0.01 M Fe (II) potential buffer containing 0.4 M NaBr and 1.2 M H₂SO₄. For the determination of hydrogen peroxide, the addition of ammonium molybdate to the potential buffer accelerates the generation of bromine caused by the reaction of hydrogen with bromide and thus enhances the sensitivity.