Potentiometric flow injection analysis of trace bromate based on its redox-reaction with the iron(III)-iron(II) buffer solution containing bromide.

A rapid and highly sensitive method for the determination of bromate ion has been developed by applying to potentiometric detection of the flow injection technique (FIA). The method was based on the transient change of the potential in the redox-reaction of bromate ion with the iron(III)-iron(II) potential buffer solution containing bromide ion and sulfuric acid. The sample solution (140 mm³) injected into a carrier water stream is, at a confluence point, merged with the stream of the buffer solution containing sulfuric acid (1.2 mol dm^-3), sodium bromide (0.4 mol dm^-3) and the iron(III)-iron(II) (0.01 mol dm^-3). The reaction takes place during flowing of the sample zone through the reaction tube to the flow-through type ORP electrode detector. The potential change is observed as a peak-shaped signal. A linear relationship between the peak height and concentration of bromate ion was observed in the range of 1 × 10^-6 to 5 × 10^-6 mol dm^-3. At the sampling rate of ca. 40 samples per hour, the relative standard deviation was 0.98% (n=9) for the determination of 3 × 10^-6 mol dm^-3 bromate ion. Chloride, sulfate, nitrate and phosphate ions in 1000 times excess to bromate did not interfere with the determination of bromate ion.