Kinetic spectrophotometric determination of iron(II) based on its inhibitory effect on the oxidation of methylthymol blue by bromate

A simple and sensitive kinetic-spectrophotometric method has been described for the determination of trace amounts of iron(II). The proposed method is based on the inhibitory effect of iron(II) on the oxidation of methylthymol blue by bromate in the sulfuric acid media and at 35 C, which was monitored at 440 nm. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. Iron(II) can be measured in the range of 1.0-200.0 ng/mL with a detection limit of 0.6 ng/mL. The relative standard deviations for ten replicate analysis of 50 and 160 ng/mL of Fe(II) were obtained 1.2% and 2.0 %, respectively. The method was found to be relatively selective in the presence of foreign ions. The developed method Was successfully applied to the determination of iron(II) in pharmaceutical products and real water samples.