Spectrophotometric method for the determination of iodate using methylene blue as a chromogenic reagent

A simple, rapid and sensitive spectrophotometric; method has been developed for the determination of iodate (IO3(-)) in table salt and sea water. The proposed method is based on the reaction of iodate with potassium iodide in an acid medium to liberate iodine. The liberated iodine bleaches the blue color of methylene blue and is measured at 665.6 nm. This decrease in absorbance is directly proportional to the iodate concentration and obeys Beer's law in the range of 0.5-14 mu gmL(-1) of IO3-. The molar absorptivity, Sandell's sensitivity, detection limit and quantitation limit of the method were found to be 1.24 x 10(4) Lmol(-1)cm(-1), 1.41 x 10(-2) mu gcm(-2), 0.048 mu gmL(-1) and 0.145 mu gmL(-1), respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination has been described. The proposed method has been successfully applied to the determination of the iodate in the table salt and sea water.