Spectrophotometric Determination of Iodine Species in Table Salt, Pharmaceutical Preparations and Sea Water

A sensitive spectrophotometric method for the determination of iodine species like iodide, iodine, iodate and periodate is described. The method involves the oxidation of hydroxylamine to nitrite with iodate under acidic condition. The formed nitrite is determined based on the diazo coupling reaction between p-nitroaniline and N-(1-naphthyl) ethylenediammine dihydrochloride [NEDA]. The method obeys Beer’s law in the concentration range 1-15 μg of iodate in an overall aqueous volume of 10 mL at 545 nm and the color is stable for 3h. The relative standard deviation is 1.7 % (n=10) at 12 mug of iodate. The molar absorptivity is calculated to be 8.33 x 10^4 L mol^-1cm^-1 with a correlation coefficient of 0.9998. The developed method can be applied to samples containing iodine and iodide by oxidation to iodate using bromine solution under acidic condition. Periodate is determined by prereduction to iodate using ethylene glycol under acidic condition. The optimum experimental reaction conditions are evaluated. The effect of interfering ions on the determination of iodate is described. The proposed method has been successfully applied to the determination of iodide and iodate in salt samples, iodine in pharmaceutical preparations and added periodate in sea water sample.