DETERMINATION OF IODIDE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AFTER PRECOLUMN DERIVATIZATION

Derivatization of iodide into 4-iodo-2,6-dimethylphenol and HPLC of iodophenol with UV detection has been found to be a suitable method for the sensitive detection of iodide. The precolumn derivatization Involved oxidation of iodide with 2-iodosobenzoate at pH 6.4 in the presence of 2,6-dimethylphenol. The reaction mixture was chromatographed on an octadecylsilane column using a mobile phase of acetonitrile-water, 60:40 (v/v), and detection at 220 nm. With an injection volume of 100-mu-L, the detection limit was 0.5 ng of iodide. After complete reaction of iodide at pH 6.4, the solution was adjusted to pH 1 to effect the derivatization of bromide if it was also present with iodide. A mobile phase of acetonitrile-water, 45:55 (v/v), was used for the simultaneous determination of iodide and bromide. The detection limit for bromide was 0.2 ng. Methods have also been evolved for iodine (precolumn reaction without using 2-iodosobenzoate) and iodate (reduction with ascorbic acid to iodide and its derivatization) and for the analysis of iodide, iodine, and iodate in the presence of each other. Application of the method has been made to the determination of iodide in natural water, sea water, iodized salt, milk, and pharmaceuticals. The RSD was in the range 0.4-2.9%.