Determination of iodide by derivatization to 4-iodo-N,N-dimethylaniline and gas chromatography-mass spectrometry

A real-time determination of iodide is proposed which involves the oxidation of iodide with 2-iodosobenzoate in the presence of N,N-dimethylaniline. The reaction is completed within 1 min to yield 4-iodo-N,N-dimethylaniline, which is extracted in cyclohexane and determined by GC-MS. It was also possible to determine iodine by derivatization in the absence of 2-iodosobenzoate, and iodate by its reduction with ascorbic acid to iodide and subsequent derivatization. A rectilinear calibration graph was obtained for 0.02-50 micrograms l-1 iodide with a correlation coefficient of 0.9998. The limit of detection was 8 ng l-1 iodide. The method was applied to the determination of iodate in iodized table salt and free iodide and total iodine in sea-water, and to spiked samples when the recovery was in the range 96.8-104.3% (RSD 1.9-3.6%). A sample clean-up by solid-phase extraction with a LiChrolut EN cartridge is proposed.