Matrix-elimination ion chromatography with post-column reaction detection for the determination of iodide in saline waters

An ion chromatographic method has been developed for the determination of traces of iodide in saline waters. A Dionex IonPac AS11 anion-exchange column was used with a mobile phase containing sodium chloride in order to remove interferences of the sample matrix in both the chromatographic separation and detection. This matrix-elimination procedure was reinforced by a post-column reaction detection that was both selective and sensitive for iodide and was based on the reaction of iodide with 4,4′-bis(dimethylamino)diphenylmethane in the presence of N-chlorosuccinimide. Detection was carried out at 605 nm. The detection limit for iodide in seawater is at about 0.8 ppb for a 150-μl injection, and the relative standard deviation at 5 ppb is better than 4%. Bromide is a potential interference, but is well separated from iodide. No interferences from dissolved organic matter in natural samples have been observed.