MATRIX-ELIMINATION ION CHROMATOGRAPHY WITH POSTCOLUMN 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-exch ange column was used with a mobile phase containing sodium chloride in order to remove interferences of the sample matrix in both the chroma tographic separation and detection. This matrix-elimination procedure was reinforced by a post-column reaction detection that was both selec tive and sensitive for iodide and was based on the reaction of iodide with 4,4'-bis(dimethylamino)diphenylmethane in the presence of N-chlor osuccinimide. Detection was carried out at 605 nm. The detection limit for iodide in seawater is at about 0.8 ppb for a 150-mu l injection, and the relative standard deviation at 5 ppb is better than 4%. Bromid e is a potential interference, but is well separated from iodide. No i nterferences from dissolved organic matter in natural samples have bee n observed.