Flow injection atomic absorption spectrometric determination of iodide using an on-line preconcentration technique

A continuous flow atomic absorption spectrometric system was used to develop an efficient on-line preconcentration-elution procedure for the determination of iodide traces. Chromium (VI) is introduced into the flow system and is reduced to chromium (III) in acid medium proportionally to the iodide present in the sample. The Cr(III) reduced by iodide is retained on a minicolumn packed with a poly(aminophosphonic acid) chelating resin, while unreduced Cr(VI) is not retained. Reduced Cr(III) is preconcentrated by passing the sample containing iodide through the system during 3 min, and is then eluted with 0.5 mol L(-1) hydrochloric acid and determined by flame atomic absorption spectrometry (FAAS). The detection limit (3sigma) obtained is 2.5 microg L(-1). Other ions typically present in waters do not interfere. The proposed method allows the determination of iodide in the range 6-220 microg L(-1) with a relative standard deviation of 2.7% at a rate of 17 samples h(-1). The method has been applied to the determination of iodide in tap and sea waters.