ION-CHROMATOGRAPHIC DETERMINATION OF SULFIDE, SULFITE AND THIOSULFATE IN MIXTURES BY MEANS OF THEIR POSTCOLUMN REACTIONS WITH IODINE

The proposed method is based on the separation of sulfide, sulfite and thiosulfate in mixtures by using a resin-based anion-exchange column and a 5 x 10(-3) M (M=mol dm-3) sodium carbonate eluent, followed by a photometric measurement of any excess iodine (as triiodide) for its postcolumn reactions with the separated sulfur species. A postcolumn solution comprising 2.5 x 10(-5) M iodine, 0.01 M iodide and 0.8 M acetic acid was continuously mixed with an effluent from the separating columns and then the absorbance for the remaining iodine (as triiodide) in the stream was monitored at 330 nm. The chromatograms obtained for sulfide, sulfite and thiosulfate ions showed negative peaks, respectively, with detection limits (as S/N=2) of 2.09 x 10(-6) M(0.0669 ppm) for sulfide, 1.80 x 10(-6) M (0.144 ppm) for sulfite and 3.52 x 10(-6) M (0.394 ppm) for thiosulfate. The method was successfully applied to the determination of sulfide, sulfite and thiosulfate in hot-spring water samples.