Ion-pair chromatography of polythionates and thiosulfate with detection based on their catalytic effects on the postcolumn azide-iodine reaction

The reduction of iodine with azide, catalyzed by polythionates (tri-, tetra -, penta- and hexathionate) and thiosulfate, has been utilized as a postcol umn reaction for chromatographic determination of these sulfur oxyanions. T he method is based on the separation of polythionates and thiosulfate on an octadecylsilica column with an acetonitrile-water (20:80, v/v) mobile phas e (pH 5.0) containing 3 mM tetrapropylammonium hydroxide and 6 mM acetic ac id, followed by photometric measurement of the residual iodine (as triiodid e) from the catalytic postcolumn azide-iodine reaction after mixing a react ion solution containing azide and iodine with the column effluent. Chromato grams obtained for the sulfur oxyanions showed negative peaks as a result o f the decrease in absorbance of background. The conditions for the catalyti c postcolumn reaction of the sulfur oxyanions in the column effluents were established by varying the concentrations of azide, iodine, iodide and acet ic acid in the reaction solution, and varying the flow-rate, reaction tempe rature and length of the reaction tube. The detection limits (defined as S/ N = 3) were 4.3 muM for trithionate, 0.10 muM for tetrathionate, 2.7 nM for pentathionate, 5.0 nM for hexathionate and 1.1 nM for thiosulfate. When co mpared with earlier methods, the proposed method gave a much higher sensiti vity for the determination of two polythionates (penta- and hexathionate) a nd thiosulfate. This method was applied successfully to the analysis of pol ythionates and thiosulfate added to hot-spring water samples. (C) 2001 Else vier Science B.V. All rights reserved.