Ion chromatography for rapid and sensitive determination of inorganic sulfur anions in their mixtures

Abstract

Ion chromatographic methods were developed for the rapid separation and sensitive determination of trace sulfur anions in their mixtures : sulfide, sulfite, sulfate, thiosulfate, thiocyanate, dithionate and polythionates (tri-, tetra-, penta- and hexathionate) in water samples. The sulfur anions were resolved at short elution-times by: (1) ion-exchange chromatography, (2) ion-exclusion chromatography and (3) ion-pairing chromatography; (1) an anion-exchange column was used with an eluent of carbonate-1,3,5- benzenetricarboxylate (BTC), carbonate-acetonitrile and phthalate, (2) a column of cation exchanger of low crosslinking with diluted sulfuric acid mobile phase containing acetonitrile, and (3) a silica ODS column with acetonitrile-water mobile phase including tetra-n-propylammonium salt (TPA) of an ion-pairing reagent. The sulfur species in the effluent from the separating columns were measured by means of suppressed conductivity detection and UV photometry. Sensitive detection of the analyte, even when using phthalate eluent and carbonate eluent containing BTC, having strong eluting-power, was accomplished by a suppressed conductivity detection technique, because the benzenepolycarboxylate eluent ions could be converted to their acid forms of low conductivity on the suppressor. The sensitivity of determination of the sulfur anions was also increased by an indirect UV detection system using a postcolumn reaction, in which the residual iodine was measured as triiodide at 350 nm after reactions of the analytes (sulfide, sulfite and thiosulfate) with iodine, and iodine-azide reactions catalyzed by sulfide, thiosulfate, thiocyanate and polythionates (tri-, tetra-, penta- and hexathionate); their detection limits ranged from 10-7 to 10-6 M. Furthermore, a highly sensitive determination (detection limits of 10-8 M level) of thiosulfate, thiocyanate and four polythionates was achieved by the direct measurement of their absorbance at 230 nm, without any postcolumn reaction system. The proposed methods were successfully applied to the determination of sulfur anions of sulfide, sulfite, sulfate, thiosulfate and tetrathionate in hot-spring water samples. Their recoveries of thiosulfate and polythionates added to the water samples were also quantitative (96.0-104.3%). © 2005 The Japan Society for Analytical Chemistry.