Capillary electrophoretic determination of thiosulfate and its oxidation products

Capillary electrophoresis (CE) was developed for the rapid and simple determination of thiosulfate and its oxidation products such as common polythionates, sulfite and sulfate. Direct and indirect UV detection techniques were investigated. The optimized separations of UV absorbing S2O32−, S4O62−, S5O62− and S6O62− anions were carried out in 5 mmol l−1 (NH4)2SO4, 5 mmol l−1 KH2PO4 electrolyte at pH 5.0, with direct UV detection at 214 nm. All analytes were well resolved in less than 4 min. Analysis of S2O32−, S4O62−, SO42− and SO32− ions can be performed in 5 mmol l−1 H2CrO4, 1 mmol l−1 hexamethonium hydroxide electrolyte neutralized with triethanolamine to pH 8.0, using indirect UV detection at 254 nm. However, the detection sensitivity for tetrathionate was poor. Other polythionates can not be detected at all because of their high absorbance even at 254 nm. The developed CE method was applied for the monitoring of sulfur species in spent fixing solutions during the electrolytic oxidation.