Separation of thiosulfate and the polythionates in gold thiosulfate leach solutions by capillary electrophoresis

A technique for the separation of thiosulfate (S2O32-), polythionates (SxO62-, x = 3 to 5) and the gold(I) thiosulfate complex (Au(S2O3)23-) using capillary electrophoresis with simultaneous UV detection at 195 and 214 nm is presented. The five species were separated in under 3 min with a total analysis time of 8 min, using an electrolyte containing 25 mM 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (bis-tris) adjusted to pH 6.0 with sulfuric acid and an applied voltage of -30 kV. While the gold(I) thiosulfate complex could be separated from the other analytes of interest under these conditions, the quantification of this complex was not possible due to inconsistent peak areas and peak splitting effects induced by the sulfur-oxygen species in the leach matrix. Detection limits calculated for 3s pressure injection at 50 mbar ranged between 0.5-2 M. The method was linear over the ranges 40-8000, 10-2000, 10-2000, and 5-2000 M for thiosulfate, trithionate, tetrathionate, and pentathionate, respectively. The technique was applied successfully to leach liquors containing 0.5 M ammonium thiosulfate, 2 M ammonia, 0.05 M copper sulfate and 20% w/v gold ore, diluted 1:100 prior to analysis.