High-performance liquid chromatographic determination of cobalt(II) as the 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol chelate after preconcentration with a cation-exchange resin

Abstract

A preconcentration method with a cation-exchange resin for the high-performance liquid chromatography of the cobalt–2-(5-bromo-2-pyridylazo)-5-diethylaminophenol chelate was developed. The chelate was quantitatively adsorbed on sulfonated XAD-4 resin and eluted with a solution containing 0.1 mol dm–3 tetramethylammonium bromide, with a concentration factor of 50-fold. The chelate was then selectively separated on an ODS column with methanol–water (80 + 20 m/m) containing 2.0 × 10–3 mol kg–1 tetrabutylammonium bromide, 1.0 × 10–4 mol kg–1 ethylenediaminetetraacetic acid and 2.0 × 10–3 mol kg–1 acetate buffer (pH 5.0) as eluent. The FeIII and NiII chelates also gave peaks, but the CuII and ZnII chelates did not. The calibration graph for CoII was linear at the 10–10 mol dm–3 level after 25-fold preconcentration. The detection limit of CoII was 1.1 × 10–10 mol dm–3.