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 Fe^III and Ni^II chelates also gave peaks, but the Cu^II and Zn^II chelates did not. The calibration graph for Co^II was linear at the 10^–10 mol dm^–3 level after 25-fold preconcentration. The detection limit of Co^II was 1.1 × 10^–10 mol dm^–3.