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

A preconcentration method with a cation-exchange resin for the high-pe rformance liquid chromatography of the cobalt-2-(5-bromo-2-pyridylazo) -5-diethylaminophenol chelate was developed. The chelate was quantita tively adsorbed on sulfonated XAD-4 resin and elated with a solution c ontaining 0.1 mol dm(-3) tetramethylammonium bromide, with a concentra tion factor of 50-fold. The chelate was then selectively separated on an ODS column with methanol-water (80. 20 m/m) containing 2.0 X 10(-3) mol kg(-1) tetrabutylammonium bromide, 1.0 X 10(-4) mol kg(-1) ethyle nediaminetetraacetic acid and 2.0 x 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 preconcentrat ion. The detection limit of Co-II was 1.1 X 10(-10) mol dm(-3).