Determination of trace amounts of cobalt(II) by thin-layer spectrophotometry after enrichment on a membrane filter as the PAN complex

Abstract

A simple, selective and sensitive method for the determination of trace amounts of cobalt(II) has been developed. The method is based on the fixation of cobalt as the 1-(2-pyridylazo)-2-naphthol complex on a membrane filter and the direct determination of the reflection absorbance of the complex by densitometry. The working range of the calibration graph was 0.05–0.5 µg of cobalt(II). The recovery of cobalt(II) was not affected by the volume of sample solution up to 300 ml. The ligand buffer solution, composed of ethylenediaminetetraacetic acid and an excess of zinc(II), was found to be effective for masking interferences from foreign cations, especially from iron(III). The method was applied to the determination of cobalt(II) in white wine. The concentration of cobalt(II) found in four different wine samples was in the range 2.5–4.4 µg l^–1.