Selective determination of cobalt in a strongly acidic medium by flow injection analysis

Summary A selective method for the FIA spectrophotometric determination of Co(II) based on the use of pyridoxal 4-phenylthiosemicarbazone as reagent was developed with the aid of a straightforward 4-line flow injection manifold. The physical variables involved in the process were optimized as follows: injected sample volume 260 l; reactor lengths 116 and 150 cm. The proposed method allows the determination of cobalt over the concentration range 0.4–14.4 g ml^–1 at a sampling rate of 48 samples h^–1. The method is subject to very few interferences thanks to the fact that the strongly acidic medium used prevents the formation of most of the complexes of the reagent with other ions. It was applied to the determination of cobalt in steels.