Selective spectrophotometric determination of cobalt( II ) using 2,2′-dipyridyl-2-pyridylhydrazone and a flow injection manifold

Micro-amounts of cobalt(II) were determined spectrophotometrically at 500 nm using a flow injection manifold and 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) as a colour-forming reagent. The various chemical and physical variables were optimized and a study of interfering ions was also carried out. A linear calibration graph was obtained for 0–12.0 mg l–1 cobalt(II), at a sampling rate of 90 injections per hour. The accuracy and reproducibility were very good (sr= 0.4%), the limit of detection was 0.017 mg l–1 and the limit of quantitation was 0.031 mg l–1. The method was found to be adequately selective owing to the fact that the strongly acidic medium used prevented the formation of complexes of the reagent with other ions. The method has been successfully applied to the determination of cobalt in cyanocobalamin (vitamin B12).