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-pyridylhyd razone (DPPH) as a colour-forming reagent, The various chemical and ph ysical variables were optimized and a study of interfering ions was al so 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 ac curacy and reproducibility were very good (s(r) = 0.4%), the limit of detection was 0.017 mg l(-1) and the Limit of quantitation was 0.031 m g l(-1). The method was found to be adequately selective owing to the fact that the strongly acidic medium used prevented the formation of c omplexes of the reagent with other ions. The method has been successfu lly applied to the determination of cobalt in cyanocobalamin (vitamin B-12).