Selective spectrophotometric determination of cobalt(II) in synthetic mixtures and pharmaceutical formulates with 5-[o-carboxyphenylazo]2,4-dihydroxybenzoic acid

The present work describes a selective, rapid and economical method for the determination of cobalt(II) using 5-[o-carboxyphenylazo] 2,4-dihydroxybenzoic acid [CPDB] as a spectrophotometric reagent without heating or extraction. The CPDB reacts with Co(II) in presence of Tween 80 surfactant forming a pink complex of a stoichiometric ratio 1:2 absorbed maximally at 555 nm with stability constant amounting to 10.33. Beer's law is obeyed for a concentration of at least 3.50 mug ml(-1) with Sandell sensitivity of 3.6 ng cm(-2) and molar absorptivity of 1.64 x 10(4) 1 mol(-1)cm(-1). The relative standard deviation for six replicate sample of 2.0 mug ml(-1) is 1.11%. A selective procedure is proposed for cobalt deter mination in presence of different metal ions in synthetic mixtures and in pharmaceutical formulations with more accurate results.