Synthesis of 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol and its application to the spectrophotometric determination of cobalt.

2-(3,5-Dichloro-2-pyridylazo)-5-dimethylaminophenol (3,5-diCl-DMPAP) has been synthesized and its analytical application investigated. It reacts with cobalt in aqueous solution at pH 2.2-6.0 and room temperature to form a water-soluble ML(2) complex with absorption maximum at 590 nm, and molar absorptivity 8.4 x 10(4) l.mole(-1).cm(-1). Interference from other transition metals can be eliminated by their solvent extraction with 8-hydroxyquinoline. The method has been successfully applied to determination of cobalt in mild steels.