The micellar color reaction of cobalt with 2-(2-thiazolylazo)-5-dimethylaminobenzoic acid (TAMB) in the presence of nonionic surfactant was investigated. The pH range for the complex formation is within 3.8-5.8; the complex is stable in 2 mol. dm-3 HCl. The complex shows an absorption max. at 668 nm with apparent molar absorptivity of 1.22 ?105 dm3 mol-1 cm-1. Beer's law is obeyed up to 10.0 mg Co/25 mL. The ratio of Co:TAMB in the complex is 1:3 by different methods; the oxidation state of cobalt ions in the complex is Co3+. The L-M electronic transition of the complex was proved.

Key words: ULTRAVIOLET SPECTROPHOTOMETRY, MICELLE, COBALT, INFRARED SPECTROPHOTOMETRY, COLOUR REAGENTS, COLOR REACTION, BENZENECARBOXYLIC ACID P, NON IONIC SURFACTANTS, COBALT COMPLEX, THIAZOLE-AZO COMPOUNDS