RESUMO
Three highly sensitive organic reagents for the Spectrophotometric deter-1 ruination of cobalt are l-nitroso-2-naphthol, 2-nitroso-l-naphthol and nitroso-R-salt. They are specific for cobalt under some conditions. The first two reagents are used in extractive spectrophotometric methods, while the third enables cobalt to be determined in aqueous media. The thiocyanate method, either with or without an extraction step is suitable for the determination of relatively large amount of cobalt. In recent years there has been a remarkable growth in the number of sensitive methods for cobalt determination based on azo compounds e.g. PAN, PAR and some other pyridine azo compounds. Most of the developed methods applied extractive methods to achieve selectivity. Schaffer acid [2-hydroxynaphthalene-6-sulphomc acid] azo dyes were used as Spectrophotometric reagents for copper and tungsten [VI]. The ionization constants of substituted phenyl-azo-schaffer acid were determined spectrophotometrically in aqueous buffer solutions