Pyridylazo-diaminobenzenes as reagents for cobalt: Spectrophotometric determination of cobalt in silicates and meteorites

Six pyridylazo-diaminobenzenes have been synthesized and assessed as chromogens for the spectrophotometric determination of traces of cobalt. Five of the reagents having chloro-, bromo- and iodo-substitutions on the heterocyclic ring show high colour stabilities and extreme sensitivities in their reactions in strongly acidic medium. The effective molar absorptivities range between 1.00 and 1.23·10⁵ 1 mole^-1 cm^-1. Only iron and chromium(VI) interfere; the presence of fluoride and hydroxylamine makes the reactions specific. 4-(5-Bromo-2-pyridylazo)-1,3-diamino-benzene has been applied to the determination of cobalt in silicate rocks and meteorites with good precision and accuracy.