Determination of Co(II) in pharmaceutical formulations and evaluation of formed species during complexation by UV-Vis with Br-TDB

Abstract

The goal of this work was to determine cobalt in pharmaceutical formulations and the formed species during complexation with 6-[2'-(5-bromothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic reagent (Br-TDB). The log β values for the formed complex species ML2H24-, ML2H5- and ML26- (M = Co(II) and L = Br-TDB4-) were 29.26 ± 0.03, 25.11 ± 0.04 and 16.7 ± 0.11. The stoichiometry of the complex is 1:2 and the time of reaction equals 10 minutes. The complex absorbs at 620 nm. The limits of quantification and detection were equal to 0.009 and 0.030 mg L-1, respectively. The analytical curve presented an unusual pattern with negative angular coefficient. The pattern is intrinsic to the complexation system with Br-TDB, once the same behavior was observed in determination of manganese, lead, cadmium and iron ions by UV-Vis. The methodology was validated by ICP OES. The concentration of cobalt in analyzed drug samples was coincident with manufacturer's information. Moreover, both UV-Vis and ICP OES yielded similar results at a confidence level p<0.05.