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Complexation of 6,7-dihydroxy-2,4-diphenylbenzopiriliym with Bi(III) and its spectrophotometric determination in pharmaceuticals
Authors: A.N. Chebotarev, D.V. Snigur, D.A. Barbalat, K.V. Pluta, A.S. Koicheva
Number of views: 336
The complexation of Bi(III) with 6,7-dihydroxy-2,4-diphenylbenzopiriliym (R) has been studied. It is found that two complexes of different stoichiometry are formed in the system under study. The complex with the composition Bi(III):R = 1:2 (λ = 510 nm, ε = 28000) is formed at pH 1.9, whereas the complex Bi(III):R = 1:1 (λ = 550 nm, ε = 31000) is formed at pH 4.6. The mechanism of the complexation of Bi(III) with 6,7-dihydroxy-2,4-diphenylbenzidine chloride in solution has been determined based on the spectrophotometric results. In highly acidic medium (pH 1.9), the coordinating ion is BiOH2+ and coordinated ligand is ortho-diphenol form of the reagent. At lower acidity (pH 4.6), the complexing agent is Bi(OH)2+ ion and the reagent reacts in the form of anhydrobase. The complex with the molar ratio of 1:2 is recommended as an analytical form. Beer law is observed in the Bi(III) concentrations range of 0.30 to 6.30 μg/mL. The detection limit is 0.03 μg/mL and the limit of quantification is 0.32 μg/mL. The influence of extraneous ions on the absorbance of the proposed analytical form has been studied. A simple method of spectrophotometric determination of Bi(III) with 6,7-dihydroxy-2,4-diphenylbenzopiriliym in pharmaceuticals has been developed.