Spectrophotometric study of the formation of ternary complexes of iron(III) with some triphenylmethane dyes and cationic surfactants

Abstract

The optimum conditions have been found for the formation of the ternary complexes of iron(III) with Chrome Azurol S (CAS), Eriochrome Cyanine R, and Pyrocatechol Violet in the presence of cetyltrimethylammonium (CTA), cetylpyridinium, or tetradecyldimethyl-benzylammonium ions. The pH range of the complex formation is limited mainly by the pertinent hydrolysis constants of the metal ions. The maximum absorbances were obtained for excess R and cationic surfactants, ensuring the formation of complexes with the highest R:Fe molar ratio. The method based on the Fe-CAS-CTA system (ϵ = 1.32 × 10 5 liter mol −1 cm −1 at 628 nm) is most sensitive and is recommended for the spectrophotometric determination of iron.