Spectroscopic study of Alizarin Red S binding with cetyltrimethylammonium bromide at low concentrations

The anthraquinoid dye, Alizarin Red S, forms an anionic moiety in aqueous solution. The complex formation of this dye was studied with the cationic surfactant, cetyltrimethylammonium bromide, in an aqueous environment at low surfactant concentrations. The complex was studied with the help of ultraviolet-visible spectroscopy. A method of continuous variation was applied to confirm the complex formation and showed that a 1:1 complex was evident from the experimental results. The equilibrium constant for the formation of the complex was determined at various temperatures. Different thermodynamic parameters, free energy of binding, enthalpy of binding and entropy of binding were calculated.