Preferential solvation and perichromic behavior of the dyes indigo carmine, amaranth and tartrazine: Spectroscopic approach using binary mixtures

Abstract The spectroscopic characteristics of three food dyes, two azo dyes (amaranth and tartrazine) and one indigo dye (indigo carmine), were studied using five amphiprotic alcohols in solvent mixtures: water-methanol, water-ethanol, water-iso-propanol, water-n-propanol and water-t-butanol. The preferential solvation of each dye in different binary mixtures was investigated. The dyes studied are widely used as food dyes and although they do not have solvatochromic properties slight spectroscopic changes were observed in the binary mixtures in the presence of tartrazine and indigo carmine. Tartrazine (TTY) presented spectral changes at the maximum wavelength (λmax) in the ultraviolet region while indigo carmine (INC) presented spectral changes at λmax in the visible region of the electronic spectrum. The parameters obtained from the nonlinear fit of the preferential solvation (PS) indicate that with the use of TTY as a spectroscopic probe the parameters f12/1 and f2/1 being >1 for the mixtures water-iso-propanol and water-t-butanol for which the values are less than 1 (