Spectral analysis of complexes of the dye, 3,3 '-diethyl thiacyanine and the anionic surfactant, SDS by the principal component analysis method

The spectroscopic feature of the interaction of a cationic dye, 3,3'-diethy l thiacyanine iodide (THIA), with an anionic surfactant, sodium dodecyl sul phate (SDS), in aqueous medium is discussed. SDS induces two metachromatic peaks in THIA at 404 and 380 nm at premicellar concentrations and only the monomeric peak at 425 nm at high postmicellar concentrations. The principal component analysis (PCA) method has been applied to determine the composit ions as well as molar absorption coefficient (epsilon) spectra of the metac hromatic dye-surfactant complexes. Results of the PCA method definitely sho w that the observed peaks at 425, 404 and 380 nm of THIA in the presence of SDS at appropriate concentrations are due to the monomer, dimer, and trime r of THIA, respectively. Moreover, the equilibrium constant between monomer and trimer of the dye and surfactant has also been calculated by the metho d followed by Vitagliano et al., and found to be in close agreement with th at obtained by the PCA method. (C) 1999 Elsevier Science B.V. All rights re served.