A New Algorithm for the Characterization of Thermodynamics of Monomer-Dimer Process of Dye Stuffs by Photometric Temperature Titration

Jahan B. Ghasemi* and Noushin Mandoumi

Chemistry Department, Faculty of Sciences, Razi University, Kermanshah, Iran
* Corresponding author: E-mail: Jahan.ghasemi@gmail.com

A method of data analysis for monomer-dimer equilibria employing multiwavelength detection is shown to recover both the thermodynamic constants and absorption spectra of monomer-dimer pairs in complex mixtures. Using UV-Vis spectroscopy the dimerization constants of crystal violet (CV), resazurine (R) and methylene blue (MB), that they are severely overlapped, have been determined by studying the dependence of absorption spectra on temperature in range 0–90 °C and an iterative least-squares method. The proposed method has previously proposed by Frans, S. D.; Harris, J. M.; Anal. Chem. 1984, 56, 466–470 for the resolving of mixtures of four acid molecules by pH titration. In contrast to the Kubista’s method Anal. Chem. 1993, 65, 994–998 which relay on the prior knowledge of the monomer spectrum our method is free of advance any known values. The resolving power of the method is tested by studying of the mixtures of dye molecules. The multiple wavelength titration curves are used to form matrix, D, which is then factored into matrices A, containing the absorption spectra of the components, and C, containing their temperature-dependent concentrations. The correct KD(T)'s and absorption spectra are derived by a least-squares minimization with KD(T)'s as adjustable parameter.

Keywords: Dimerization; iterative least-squares; UV-Vis spectroscopy; crystal violet; resazurine; methylene blue.