Jahan B. Ghasemi* and Noushin Mandoumi
Chemistry Department, Faculty of Sciences, Razi University, Kermanshah, Iran
* Corresponding author: E-mail: Jahan.ghasemi@gmail.com
Abstract
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.