ABSTRACT. The traditional spectrophotometric determination of stability constants of complexation involves finding a wavelength at which only one of the components has absorbance without any spectroscopic interference of the other reaction components. But this method fails when there is not selective wavelength for at least one of the component. Multivariate data analysis involving soft and/or hard model analysis can be used in these cases. In the present work, firstly, multivariate curve resolustion-alternative least squares which is a model free analysis, was used to estimate the chemical model of data variation and then a robust multi-wavelength model-based method has been developed to determine the stability constants of formed complex(s) regardless to the spectra overlapping of the components. By applying such model, not only the stability constants of the formed complex(s) can be calculated, but also the pure spectra of all contributed components are extracted well. The complexations of 1,10-phenanthroline-5,6-dione ligand with several metalic cations [Cu(II), Ni(II), Co(II), Zn(II)] were studied using proposed multi-wavelength spectrophotometric method in non-aqueous solution at 25 °C. It was found that there is a 2:1 stoichiometry between ligand with studied metalic cations and also their stability constants were calculated.

In traditional spectrophotometric determination of stability constants of complexation, it is necessary to find a wavelength at which only one of the components has absorbance without any spectroscopic interference of the other reaction components. In the present work, a simple multi-wavelength model-based method has been developed to determine stability constants for complexation reaction regardless of the spectra overlapping of components. Also, pure spectra and concentration profiles of all components are extracted using multi-wavelength model based method. In the present work spectrophotometric titration of several cationic metal ions with new synthetic ligand were studied in order to calculate the formation constant(s). In order to estimate the formation constants a chemometrics method, model based analysis was applied.