Spectrophotometric determination of acidity constants of 2-(2-Thiazolylazo)-Cresol in various water-organic solvent media mixtures using chemometrics methods. 
The combination of soft- and hard-modeling was used to the spectrophotometric studies of the acidity constants of 2-(2-Thiazolylazo)-Cresol (TAC) at 25°C and at ionic strength 0.1 mol L(-1) in pure water as well as in aqueous media containing variable percentages (10-50%) of organic solvents.  The organic solvents used were methanol, ethanol, dimethyl formamide (DMF) and 1,4-dioxane.  The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model.  DATAN program was applied for determining acidity constants and pure spectra of different form of TAC.  Results show that the acidity constants of TAC are influenced as the percentages of solvents added to the solution.  The corresponding pKa values in solvent-water mixtures were determined.  There are linear relationships between acidity constants and the mole fraction of organic solvents in the solvent mixtures.  The effects of various solvents on absorption properties and acidity constants of each component are also discussed.