Spectrophotometric and thermodynamic studies on the protonation and copper complexation equilibrium of hydroxynaphthol blue in aqueous solution

The accurate determination of acidity and stability constants values are fundamental to understanding the behavior of ligands and their interaction with metal ions in aqueous solution. Such an understanding is important in a wide variety of areas, such as metal ions in biology, in biomedical applications, metal ions in the environment, extraction metallurgy, food chemistry and metal ions in many industrial processes. One specific application is the use ofchelating agents in heavy metal ion intoxication treatment. The protonation and Cu(II) complexation of hydroxynaphthol blue (HNB) in ionic strength 0.1 M KNO3 at different temperature has been studied by EQUISPEC program [1-3]. In spectrophotometric titrations, linear or near-linear dependence of concentration profiles and the existence of minor species can cause difficulties in the evaluation of the data. Both calculated absorption spectra and thecorresponding equilibrium constants are not or only poorly defined.The result is the inability to reliably fit a reasonable model to the data. In second order global analysis, a number of spectrophotometric titrations with different initial concentrations are simultaneously analyzed. In this way, conditions for the significant formation of all species can be obtained and consequently theconcentration matrix is augmented to full rank. EQUISPEC is a computer program using the matrix based MATLAB environment for second order global analysis of spectrophotometric equilibrium data. The spectrophotometric titrations were carried out at least in four different metal to ligand ratios.