Investigation of copper chelate of beta-cyclodextrin by spectrophotometric titration with EDTA using window factor analysi

Copper(II) is known to form a 2:1 complex with beta-cyclodextrin in alkaline solution (pH ≥ 12), but its formation constant has not been determined. The present investigation involved determination of the formation constant of the complex by spectrophotometric titration with ethylenediaminetetraacetic acid (EDTA) using Window Factor Analysis (WFA). WFA is a self-modeling chemometric technique that extracts the concentration profiles of individual species from evolutionary processes such as complexometric titration. Eleven aqueous solutions at fixed pH (pH ≥ 12) were prepared. Each solution contained a fixed amount of copper and cyclodextrin and different amount of EDTA. The visible absorption spectrum of each sample was recorded from 900 nm to 500 nm. The number of components responsible for the spectral data were determined by Principal Factor Analysis (PFA). The concentration profiles of the complexes formed were determined using WFA. Applying stoichiometric balance to the concentration profiles, the titration complex was determined to be (Cu2HO 2CD.EDTA)-7, and its logarithm of formation constant was calculated to be 8.51 +/- 0.21. The logarithm of dissociation constant for the dissociation of the titration complex into (Cu(OH)(EDTA))-3 was calculated to be -1.99 +/- 0.21. Using this information and considering the solubility product constant of Cu(OH)2 as well as the formation constant of (Cu(OH)(EDTA))-3, the logarithm of formation constant of (Cu2HO2CD)-3 was calculated to be 35.64 +/- 0.38.