IR-Spectroscopic Measurement of the p-Nitrophenol - β-Cyclodextrin Equilibrium in Aqueous Solution

Abstract

Two multiwavelength evaluation methods are applied to a matrix of 1R spectra obtained by spectral titration of p-nitrophenol with β-cyclodextrin in an aqueous solution. The first method applied is principal component analysis, which indicates the number of underlying spectra in the matrix to be two. The spectra of p-nitrophenol and its inclusion compound in an aqueous solution can be resolved out of the factors without further assumption as to the titration curve function. The second method used to reconstruct the two spectra is a reiterative nonlinear regression of the entire spectral matrix, using an appropriate model function. By this method the dissociation constant of the complex formation is calculated, but is subject to high uncertainty due to the low signal/noise ratio in IR absorbance spectroscopy. Three of the major objects of spectral titration: determination of the number of factors, resolution of the underlying spectra and fitting to a titration curve function, are accomplished by the evaluation methods.