Multiwavelength spectrophotometric determination of acid dissociation constants: Part IV. Water-insoluble pyridine derivatives

Abstract

A multiwavelength spectrophotometric (WApH) titration method for determination of acid dissociation constants (p K a values) of ionizable compounds developed previously was applied in the case of pyridine derivatives of pharmaceutical interest. Specifically, UV absorption spectra of the drug solution are acquired in the course of a pH-metric titration using an optical device based on a fibre optics dip probe, a light source and a diode array detector. Target factor analysis was applied to deduce the p K a values from the spectral data recorded at different pH. Using this technique, the p K a values of six pyridine derivatives were determined successfully. It was demonstrated that the WApH technique in this case outperforms conventional pH-metric methods with respect to the measurement of p K a values of the sparingly water soluble samples reported in this study.