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

摘要

A multiwavelength spectrophotometric (WApH) titration method for determination of acid dissociation constants (pK_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 pK_a values from the spectral data recorded at different pH. Using this technique, the pK_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 pK_a values of the sparingly water soluble samples reported in this study.