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

A multiwavelength spectrophotometric (WApH) titration method for determinat ion of acid dissociation constants (pK(a) values) of ionizable compounds de veloped previously was applied in the case of pyridine derivatives of pharm aceutical interest. Specifically, UV absorption spectra of the drug solutio n are acquired in the course of a pi-I-metric titration using an optical de vice based on a fibre optics dip probe, a light source and a diode array de tector. 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 de monstrated that the WApH technique in this case outperforms conventional pH -metric methods with respect to the measurement of pK(a) values of the spar ingly water soluble samples reported in this study. (C) 1999 Elsevier Scien ce B.V. All rights reserved.