title: Multiwavelength spectrophotometric determination of acid dissociation constants: Part III. Resolution of multi-protic ionization systems.
abstract: A multiwavelength spectrophotometric (WApH) titration method was applied to study several multi-protic histamine H2-receptor antagonists which involved four acid dissociation constants (pKa values) over the pH range of 2-10. Specifically, UV absorption spectra of the drug solution were 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 utilized to deduce the pKa values from the spectral data recorded at different pH. It was noted that some of the pKa values were within mid pH range which were difficult to obtain because of insufficient absorption spectra acquired in the un-buffered region of the titration curve. With the aid of the WApH technique coupled with an optically transparent buffer, all pKa values have been successfully determined and were in excellent agreement with those measured using a conventional pH-metric method.
authors.affiliation: SmithKline Beecham Pharmaceuticals, New Frontiers Science Park (North), Harlow, Essex, UK.
authors.forename: R C
authors.initials: RC
authors.lastname: Mitchell
authors.forename: C J
authors.initials: CJ
authors.lastname: Salter
authors.forename: K Y
authors.initials: KY
authors.lastname: Tam
mesh_terms: D000465:Algorithms; D006634:Histamine H1 Antagonists / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D011725:Pyridines / Q000032:analysis*; D011744:Pyrimidinones / Q000032:analysis*; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet
chemical_list: D006634:Histamine H1 Antagonists; D011725:Pyridines; D011744:Pyrimidinones; C043465:icotidine; C049054:temelastine; C101022:lupitidine