Application of a Second-Order Derivtive Spectroscopic Technique: Determination of the Ionization Constants of Phenytoin and Phenobarbital

Abstract

Absorption spectroscopy can be used to determine the pK of a compound when a change in the spectral pattern can be related to a change in the protonation state of an ionizable group. The calculation of a pK becomes difficult (standard error increases) when these spectral changes are indistinct or are minimally resolved. In these cases, the ability of higher-order derivative spectroscopy to enhance the short-range fine structure of a spectra usually offers adequate spectral resolution for quantitative pK determinations.