Complexation in the retention of benzoic acids on a bonded xanthine HPLC stationary phase

Design and synthesis of a theophylline bonded-phase column for HPLC — application to separation of aromatic carboxylic acids

A stationary phase has been designed and synthesized in which theophylline residues are covalently bonded to a silica support through an eight carbon hydrocarbon linkage. The phase offers improved resolution in the separation of aromatic carboxylic acids over that available with conventional reversed phase supports. The column is relatively stable. Retention can be modified by adjusting mobile phase composition with respect to pH, electrolyte type and concentration, and organic modifier as well as by manipulating the temperature at which chromatography is carried out. The capacity factors, k', for a series of ring substituted benzoic acids were correlated with the complexation constants previously reported for these compounds with theophylline in bulk phase solution.