Dependence of reversed-phase retention of ionizable analytes on pH, concentration of organic solvent and silanol activity

In reversed-phase chromatography, the retention of ionizable analytes is in fluenced by the ionic properties of the packing caused by surface silanol g roups. We have measured the ion-exchange properties of both reversed-phase bonded phases and their underlying base materials. The probe used in this p art of the study was bretylium tosylate. The acquired knowledge is then use d for a complete and quantitative understanding of the retention behavior o f ionizable compounds as a function of the pH of the mobile phase and the s olvent composition. We have studied the retention pattern of a broad range of acids, bases, and polyfunctional analytes over the pH range from 2 to 11 and from water to 80% acetonitrile. A few application examples demonstrate the relevant findings. (C) 2001 Elsevier Science B.V. All rights reserved.