Secondary chemical equilibria in high-performance liquid chromatography: influence of ionic strength and pH on retention of peptides

In this work a model describing the effect of pH on retention in LC is established and tested for two series of peptides using an octadecylsilica column. The suggested model uses the pH value measured in the acetonitrile-water mixture instead of the pH value in water and takes into account the effect of the activity coefficients. The proposed equations permit the prediction of the pH optimum using a minimum number of measurements and can be combined with the previously derived equations, that relate the retention with the solvent composition of the mobile phase, to establish a general model that relates the elution behaviour of the solute with the significant mobile phase properties: composition, pH and ionic strength. (C) 1998 Elsevier Science B.V. All rights reserved.