Retention behaviour of peptides, quinolones, diuretics and peptide hormones in liquid chromatography: Influence of ionic strength and pH on chromatographic retention

Peptides, quinolones, diuretics and peptide hormones are important substances of biomedical interest. In this work a model describing the effect of pH on retention in liquid chromatography (LC) is established and tested for these compounds using an octadecylsilica column. The suggested model uses the pH value measured in the hydro–organic mixture used as mobile phase 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 also permit the determination of the acidity constants of the compounds considered in the medium used as mobile phase. Moreover, these equations 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.