MODELING RETENTION OF IONOGENIC SOLUTES IN LIQUID-CHROMATOGRAPHY AS AFUNCTION OF PH FOR OPTIMIZATION PURPOSES

In liquid chromatography, the retention of ionogenic solutes is a stro ng function of the pH of the mobile phase, with different solutes show ing different behaviour, both qualitatively (e.g., acids vs. bases) an d quantitatively (values of dissociation constants). Thus, pH will als o affect selectivity and it can be used as a parameter for optimizing separations. In many instances, such optimization studies will require an accurate description of retention as a function of pH. In this pap er, attention is focused on basic models describing retention as a fun ction of pH and their use in practice. The theoretical, sigmoidal curv e is discussed and a number of possible causes of deviations are consi dered. The inaccuracies introduced by linearly or quadratically interp olating part of a sigmoidal curve are addressed, in addition to the se nsitivity of sigmoidal interpolation to experimental errors.