Modeling of ion-pairing effect in peptide reversed-phase chromatography.

The modeling of counterion and organic modifier concentration effects in peptide APIs reversed-phase preparative chromatography is discussed in this manuscript. A stoichiometric retention model based on the counterion binding to the charged functional groups of the peptide is proposed. The model parameters were evaluated using a rather large set of retention data measured in mobile phases with various counterions and acetonitrile concentrations. The model parameters were experimentally validated by a new counterion binding measurement technique. The n(max) model parameter value was found to be equal to the peptide net charge, whereas the K model parameter value was found to be specific to the counterion type (i.e. AcO(-)