Relationship between micellar liquid chromatography retention of sulfonamides and the pH and concentration of surfactants and organic modifiers in the mobile phase

The paper presents an attempt to adapt a retention model suggested and verified by classic RP LC in micellar liquid chromatography, MLC. Instead of hydrophobic interactions with ODS groups and electrostatic interactions with silanol residues in C-18 packing, hydrophobic interactions with alkyl groups and ionic interactions with anionic moieties of the SDS-modified stationary phase were considered. Due to the different characteristics of the stationary phase in the MLC depending on the pH of the mobile phase, the equation used to determine the contribution of electrostatic interactions to retention was modified. Theoretical curves for the relationship between retention and SDS micelle concentration in the mobile phase, organic modifier concentration and eluent pH were determined. For comparison, curves based on data obtained in basic sulfonamide studies were plotted in the same coordinate systems and units. A complete qualitative similarity was noted between the theoretical curves predicting retention changes with changing micellar mobile phase parameters and the curves determined based on experimental results for the sulfonamides. The qualitative similarity involves a similar shape of the respective curves and identical tendencies. In general, a larger reduction of sulfonamide retention with respect to the predicted value is noted. The deviation results from changes in the sulfonamide property with changing pH of the mobile phase.