Mixed-Mode Acrylamide-Based Continuous Beds Bearing tert-Butyl Groups for Capillary Electrochromatography Synthesized Via Complexation of N-tert-Butylacrylamide with a Water-Soluble Cyclodextrin. Part II: Effect of Capillary Size and Polymerization Conditions on Morphology and Chromatographic Efficiency

In this series, we investigate the impact of the complex formation constant of the hydrophobic monomer with respect to statistically methylated-?-cyclodextrin (Me-?-CD) on the electrochromatographic properties of highly crosslinked amphiphilic mixed-mode acrylamide based monolithic stationary phases. In the first part, we investigated the retention properties. In the present study, we optimize the synthesis parameters with respect to obtainable morphology and separation efficiency. For this purpose, a series of mixed-mode acrylamide-based continuous beds bearing tert-butyl groups is synthesized under systematic variation of (i) the concentration of the lyotropic salt ammonium sulfate in the polymerization mixture and (ii) the dimension of the capillary. The impact of these parameters on the chromatographic efficiency is studied under isocratic conditions for alkylphenones in the reversed-phase mode via capillary electrochromatography with varied electric field strength. As expected, there is a strong impact of the concentration of ammonium sulfate in the polymerization mixture on the morphology (examined via scanning electron microscopy) and on the chromatographic efficiency, while there is only a minor influence when varying the size or the shape of the capillary cross-sectional area. Morphology and chromatographic efficiency of this new type of stationary phase are compared to those reported in our previous series. The studies reveal a significant influence of the formation constant of the formed inclusion complex on the morphology and the chromatographic efficiency for those monoliths having a large domain size, while there is an insignificant influence for those monoliths having a small domain size.