A reversed-phase/hydrophilic bifunctional interaction mixed-mode monolithic column with biphenyl and quaternary ammonium stationary phases for capillary electrochromatography

A novel organic polymer monolithic column with reversed-phase/hydrophilic (RPLC/HILIC) bifunctional interaction mixed-mode was successfully synthesized with the monomers 4-vinylbiphenyl and vinylbenzyl trimethylammonium chloride and the cross-linker ethylene dimethacrylate by in situ copolymerization in a binary porogenic solvent consisting of cyclohexanol and dodecanol for capillary electrochromatography. The stationary phases formed by styrene-based monomers can allow powerful π–π, hydrophobic and hydrophilic interactions, which is beneficial for the chromatographic separation with high resolution and high column efficiency. One mixed-mode monolithic column can work as two individual mode columns based on the combination of binary RPLC and HILIC separation mechanisms. Vanillin substances and neutral and alkaline compounds can be separated perfectly on the monolithic column in different chromatographic modes which can be switched by changing the content of the organic modifier in the running phase. For benzene, the highest column efficiency was 3.49 × 105 plates per m (theoretical plates, N). The relative standard deviations of retention time of different test analytes for intra-day (n = 5), inter-day (n = 5), column-to-column (n = 3) and batch-to-batch (n = 3) reproducibility were all less than 5.0%. All these results demonstrate that the monolithic column with RPLC/HILIC mixed-mode has great application potential.