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, vinylbenzyl trimethylammonium chloride and the cross-linker of ethylene dimethacrylate by in-situ copolymerization in binary porogenic solvent consisting of cyclohexanol and dodecanol for capillary electrochromatography. The stationary phases formed by styrene-based monomers can provide 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 basing on the combination of binary RPLC and HILIC separation mechanism. Vanillin substances, neutral and alkaline compounds can be separated perfectly on the monolithic column under different chromatographic modes which can be switched by changing the content of organic modifier in running phase. For benzene, the highest column efficiency was 3.49 × 105 plates m-1 (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.