Zwitterionic imidazolium sulfonate functionalized polymeric monolith for mixed-mode HILIC/RPLC applications

To meet the increasing demand for the separation of complex samples, a novel monolithic stationary phase with hydrophobic and hydrophilic functionalities was developed by using 3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium) propane-1-sulfonate (VBIPS) as monomer, pentaerythritol triacrylate (PETA) as crosslinker. The optimized mixed-mode poly(VBIPS-co-PETA) monolith exhibited good mechanical strength, high permeability (K = 0.23 × 10^-14 m² in 100 % ACN, 0.23 × 10^-14 m² in 100 % MeOH, and 0.11 × 10^-14 m² in 100 % H₂O), and multiple interaction modes, including hydrophilic, hydrophobic, hydrogen, and electrostatic interactions. The highest column efficiency of 83,330 plates/m was achieved for thiourea at a linear velocity of 0.23 mm/s. Systematic evaluations confirmed strong retention and separation of polar substances (e.g., benzoic acids, nucleoside bases, phenols), primarily due to the sulfobetaine-derived hydrophilicity as well as effective separation of nonpolar substances (e.g., aniline, aryl ketones, polyaromatic hydroxy compounds), facilitated by π-π stacking interactions between analytes and benzene rings within the stationary phase. Overall, this zwitterionic imidazolium sulfonate-functionalized monolith successfully combines hydrophobic and hydrophilic groups in a single continuous bed, enabling efficient separation of both polar and nonpolar analytes under low backpressure. This work enriches the library of mixed-mode stationary phases, and broadens the detection scope for complex sample analysis.