Fabrication and evaluation of a dual-zwitterionic functionalized hydrophilic monolith for chromatographic separation

In this study, the chromatographic performance of a novel dual-zwitterionic hydrophilic stationary phase were investigated. Three zwitterionic HILIC monoliths were prepared using 3-(4-((methacryloyloxy)methyl)-1-methylpiperidin-1-ium-1-yl)propane-1-sulfonate (MAMMPS), 2-methacryloyloxyethyl phosphorylcholine (MPC), and a combination of MAMMPS and MPC (1:1, molar ratio) with N,N'-methylenebisacrylamide (MBA), separately. The monoliths exhibited good repeatability and stability. A high column efficiency of 120,000 plates/m was reached on the novel dual-zwitterionic functionalized poly(MAMMPS@MPC-co-MBA) monolith. Through the analysis and testing with different standards, the poly(MAMMPS@MPC-co-MBA) monolith exhibited the strongest retention capacity for negatively charged benzoic acid derivatives due to its high hydrophilicity and weak electronegativity. In contrast, the poly(MPC-co-MBA) monolith, functionalized with a single zwitterion, facilitated electrostatic interactions with negatively charged analytes. Baseline separation was achieved on all three monoliths for selected nucleobases, nucleosides, phenol derivatives, and amine compounds. However, their retention strength was mainly related to the hydrophilicity of the stationary phases, while hydrogen bonding and electrostatic interactions played secondary roles. Among the monoliths, the poly(MAMMPS-co-MBA) monolith demonstrated the best separation for neutral, acidic, and alkaline compounds. These findings offer valuable insights for the future selection and application of dual-zwitterionic HILIC monoliths for chromatographic separations.