Zwitterionic polymeric monoliths for HILIC/RP mixed mode for CEC separation applications

Area of Science:

• Analytical Chemistry
• Separation Science
• Materials Science

Background:

• Development of versatile stationary phases for capillary electrochromatography (CEC) is crucial for advanced separations.
• Existing CEC stationary phases often lack the ability to perform multiple separation modes, limiting their applicability.
• Zwitterionic materials offer unique surface properties beneficial for chromatographic applications.

Purpose of the Study:

• To synthesize polymer-based monoliths with zwitterionic surface character for use as versatile electrochromatographic stationary phases.
• To investigate the potential of these monoliths for both hydrophilic interaction (HILIC) and reversed-phase (RP) separation modes.
• To explore methods for tuning the electroosmotic flow (EOF) and separation selectivity.

Main Methods:

• UV-initiated free radical copolymerization of N-acryloxysuccinimide and ethylene dimethacrylate in capillary columns.
• Two-step synthesis involving initial monomer polymerization followed by surface modification via nucleophilic substitution and hydrolysis.
• Grafting of hexyldiamine to introduce cationic surface charges and subsequent characterization of monolith properties.

Main Results:

• Successfully synthesized polymer-based monoliths with tunable zwitterionic surface character.
• Demonstrated the ability to achieve both HILIC and RP separation modes using the same stationary phase.
• Showed that mobile phase pH can effectively tune the intensity and direction of the EOF.
• Confirmed that mobile phase composition governs the interfacial interaction processes and separation behavior.
• Proposed polymer backbone hydrophilization and shorter alkyldiamine grafting as strategies to enhance HILIC performance.

Conclusions:

• The developed zwitterionic monoliths represent versatile stationary phases for CEC, capable of multiple separation modes.
• The synthesis strategy allows for control over surface charge and EOF, enabling tailored chromatographic performance.
• Further optimization, including hydrophilization and modified grafting, can enhance specific separation capabilities like HILIC.