Novel cationic polyelectrolyte coatings for capillary electrophoresis

Area of Science:

• Analytical Chemistry
• Separation Science
• Materials Science

Background:

• Bare fused silica capillaries in capillary electrophoresis (CE) suffer from sample adsorption and electroosmotic flow (EOF) instability.
• Surface modification of capillaries is crucial for improving separation performance and reproducibility in CE.
• Polyelectrolyte coatings (PECs) offer a promising approach to mitigate issues associated with bare capillaries.

Purpose of the Study:

• To present and characterize two novel polyelectrolyte coatings (PECs): poly(2-(methacryloyloxy)ethyl trimethylammonium iodide) (PMOTAI) and poly(3-methyl-1-(4-vinylbenzyl)-imidazolium chloride) (PIL-1).
• To evaluate the stability, EOF characteristics, and separation capabilities of these PECs in CE under various buffer conditions.
• To assess the hydrophobicity of the PECs for separating lipophilic compounds and specific drug classes.

Main Methods:

• Fabrication and characterization of PMOTAI and PIL-1 coated fused silica capillaries.
• Stability testing of PECs across a range of pH, ionic strength, and buffer compositions.
• Quartz crystal microbalance (QCM) for PEC layer thickness determination.
• Hydrophobicity assessment using alkyl benzoates and distribution constants (log Po/w).
• Separation of model compounds including $\beta$-blockers and ionic liquid hydrolysis products.

Main Results:

• Both PMOTAI and PIL-1 coatings demonstrated semi-permanent stability for at least five runs, requiring minimal regeneration.
• PECs exhibited reduced stability at pH 11.0, with higher EOF observed using Good's buffers compared to sodium phosphate buffer.
• PEC layer thicknesses were measured at 0.83 nm (PMOTAI) and 0.52 nm (PIL-1).
• Comparable hydrophobicity for both PECs enabled the separation of compounds with log Po/w > 2.
• Successful separation of cationic drugs ($\beta$-blockers) and ionic liquid hydrolysis products under conditions where bare capillaries failed.

Conclusions:

• PMOTAI and PIL-1 are effective polyelectrolyte coatings for capillary electrophoresis, enhancing capillary performance.
• These PECs provide stable, hydrophobic surfaces suitable for separating challenging analytes, including pharmaceuticals and ionic compounds.
• The developed coatings offer a viable alternative to bare fused silica capillaries for specific analytical applications.