High efficiency polyethylene glycol diacrylate monoliths for reversed-phase capillary liquid chromatography of small molecules

• Efficient monoliths were synthesized in capillary columns from polyethylene glycol diacrylates.
• A new statistical model was found to aid porogen selection and morphology optimization.
• Correlation was established between chromatographic efficiency and physical/chemical properties of reagents.
• A corrected chromatographic efficiency of 186,000 plates/m was obtained for a non-retained compound.
• The retention mechanism was primarily reversed-phase with additional hydrogen bonding interaction.

Highly cross-linked monolithic networks (i.e., polyethylene glycol diacrylate, PEGDA) synthesized from monomers containing varying ethylene oxide chain lengths were fabricated inside fused silica capillary columns for use in liquid chromatography (LC) of small molecules. Tergitol was used as a surfactant porogen in combination with other typical organic liquid porogens. Column performance was correlated with quantitative descriptors of the physical/chemical properties of the monomers and porogens using a statistical model. Solubility and viscosity values of the components were identified as important predictors of monolith morphology and efficiency. The chromatographic retention mechanism was determined to be principally reversed-phase (RP) with additional hydrogen bonding between the polar groups of the analytes and the ethylene oxide groups embedded in the monolith structure. The fabricated monolithic columns were evaluated under RPLC conditions using phenols, hydroxy benzoic acids, and alkyl parabens as test compounds. Isocratic elution of hydroxy benzoic acids at a linear velocity of 0.04 cm/s using a PEGDA-700 monolith gave chromatographic peaks with little tailing (i.e., tailing factor < 1.28). The chromatographic efficiency measured for a non-retained compound (uracil) using this column was 186,000 plates/m when corrected for injector dead volume. High resolution gradient separations of selected pharmaceutical compounds and phenylurea herbicides were achieved in less than 18 min. Optimized monoliths synthesized from all four crosslinking monomers exhibited high permeability and demonstrated little swelling or shrinking in different polarity solvents. Column preparation was highly reproducible, with relative standard deviation (RSD) values less than 2.1%, based on retention times of the phenol standards (3 different columns).