Monolithic column modified with bifunctional ionic liquid and styrene stationary phases for capillary electrochromatography

- Ionic liquid and styrene are made on monolithic column as bi-functional stationary phase.
- Simple single-step copolymerization was used in preparation of CEC column.
- Ionic liquid improves monolith morphology and electroosmotic flow.
- Column exhibits excellent separation selectivity, high column efficiency, good stability and reproducibility.

A novel monolithic column with ionic liquid and styrene-modified bifunctional group was prepared for capillary electrochromatography (CEC) by in situ copolymerization in a ternary porogenic solvent. Ionic liquid (1-allyl-methylimidazolium chloride, AlMeIm+Cl−) and styrene served as the bifunctional monomer, while ethylene dimethacrylate (EDMA) was used as the cross-linker. The monomer of AlMeIm+Cl− was introduced as anion-exchange group, while styrene as hydrophobic and aromatic group; the similar conjugated structure in AlMeIm+Cl− and styrene was beneficial for offeing obvious synergistic effect. The bifunctional stationary phase possessed powerful selectivity for the separation of neutral compounds, acidic analytes and phenols. The highest column efficiency was 2.70 × 105 plates m−1 (theoretical plates, N) for toluene. A relatively strong electroosmotic flow (EOF) was obtained in a wide range of pH values from 2.0 to 12.0, which could successfully achieve the rapid separation of the analytes within 10 min. The proposed monolithic column was characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR). The results indicated that the resultant monolithic column had good permeability and excellent mechanical stability. Good reproducibility was obtained with relative standard deviations (RSDs) of the retention time in the range of 0.24-0.47% and 0.81-2.17% for run-to-run (n = 5) and day-to-day (n = 5), while 1.09-2.70% and 0.98-1.70% for column-to-column (n = 3) and batch-to-batch (n = 3), respectively. The combination of AlMeIm+Cl− and styrene was a promising option in the fabrication of the organic polymer monolithic column.