Ionic liquid-copolymerized monolith incorporated with zeolitic imidazolate framework-8 as stationary phases for enhancing reversed phase selectivity in capillary electrochromatography

A novel ionic liquid (1-allyl-methylimidazolium chloride, AlMeIm+Cl-) polymer monolith poly(ionic liquid-co-ethylene dimethacrylate) incorporated with zeolitic imidazolate framework-8 (ZIF-8-poly(IL-co-EDMA)) was firstly synthesized as stationary phases of monolithic column for capillary electrochromatography by one-step copolymerization. Incorporation of ZIF-8 into ionic liquid polymer monolith evidently enhanced the separation selectivity for four alkylbenzenes in reversed phase capillary electrochromatography (CEC), due to the synergistic effect derived from the same imidazole ring structure of ionic liquid and organic ligands of ZIF-8. Meanwhile, electroosmotic flow (EOF) was generated by ionic liquid in a wide range of pH values from 2.0 to 12.0. The resultant monolithic columns were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR). The results indicated that the prepared monolithic columns had good permeability and mechanism stability. The resultant monolithic columns were applied for the separation of neutral compounds, anilines and phenols. The highest column efficiency was 2.07 × 105 plates m-1 (theoretical plates, N) for toluene. Under optimal conditions, reproducibility was obtained with relative standard deviations (RSDs) of the retention time for run-to-run, day-to-day, column-to-column and batch-to-batch were in the range of 1.58 - 3.19%, 1.92 - 3.87%, 3.84 - 4.96% and 2.63 - 4.33%, respectively. Incorporation ZIF-8 into ionic liquid polymer monolith was a promising way for the application of new materials in the fabrication of novel monolithic columns.