β-Cyclodextrin-modified covalent organic framework as chiral stationary phase for the separation of amino acids and β-blockers by capillary electrochromatography.

Covalent organic frameworks (COFs) as a novel stationary phase have attracted much attention in the field of chromatography owing to their permanent nanoscale porosity, higher surface area, and exceptional stabilities. Here, a novel isocyanate-β-cyclodextrin-modified COF (MDI-β-CD-modified COF) was synthesized using isocyanate-β-cyclodextrin as the chiral selector and imine-based TpPa-1 COF as the matrix by a bottom-up strategy. The reaction condition and the structure of MDI-β-CD-modified COF were optimized and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra, nitrogen adsorption/desorption (Brunauer-Emmett-Teller [BET]), and thermogravimetric analysis (TGA). And then the coated open-tubular column (OT column) was prepared using MDI-β-CD-modified COF as chiral stationary phase (CSP) by in situ growth approach, which exhibited excellent stability and repeatability. For seven consecutive runs, the intraday and interday relative standard deviations (RSDs) were in range from 0.35% to 2.21% for the migration time of histidine. The column-to-column reproducibility ranged from 2.39% to 3.08%. Meanwhile, the separation of eight compounds including four amino acids and four β-blockers by capillary electrochromatography sufficiently verified the favorable chiral resolution properties of the MDI-β-CD-modified COF-coated OT column. This strategy of fabricating MDI-β-CD-modified COF-coated OT column expanded the application of imine-based COFs in chromatographic analytical fields.