Enantioseparation and Determination for Racemate Carnitine Based on a Chiral Hybrid Material Synthesized by Metal Organic Framework and Covalent Organic Framework in Capillary Electrochromatography.

In this work, a CDs-TpBD/UiO-66 hybrid material was firstly synthesized via Schiff base reaction using isocyanate-β-cyclodextrin (CDs) as a chiral modifier, TpBD COF and UiO-66-NH2 MOF as the frameworks, and was characterized by Fourier-transform infrared spectra, scanning/transmission electron microscopy, X-ray diffraction spectra, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption, and thermogravimetric analysis. The results showed that the hybrid material exhibited a close-packed structure of TpBD and UiO-66-NH2 crystal, well-defined micropores, and good stability. It was used as the stationary phase in open-tubular (OT) capillary electrochromatography, and 7 amino acids (basic: D/L-arginine, D/L-histidine, D/L-lysine; neutral: D/L-methionine, D/L-valine; acidic: D/L-aspartate, D/L-glutamic acid) and D/L-carnitine (D/L-Car) were baseline separated under the optimal chromatographic conditions within 6 min by capillary electrochromatography. The resolution (Rs) ranged from 1.50 to 5.41, and the selectivity factor (α) ranged from 1.08 to 2.52, respectively. Enantioseparation was attributed to the synergistic effect of CDs, TpBD, and UiO-66-NH2 in the stationary phase as well as the difference of adsorption and selectivity between the enantiomers and the stationary phase through the adsorption experiments. The detection method of D/L-Car was established by CDs-TpBD/UiO-66 OT column. Good linearity (R2 ≥ 0.999) was obtained in the concentration ranges of 8.5-200 μg/mL for D-Car and 7.0-200 μg/mL for L-Car with detection limits of 2.5 and 2.1 μg/mL, respectively. The developed method was simple, rapid, high efficiency as well as broad application, and could be applied for the simultaneous separation and detection of D/L-Car in actual samples.