Vacuum-assisted thermal bonding of ?-cyclodextrin and its derivatives as chiral stationary phases for high-performance liquid chromatography

In this work, the vacuum-assisted thermal bonding method was proposed for the covalent coupling of beta-cyclodextrin (beta-CD) (CD-CSP), hexamethylene diisocyanate cross-linked beta-CD (HDI-CSP) and 3, 5-dimethylphenyl isocyanate modified beta-CD (DMPI-CSP) onto the isocyanate silane modified silica gel. Un-der vacuum conditions, the side reaction due to the water residue from the organic solvent, air, reaction vessels and silica gel could be avoided, and the optimal temperature and time of vacuum-assisted ther-mal bonding method were determined as 160 degrees C and 3 h. These three CSPs were characterized by FT-IR, TGA, elemental analysis and the nitrogen adsorption-desorption isotherms. The surface coverage of CD-CSP and HDI-CSP on silica gel was determined as similar to 0.2 mu mol m-2, respectively. The chromatographic performances of these three CSPs were systematically evaluated by separating 7 flavanones, 9 triazoles and 6 chiral alcohols enantiomers under the reversed-phase condition. It was found that the chiral reso-lution ability of CD-CSP, HDI-CSP and DMPI-CSP was complementary to each other. Among them, CD-CSP could separate all 7 flavanones enantiomers with the resolution of 1.09-2.48. HDI-CSP had a good separa-tion performance for triazoles enantiomers with one chiral center. DMPI-CSP showed excellent separation performance for chiral alcohol enantiomers, among which the resolution of trans-1, 3-diphenyl-2-propen-1-ol reached 12.01. Generally, the vacuum-assisted thermal bonding had been demonstrated as a direct and efficient method for the preparation of chiral stationary phases of beta-CD and its derivatives.(c) 2023 Elsevier B.V. All rights reserved.