| Capillary electrochromatography(CEC)monolithic columns have been widely used in the field of enantioseparation in recent years due to their fast mass transfer,high permeability,and uniform aperture.This paper focused on the chiral separation of cyclodextrin(CD)capillary electrochromatographic monolithic columns,expounded the research progress of chiral compounds and enantioseparation,the chiral selective agents for CDs in recent years and in high-performance capillary electrophoresis.The application and the preparation of capillary electrochromatographic monolithic columns were investigated in relevant literature.In this paper,bis[-6-N-(imidazolyl-2-amino-propionic acid-3-)]-?-CD(?-CD-E2)synthesized by a three-step method was used as a chiral selection agent to prepare novel CEC monolithic column by the"one-pot"strategy.Ultraviolet-visible spectrum(UV),Fourier infrared spectrum(FT-IR),X-ray photoelectron spectroscopy(XPS),elemental analysis,nuclear magnetic resonance spectroscopy(NMR),and liquid-mass spectrometry(LC-MS)were used to characterize the product.The results confirmed that the C-6 hydroxyl group on the A and D glucans of?-CD were replaced by histidine group,which made it have amphoteric ionization characteristics and improved the chiral selectivity,stereoselectivity and guest inclusion of?-CD,the results determined it as the target derivative.Then,using?-CD-E2 as chiral monomer,the secondary functional monomer,cross-linking agent,initiator and porogen were added,and the?-CD-E2 monolithic column was prepared by"one-pot"in-situ polymerization.Scanning electron microscope(SEM)was used to confirm the micropore structure of the column,and indicated the successful preparation of monolithic column.To study the chiral separation ability of?-CD-E2 amphoteric chiral selector,?-CD-E2column was applied to enantioseparation of two receptor antagonists:terazosin hydrochloride(TER),promethazine hydrochloride(PMZ);and two herbicides:imazethapyr(IMZR)and imazapic(IMZC).The separation conditions were optimized respectively.Under the same-length column and optimal conditions,the resolution of the TER was 124.42;The resolution of PMZ was 7.80,and the RSD values of the retention times of the two enantiomers were 1.08%and 1.94%,the RSD values of the peak heights of two enantiomers were 6.12%and 2.60%;The resolution of IMZR was 62.65,and the linear correlation coefficient r of the racemate concentration in the range of 6.2×10-66.2×10-5mol·L-11 with the peak heights and areas of two enantiomers were 0.9973,0.9576,0.9619 and 0.9087;The resolution of IMZC was 7.13,the linear correlation coefficient r of the racemate concentration in the range of 2.2×10-78.6×10-6mol·L-1 with peak areas of the two enantiomers were 0.9549 and 0.9357.The results showed that?-CD-E2 showed good chiral recognition ability for acid and basic compounds,so it was expected to become a new amphoteric chiral selective agent with wide application.To compare the difference between the amphoteric selective agent?-CD-E2 and the anionic selective agent bis[-6-(3-deoxycitrate monoester-4)]-?-CD(?-CD-B2)chiral separation ability,the enantioseparation of acidic herbicides 2,4-D propionic acid(DICP)and bentaquine(IMAN)was studied by?-CD-B2 column.The effects of buffer pH,applied voltage and buffer concentration were explored respectively,and the linear range and reproducibility were investigated.In the NaHCO3-citric acid buffer system,the resolution of DICP reached 3.77,and the linear correlation coefficient r of the racemate concentration in the range of 5.4×10-56.2×10-4mol·L-1 with the peak heights and areas of two enantiomers were 0.9335,0.9078,0.9962,and 0.9956,the RSD values of retention times of the two enantiomers were 2.05%and2.10%;Use the same column in Na2HPO4-citrate buffer system,the resolution of imazaquin was 78.19,the linear correlation coefficients r in the range of 1.6×10-69.7×10-6mol·L-1 with the peak heights and areas of two enantiomers were 0.9431,0.9057,0.9664,and 0.9457,and the RSD values of retention times of the two enantiomers were 13.84%and 7.15%.Meanwhile,combining the previous work of our group,the separation of IMZR and IMZC on two monolithic columns was compared.The results indicated that both chiral selectors showed good enantiomeric recognition ability for acid herbicides;Compared with?-CD-B2,?-CD-E2 had imidazole group outside the cavity,it can generate stronger interaction with IMZR and IMZC,resulting in higher separation efficiency.In summary,the results showed that?-CD-E2 contained carboxyl and amino groups,it had amphoteric qualities and can form strong interactions with acidic compounds that contained benzene rings and carboxyl groups in the chemical structure and had low pKa values.It can also generate strong electrostatic interaction with basic chiral molecules with nitrogen heterocycles.In this study,?-CD-E2,which had both acid and base characteristics,was used in the field of enantioseparation.It showed strong chiral recognition ability for both acidic and basic compounds,proving that?-CD-E2 was a promising chiral selector.The preliminary results showed that the monolithic column constructed by the amphiphilic derivative?-CD-E2 was different from the monolithic column?-CD-B2;Compared with anionic?-CD-B2 monolithic column,?-CD-E2 monolithic column was expected to be more applicable. |
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