Enantiomeric Separation of Chiral Triazole Pesticides by a mono-6-(4-Nitrophenyl)-ureido-β-cyclodextrin-Bonded Stationary Phase Using High-Performance Liquid Chromatography
A mono-6-(4-nitrophenyl)-ureido-β-cyclodextrin-bonded chiral stationary phase (NCDSP), containing π-electron withdrawing groups, was prepared by immobilizing a self-prepared mono-6-(4-nitrophenyl)-ureido-β-cyclodextrin ligand onto ordered mesoporous silica gel SBA-15, on which the ligand was synthesized by the reaction of mono-6-amino-β-cyclodextrin with 4-nitrophenylisocyanate. The structure of NCDSP was characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis and solid nuclear magnetic resonance. The introduction of electron-withdrawing (π-acidic) groups facilitated the separation of the π-electron-rich (π-basic) triazole chiral pesticides. In addition, the ureido group linkage allowed NCDSP to be a hydrogen bond-accepting and -donating chiral station phase and prevented the hydrolysis associated with nitrobenzoate and nitrophenylcarbamate linkages. As a result, the enantioseparations of nine triazole pesticides were achieved using NCDSP. Meanwhile, the chromatographic conditions, such as the pH and the composition of mobile phases, were investigated in detail. Moreover, in a comparative study with a cyclodextrin stationary phase (CDSP), the NCDSP provided higher enantioselectivity. Baseline separations for most of these triazoles on NDCSP were observed in relatively short times from 10 to 20 min. The highest resolution achieved was 2.87. Otherwise, incomplete enantiomeric separation was observed on the CDSP with a maximum resolution of less than 1.18. For the NCDSP, in addition to the inclusion effect, the π-π interaction between the electron-deficient stationary phase and the electron-donating triazoles significantly contributed to the chiral separation. This work reports a simple and convenient method for the preparation of the NCDSP with the rapid separation of chiral triazole pesticides.
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