Fabrication and evaluation of stationary phases with different morphology from two imidazole-based ligands for nonchiral and chiral electrochromatographic separation.

In this work, two metal-organic porous materials from the two imidazole-based ligands (4-methylimidazole-5-carbaldehyde (aImeIm) and histidine (His)) and the same metal source (Zn(CHCOO)·2HO), namely His-ZIF-93 with a crystal zeolite imidazolate framework and His/aImeIm@Zn with an amorphous networks, were first designed and synthesized by the one-pot method. They were used as the stationary phases (SPs) of open-tubular capillary electrochromatography (OT-CEC) to evaluate and compare their separation performance for the nonchiral and chiral compounds. His-ZIF-93-bonded OT-CEC column successfully separated five families of nonchiral analytes due to the synergistic effect of His and the crystal framework. The separation mechanism included electrostatic interaction, molecular sieve effect, π-π interaction, electrophoretic mobility, hydrogen bonding interaction, and so on. His/aImeIm@Zn-bonded OT-CEC column exhibited a more superior enantioseparation capability for seven chiral compounds with an ultrahigh column efficiency of 7.6 × 10 plates/m due to a large number of chiral sites and the porous networks. Enantioseparation were attributed to the difference of adsorption and selectivity between the SPs and the two enantiomers through the adsorption experiments and the binding constants tests. Thus, both His-ZIF-93-bonded OT-CEC column and His/aImeIm@Zn-bonded OT-CEC column demonstrated the universality for the analytes, as well as excellent reproducibility, satisfactory stability and long lifetime.