Post-synthetic modification of NH2-MIL-101(Al)@SiO2 with different non-polar ligands for improving HPLC separation performance of estrogens

Due to the excellent pore structure, MOFs as the stationary phase was playing an important part in chromatography. In this work, the shell-core MIL-101(Al)@SiO2 composites post-synthetic modified by ligands with different polarities were fabricated for separation of estrogens. The structure and morphology of these materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET). In order to investigate the influence of the ligand polarity on chromatographic separation performance of estrogens, alkyl molecules with different chain length were introduced as the ligands. With the hydrophobicity and chain length of the ligands increasing, the resolutions of the MIL-101(Al)@SiO2 columns for the separation of estrogens exhibited the tendency of a parabola. Best result was achieved on the C4-MIL-101(Al)@SiO2 column. On that basis, the possible retention mechanism on C4-MIL-101(Al)@SiO2 column was elucidated by studying the mobile phase effect on separation behavior.