| Metal-organic frameworks(MOFs), a kind of noval functional microporous materials being widely researched recently, have great potential for applications in chromatography due to their porous structures and unique properties. Compared with the effort on the exploitation of GC separation, the study of high performance liquid chromatography(HPLC) separation in MOFs is still at the early stage due to the poorly chemical stability in MOFs. Herein, it is necessary for the synthesis of MOFs with excellent chemical stability, which has a great potential and big space for further exploration in HPLC application.Ui O-66 type MOFs, based on robust inorganic Zr6O4(OH)4 clusters, exhibit excellent chemical/thermal stability, large surface area, and two types of cages, which make them good candidates in acting as stationary phase in HPLC separation. In this study, three Ui O-66 type frameworks, including parent [Zr6O4(OH)4(BDC)6](Ui O-66), amino-functionalized [Zr6O4(OH)4(BDC-NH2)6](Ui O-66-NH2), linker-lengthened [Zr6O4(OH)4(BPDC)6](Ui O-67), were successfully synthesized and further studied for their applications in HPLC separations of substituted benzenes(SBs) and polycyclic aromatic hydrocarbons(PAHs). In addition, the associated possible mechanisms have been also proposed. The main research and results of this thesis are listed as follows:(1) Three Ui O-66 type MOFs: Ui O-66, Ui O-66-NH2, and Ui O-67 were obtained by solvothermal condition and characterized by PXRD, TGA, N2 adsorption-desorption, and scanning electron microscope(SEM).(2) Ui O-66, Ui O-66-NH2, and Ui O-67 packed columns(5 cm long, 4.6 mm i.d.) were prepared for the following HPLC separations through “wet method of packing column” under high pressure.(3) Ui O-66 was used as the stationary phase for RP- and NP-HPLC separations of SBs and PAHs. It shows that the mobile phase composition plays an important role in the HPLC separations, and the baseline separations of some analytes on Ui O-66 packed column were achieved by controlling the mobile phase composition. The reverse shape selectivity, size selectivity and stacking effect based on the MOFs cages and van der Waals force between analytes and the stationary phase also play vital roles in the separations of these analytes. Other critical HPLC parameters, such as injected sample mass and column temperature were also evaluated. It was confirmed that the separation of SBs on Ui O-66 packed column is an exothermic process, controlled by both enthalpy change(?H) and entropy change(?S). The reliability studies indicate that the Ui O-66 packed columns have a good reproducibility and stability with the relative standard deviations(RSD) of retention time, peak height, peak area, and half peak width for the five repeat separations of the analytes are within 0.2-0.4%, 0.2-1.6%, 0.7-3.9%, and 0.4-1.1%, respectively.(4) Using Ui O-66-NH2 as stationary phase for RP- and NP-HPLC separations of SBs and PAHs, we evaluated some parameters influencing the HPLC separation, such as mobile phase composition, injection mass, and column temperature. The NP-HPLC separation of EB, styrene, and o-xylene on Ui O-66-NH2 packed column was confirmed to be an exothermic process. Also, the separations of these analytes on this column show excellent reproducibility with the RSD of retention time, peak height, peak area, and half peak width less than 1%. By comparing with the NP-HPLC separation on Ui O-66, it is easy to conclude that the existence of-NH2 in the structure of Ui O-66-NH2 indeed leads to the change of physical and chemical environment and spatial pattern of the cages, which results in the interaction change between analytes and the mobile phase, and finally significantly influences the chromatographic separations.(5) Ui O-67 was used as stationary phase for the NP-HPLC separations of SBs and PAHs. It shows that SBs with smaller kinetic diameter have no retention on Ui O-67 stationary phase and the mobile phase composition has almost no effect on their separations, while PAHs with larger kinetic diameter could be retained strongly on it and the ratio of hexane/DCM significantly affected their separations. Some PAHs molecules can achieve baseline separation on Ui O-67 packed column within a short time by controlling the mobile phase. By comparing with the NP-HPLC separation using Ui O-66, which has smaller cages, as the mobile phase, we concluded that the pore size of a MOF structure plays a vital role in the separation, which may be the possible explanation for SBs and PAHs separations on Ui O-67 stationary phase. |
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