Preparation And Characterization Of The Open-tubular Capillary Electrochromatography Column Based On Zeolite Imidazolate Frameworks

Open-tubular capillary electrochromatography（OT-CEC）column has attracted extensive attention due to its easy preparation,low backpressure and high column efficiency.The disadvantage of open-tubular column is that the column capacity and phase ratio were low.Therefore,the key to preparing an open-tubular column is to increase its surface area.Metal organic frameworks（MOFs）have the advantages of large specific surface area,high porosity,adjustable pore size and excellent stability.Therefore,they have attracted widespread attention as stationary phases for CEC.Polydopamine（PDA）can be easily deposited on virtually all types of inorganic and organic substrates,with controlled film thickness and durable stability.In this paper,MOF-5 and ZIF-67 were fixed to the inner wall of the capillary using various properties of PDA to prepare MOF-5-PDA and ZIF-67-PDA electrochromatography columns.The separation performance of the two electrochromatography columns for Polycyclic aromatic hydrocarbons（PAHs）were researched.The main contents are as follows:MOF-5 and ZIF-67 crystal materials were prepared by solvothermal method and characterized by FT-IR,TG,SME and XRD.The results of FT-IR and XRD spectrum are consistent with those reported in the literature,indicating that MOF-5 and ZIF-67crystal materials were successfully prepared.SEM results showed that the size of the prepared MOF-5 crystal was 10-15μm,and the size of the ZIF-67 crystal was about 2μm.TG results show that both MOF-5 and ZIF-67 have good thermal stability.A mussel-inspired polydopamine functionalization method was used for fixed MOF-5 to the inner surface of the capillary.First,PDA was deposited on the inner surface of the capillary using the property that dopamine can self-assemble to form a PDA under alkaline conditions.Secondly,MOF-5 was immobilized on the inner surface of the capillary using the adhesive property of PDA（involving covalent and non-covalent binding）and chelating activity to Zn²⁺.SEM characterization confirmed the successful fixation of MOF-5 to the inner surface of the capillary.PAHs were selected as target analytes to research the separation performance of MOF-5-PDA electrochromatography columns.The effects of acetonitrile content,buffer solution concentration and buffer solution p H on the separation were investigated.The experimental results show that when the content of acetonitrile in the buffer solution is 40%,the concentration of the buffer solution is 20 m M,and the p H of the buffer solution is 8.5,baseline separation of seven PAHs was achieved.The relative standard deviations（RSD）of retention time and peak area for intra-day,inter-day and column-to-column were less than 5%,indicating that the MOF-5-PDA electrochromatography column has good stability.A bio-inspired polydopamine functionalization method was used for fixed ZIF-67to the inner surface of the capillary.First,the dopamine can be self-assembled to form polydopamine under alkaline conditions and the polydopamine was deposited on the inner surface of the capillary.Secondly,ZIF-67 was immobilized on the inner surface of the capillary using the adhesive property of PDA（involving covalent and non-covalent binding）and its chelating activity to Co²⁺.SEM characterization confirmed the successful fixation of ZIF-67 to the inner surface of the capillary.PAHs was selected as target analytes to research the separation performance of ZIF-67-PDA electrochromatography columns.The effects of acetonitrile content,buffer solution concentration and buffer solution p H on the separation were investigated.The experimental results show that when the content of acetonitrile in the buffer solution is 30%,the concentration of the buffer solution is 20 m M,and the p H of the buffer solution is 8.5,the baseline separation of the seven PAHs was achieved.The RSD of retention time and peak area for intra-day,inter-day and column-to-column were less than 6%,indicating that the stability of the ZIF-67-PDA electrochromatography column was good.