The Construction Of High Performance Capillary Electrochromatography Methods Based On Covalent Organic Frameworks And Their Applications

Capillary electrophoresis(CE)is a versatile analytical method that is widely used in various fields for the separation and analysis of numerous substances such as biological macromolecules,neutral molecules,and organic small molecules.Based on the different nature of analytes and detection requirements,researchers have developed different CE separation modes,including capillary electrochromatography(CEC),capillary gel electrophoresis(CGE),capillary zone electrophoresis(CZE),capillary micellar electrokinetic chromatography(MECC),etc.In open-tubular capillary electrochromatography(OT-CEC),the stationary phase is coated on the inner wall of the capillary by physical adsorption or chemical bonding,which has the advantages of simple operation,good permeability,high reproducibility and stable electroosmotic flow,and has been successfully applied in various fields such as food analysis,drug analysis and chiral separation.The exploration of suitable stationary phases is the core topic of OT-CEC.Recently,various porous nanomaterials have been developed as OT-CEC stationary phases,such as graphene oxide,magnetic nanoparticles,metal organic framework materials(MOFs),porous organic polymers,molecular cages,and covalent organic framework materials(COFs).However,the relatively low phase ratio of open-tubular columns leads to the need for further improvement of OT-CEC separation performance.COFs are an emerging class of crystalline porous polymers with highly tunable structures and functions.COFs have promising applications in analytical fields,especially in chromatographic separations,due to their superior properties such as low density,excellent stability,high specific surface area,and easily adjustable pore size and chemical environment.So far,researchers have prepared COFs-coated columns mainly by post-modification and in-situ growth methods,among which,open-tubular columns prepared by in-situ growth method at room temperature have the advantages of uniform and dense coating,high separation capacity,long lifetime,high stability and reproducibility,which have greatly promoted the development of OT-CEC method.However,there is a relative lack of research on the separation mechanism of COFs as stationary phase,for example,the relationship between the linkage type,morphology and specific surface area of COFs and their separation performance has rarely been reported.Based on this,the following three works was carried out in this thesis.(1)Imine COFs are characterized by easy monomer modification,mild synthesis conditions and controllable size with abundant N and O sites,which can generate multiple interactions with analytes and are beneficial for their application in OT-CEC.Therefore,in this work,the imine TPB-DMTP COF was introduced into the capillary inner wall for the first time by the in-situ growth method,and the coated capillary was characterized in detail.The results showed that TPB-DMTP COF has been successfully synthesized and immobilized on the inner wall of the capillary.Meanwhile,the OT-CEC method based on this coated capillary as the separation channel has excellent separation performance for phenylurea herbicides,polybrominated dibenzofurans flame retardants and phenol compounds.In addition,the TPB-DMTP COF-coated capillary has excellent reproducibility and stability.Based on this,the proposed new OT-CEC method has been successfully used for the determination of four herbicide residues in real samples including Yellow River water,soil,Chinese cabbage,apple and cherry tomato.(2)COFs have high specific surface area and are ideal stationary phases for chromatography.However,until now,no studies on the surface area of COFs in relation to their separation performance have been reported.Therefore,in this work,four imine-based TPB-DMTP COF-coated capillaries with different specific surface areas were prepared for the first time by adjusting the amount of catalyst(acetic acid)by in-situ growth method at room temperature.The broad-spectrum separation performance and stability of the coated capillaries were investigated and evaluated by using the TPB-DMTP-0.4 COF-coated capillaries as a model and selecting six groups of analytes,including acidic,basic and neutral compounds.In addition,the influence of specific surface area of COFs materials on their separation performance was investigated in depth,and the results showed that the stationary phase with too large or too small specific surface area was disadvantaged to the separation process,which provided a new idea for the rational design of chromatographic stationary phase and was of great significance for the preparation and application of COFs coated capillary.(3)In this work,a new TPB-TP COF-coated capillary was successfully prepared by in situ growth method and applied to OT-CEC separation for the first time.TPB-TP COF with high hydrophobicity and large π-conjugated structure was successfully used as OT-CEC stationary phase for the separation of four groups of neutral compounds.Compared with the bare capillary column,the TPB-TP COF-coated column showed better separation ability for the four groups of neutral analytes.In addition,the TPB-TP COF-coated capillaries exhibited satisfactory reproducibility and stability.Based on the excellent separation ability of TPB-TP COF-coated capillary,a new OT-CEC method for the separation of phthalate esters(PAEs)was established and has been successfully used to the determination of PAEs in Yellow River water sample.