Triazine-based Covalent Organic Polymers For High Performance Liquid Chromatography Stationary Phases With Core-Shell Structure

Covalent organic framework?COFs?have many advantages such as high thermal and chemical stability,large specific surface area,adjustable pore size,various structures and synthesis methods.These advantages make COFs show good application potentials in the field of separation.As the member of the COFs family,triazine-based covalent organic polymers?CTPs?are constructed of alternating hydrophilic triazine rings and lipophilic aromatic rings.In addition to the common advantages of COFs,the amphiphilic groups in the CTPs endow its hydrophilic-lipophilic balance?HLB?properties.In this article,by controlling the continuous Friedel-Crafts reactions on the surface of silica,a high performance liquid chromatography stationary phase with core-shell structure was prepared,its chromatographic separation performance and retention mechanism in reverse phase?RP?and hydrophilic interaction?HILIC?mode were investigated.The article was divided into three chapters:The research progress of CTPs as the member of the COFs family and the development status of liquid chromatography stationary phases were introducted in the first chapter,the materials have been widely used in chromatography stationary phases with the continuous development of COFs,then the significance of the topic selection and the main research content were discussed.In the second chapter,the triazine-based chromatography stationary phase SiO₂@CTP_CC-TPB with core-shell structure was synthesized by coating cyanuric chloride and1,3,5-triphenylbenzene on the surface of amino silica though continuous Friedel-Crafts reaction.The stationary phases of three shell thicknesses were obtained by controlling the feed ratio.A series of characterizations were carried out and the chromatographic performance of the stationary phase was investigated.It was found that the stationary phase could not only separate mono-substituted benzenes,anilines,polycyclic aromatic hydrocarbons?PAHs?and aromatic positional isomers,but also separated nucleoside and nucleic bases in the hydrophilic mode,which had RP/HILIC mixed mode.The study found that CTP_CC-TPB could provide a variety of action sites for the solute,and recognized the solute guest through various forces such as hydrophobicity,hydrogen bonding,?-?,and electron transferr,etc.The repeatability,stability and thermodynamic properties of the stationary phase were also investigated.Due to more aromatic and fewer polar moieties on SiO₂@CTP_CC-TPB,it had stronger retention for aromatics but weaker retention for polar compounds.A new stationary phase SiO₂@CHP_Cy-DB was prepared by the similar method which used heptazine rings with more nitrogen atoms and diphenyl with fewer benzene rings as organic building blocks in the third chapter.The study of SiO₂@CTP_CC-TPB with chromatographic performance indicated that the stationary phase had PR/HILIC mixed mode.In order to compare the hydrophilicity of SiO₂@CHP_Cy-DB and SiO₂@CTP_CC-TPB,the separation of cytosine and uracil on two columns was investigated.The results showed that both SiO₂@CHP_Cy-DB and SiO₂@CTP_CC-TPB2 all had good hydrophilicity,and the hydrophilicity of the two phases showed the phenomenon of alternating strength and weakness under different mobile phases.