Preparation And Evaluation Of Biligand Ionic Liquids Stationary Phases For Mixed-mode Chromatography

Currently,high performance liquid chromatography（HPLC）is one of the most widely used separation and analysis techniques.The stationary phases are the key to determining its separation function,and it is an important reason that directly affects the separation effect of substances.Therefore,the development of new stationary phases has always been a hot topic of high performance liquid chromatography.With the rapid development of separation science in the fields of pharmaceutical research,environmental monitoring,and food safety,traditional Single separation mechanism stationary phases are difficult to meet the separation of complex samples.As a supplement to single-mode stationary phases,mixed-mode stationary phases,can achieve multiple retention mechanisms on a single chromatographic column and has a wider range of applications.In recent years,ionic liquids（ILs）have been widely used in the development of stationary phases for high performance liquid chromatography due to their high thermal stability and easy modification.In this study,ionic liquids were used as the ligand,spherical porous silica gel was used as the stationary phase matrix,and four chromatographic stationary phases were prepared by the reversible addition fragmentation chain transfer polymerization and“thiol-ene”click reaction.The retention properties,retention mechanisms,and separation effects of the stationary phases were investigated and compared with commercial columns.The main work is as follows:（1）Preparation and application of a novel imidazolium C14 copolymer mixed-mode chromatographic stationary phase:Synthesis of a vinyl imidazolium benzoic acid and N-tetradecylacrylamide as functional monomers copolymerized to the surface of silica gel through reversible addition fragmentation chain transfer（RAFT）polymerization,and prepared a new type of imidazolium ionic liquid mixed-mode Stationary Phase.The new stationary phase was systematically characterized by Fourier-transformed infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）,thermogravimetric analysis（TGA）elemental analysis and Zeta potential analysis techniques.At the same time,the results of gel permeation chromatography（GPC）indicated the successful control of the polymerization reaction.The retention behavior was studied under different chromatographic conditions（acetonitrile content,buffer salt concentration,buffer p H and column temperature）.In order to further explore the retention mechanisms of the new stationary phase,the linear solvation energy relationship model was applied under different chromatographic conditions,and the interaction between solutes,stationary phases and mobile phases was further explored,and the effect of temperature on the retention mechanism was further studied through the Van’t Hoff plot.In addition,the prepared stationary phase can be used in reversed-phase chromatographic/hydrophilic interaction chromatographic/ion exchange chromatographic mode,and the benzene series,nucleoside bases,carboxylic acids and inorganic anions can be separated,and the commercial mixed-mode chromatography column used for comparison,and provided different retention options.Finally,the prepared chromatographic column was applied to the detection of melamine in the milk samples.（2）Preparation and evaluation of imidazolium ligand stationary phases in mixed-mode chromatography with different ratios of positive and negative charge:Two silane reagents,including a C9 imidazolium ionic liquid silane reagent and a C9 carboxylic silane reagent,were prepared by the photoinitiated“thiol-ene”click chemistry reaction.The silica gel was modified by one-step bonding method,and three ionic liquid stationary phases with different positive and negative charge ratios（1:3,1:1,3:1）were prepared and compared.Firstly,the influences of the acetonitrile content and p H of the mobile phase on retention were explored.The results proved that all the stationary phases exhibited the properties of mixed-mode stationary phases.The mixtures can be separated in reversed-phase mode and hydrophilic mode.Meanwhile,the mobile phase p H has obvious different effect in the retention of charged substances on the three stationary phases.To further explore the differences retention behavior between the three columns,the linear solvation energy relationship under different p H conditions was investigated.Finally,the benzene series were successfully separated on the chromatographic column prepared in this experiment,and the commercial XB-C18column was used for comparison.The nucleoside bases were separated on the preparative column and compared with the commercial APS-2 Hypersil^TM column to provide different retention selectivity.Five carboxylic acids,four basic and acidic substance mixtures are separated on three preparative columns,with good separation selectivity.The results showed that the chromatographic columns with different positive and negative charge ratios can separate acidic substances and alkaline substances.There are significant differences in effect and selectivity.