Preparation And Chromatographic Performance Of Mixed-mode Silica Stationary Phase Modified By Double Cationic Ionic Liquid And Octadecyl Group

As a widely used separation analysis and purification technology,high performance liquid chromatography plays an irreplaceable role in many fields such as life science,material science,food science and environmental science.The stationary phase of liquid chromatography is not only a decisive factor for chromatographic separation performance,but also an important reason that directly affects the separation effect of substances.Therefore,the development of new stationary phases for high performance liquid chromatography has always been a research hotspot.In recent years,single separation mode liquid chromatography has developed rapidly due to its high sensitivity,high selectivity and high separation ability.However,with the continuous increase of sample complexity,single separation mode chromatography technology gradually exposed its limitations.In recent years,the mixed separation mode chromatography technology has emerged.It has the characteristics of adjustable selectivity,high resolution,and large sample load.It can realize multiple separation mechanisms on the same chromatographic column,and has great potential in the separation and analysis of complex samples.So the development of mixed-mode chromatography stationary phase has become the focus of new stationary phase research.Ionic liquids are widely used in the research of mixed-mode chromatography stationary phases because of their unique physicochemical properties such as low melting point,high selectivity,and low vapor pressure,as well as their strong designability.In this paper,a mixed-mode silica stationary phase was prepared by step-by-step bonding,using spherical porous silica gel as the stationary phase matrix,dicationic ionic liquid and octadecyl long chain as ligands,and characterized and systematically chromatographic performance evaluation.This paper mainly includes the following research contents:1.Synthesis and characterization of 1,5-bis（imidazol-1-yl）pentane monomer: It was characterized by nuclear magnetic resonance spectroscopy and liquid chromatography-quadrupole time-of-flight mass spectrometry,and the results showed that1,5-bis（imidazol-1-yl）pentane monomer was successfully synthesized with high purity.2.Preparation and characterization of dual-cationic ionic liquids and octadecyl-modified mixed-mode silica stationary phases: modification of long-chain octadecyl and 1,5-bis（imidazol-1-yl）pentane by nucleophilic substitution,respectively A new type of mixed-mode silica chromatography stationary phase with bicationic ionic liquid and long carbon chain as ligands was prepared.The modified functional groups on the stationary phase matrix were characterized by Fourier transform infrared spectroscopy,and the results showed that the dicationic ionic liquid and octadecyl group were successfully modified.The functional groups modified on the stationary phase matrix were qualitatively and quantitatively characterized by elemental analyzer,and the results showed that the ligands were successfully modified to the stationary matrix and capped successfully at each stage.The specific surface area of activated silica gel and mixed-mode silica gel chromatography stationary phase modified by imidazolyl double cationic ionic liquid and octadecyl was measured and calculated by the BET specific surface area test method of physical adsorption instrument.Changes in surface area and pore structure were characterized.The results show that the specific surface area of silica gel decreases and the pore structure is filled with the increase of ligand bonding amount.3.The synthesized dicationic ionic liquid and octadecyl-modified mixed-mode chromatographic stationary phase were packed into a chromatographic column,and the retention mechanism of the chromatographic column was explored by changing the water content,salt concentration and organic phase type in the mobile phase.It was found that under certain conditions,the column can be performed in hydrophilic chromatography（HILIC）,reversed-phase chromatography（RPLC）and reversed-phase/hydrophilic hybrid chromatography（RPLC/HILIC）.Hydrophilic base nucleosides were used to evaluate the separation performance of the packing in HILIC mode.Hydrophobic substances such as naphthalene were used to evaluate the separation performance of the packing in RPLC mode.The separation performance in RPLC/HILIC mode was evaluated using mixed polar compounds including hydrophilic and hydrophobic compounds.Excellent separation effect was obtained.In addition,the separation stability and repeatability of the column were verified by repeatable experiments and satisfactory results were obtained.