Research On Surface Modification Of Silica-based Stationary Phases

As a keynote of high performance liquid chromatography?HPLC?,the stationary phase directly affects the final separation performance.The matrixs of stationary phases are divided into three groups,which are silica?silica,SiO₂?,polymer and metaloxide.Because SiO₂ has the characteristics of high mechanical strength and chemical stability,easy modification in addition to its controllable particle size,pore size and surface area,it is the most widely used.There are many hydroxyl groups on the surface of SiO₂,which makes it easy to be modified through chemical bonding.However,SiO₂-based stationary phases still have two major limitations:peak tailing of basic analytes due to interactions with residual silanol groups and poor chemical stability in mobile phases outside of the pH 2-8 range.Thus,to enhance HPLC performance,it is important to improve chemical stability and lower silanol activities.In addition,with the rapid development of health care,disease surveillance,food hygiene,environmental monitoring,samples to be separated become complex.Therefore,the single-mode chromatography may be not sufficient to meet the separation and analysis demand.As a complementary mode,mixed-mode chromatography?MMC?,based onmultiple retention mechanisms for the analytes,is characterized with good selectivity,high loading capacity and low cost.Therefore,the development of MMC stationary phases has become a research hotspot.With"modification of SiO₂ surface"as the subject,the thesis focused on developing a novel MMC stationary phase and decreasing acidity on SiO₂ surface.It mainly covers the following three parts:1.A novel MMC stationary phase,C18-DTT?dithiothreitol?SiO₂,was prepared through“thiol-ene”click chemistry.Chromatographic performance of the C18-DTT-SiO₂ was systemically evaluated by studying the effect of acetonitrile content,pH,buffer concentration of the mobile phase and column temperature.It was demonstrated that the novel stationary phase possessed reversed phase liquid chromatography?RPLC?/hydrophilic interaction liquid chromatography?HILIC?mixed-mode property.The application of C18-DTT-SiO₂ column was demonstrated in the separation of non-steroidal anti-inflammatory drugs,aromatic carboxylic acids,alkaloids,nucleo-analytes and polycyclic aromatic hydrocarbons.The results reveal that it had great potential in the analysis of various compounds and was a promising RPLC/HILIC MMC stationary phase.2.To lay the foundation for study on low peak-tailing or no peak-tailing of basic analytes stationary phases,feasible methods to shield the acidic silanols on the silica surface were developed.Via liquid deposition method,?i?tetraethyl orthosilicate?TEOS?;?ii?TEOS with?3-glycidoxypropyltrimethoxysilane?trimethoxysilane?GOPS?;?iii?TEOS,GOPS with a cation surface active agent,cetyltrimethyl ammonium bromide were separately used to modify SiO₂ surface.Nitrogen adsorption/desorption method was applied to characterize porous structure,and chemical titration was to determine the amount of silanols on the SiO₂.The results disclose that the pore size,pore volume and amount of silanols became smaller after these three modificcation.It demonstrated that these methods could shield silanols from SiO₂ to decrease its acidity,and the better shielding effect of last two methods was observed.3.The characterization of stationary phases for MMC in recent years was reviewed and the future development directions were outlined.