Functionalization Of Organic-Inorganic Hybrid Silica And Its Application In Liquid Chromatography

Organic-inorganic hybrid mesoporous silica material has great potentials as stionary phase for high performance liquid chromatography?HPLC?due to their high surface area,desirable pore structure,tunable particle size,excellent mechanical stability and excellent chemical stability.In this paper,C₁₈-bonded ethyl-bridged organic-inorganic hybrid mesoporous silica was prepared via co-condensation and post-grafting method,respectively,under alkaline conditions by using silsesquioxane?1,2-bis?triethoxysilyl?ethane,BTESE?as precusor,dodecyltrimethylammonium bromide?DTAB?as structure-directing agent and octadecyltriethoxysilane?ODTES?as silylation agent.The chromatographic packing was deactivated via gas-solid reaction method by using hexamethyldisilazane?HMDS?as capping agent.The effect of the introduction of ODTES on the morphology,pore structure and surface modification of the samples was investigated in detail.The morphology,pore structure,mesoscopical ordering,hydrophobic property,thermal property and chemical composition of organic-inorganic hybrid silica spheres were characterized by means of scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,nitrogen adsorption-desorption,X-ray power diffraction?XRD?,water contact angle measurement,thermogravimetric analyses?TGA?,elemental analysis,solid state ¹³C cross-polarized magic angle spinning nuclear magnetic resonance(¹³C CP MAS NMR)and ²⁹Si magic angle spinning nuclear magnetic resonance(²⁹Si MAS NMR),respectively.The chromatographic separation performance of hybrid silica was evaluated and the effect of end-capping on the chromatographic performance was also investigated in detail.Prepared by co-condensation method,the organic-inorganic hybrid mesoporous silica microspheres with an ODTES/BTESE molar ratio of 0.08 exhibits a desirable pore structure,with a surface aera of 351.82 m²g^-1,a pore volume of 0.21 cm³g^-1 and a pore size of 3.72 nm.The carbon content of the sample reaches 25.36%.When used as stionary phase for HPLC,the sample realizes a baseline separation for a mixture of five compounds?uracil,phenol,pyridine,1-naphthylamine and naphthalene?.After exposed to the alkaline mobile phase at elevated temperature for 80 h,the column maintains more than 90%of its efficiency?the plate number of toluene?,exhibiting a high degree of resistance to alkali.End-capping by HMDS leads to a decrease of the concentration of surface hydroxyl groups from 6.63 to 4.57 mmol·g^-1.For the end-capped stionary phase,the above mixture can be more efficiently baseline-separated and the relative retention factor?of pyridine and phenol increases from 0.493 to 2.009.Prepared by post-grafting method,the organic-inorganic hybrid mesoporous silica microspheres with an ODTES/[Si]molar ratio of 0.6 exhibits a desirable pore structure,with a surface aera of 371.75 m²g^-1,a pore volume of 0.35 cm³g^-1 and a pore size of 4.63 nm.The carbon content of the sample reaches 22.27%.A mixture of six compounds?uracil,aniline,benzene,ethylbenzene,Tert-butylbenzene and N-butylbenzenecan?can be baseline-separated by the chromatographic packing prepared by post-grafting method.The plate number of toluene remains constant at about 90%after exposing the column to alkaline mobile phase at elevated temperature for 80 h,indicating that the stionary phase is chemically stable under basic conditions.The above mixture can be baseline-separated more efficiently by the end-capped stationary phase and the relative retention factor?of pyridine and phenol increased from 0.445 to 2.866.