Investigation Of Phenylene-Bridged Hybrid Silica Packings For High Performance Liquid Chromatography And Surface Modifications Of Silica

Silica is the most widely used matrix material for high performance liquid chromatography (HPLC). The chemical stability of silica matrix and bonded phase decide whether a silica-based packing can be used in an extended pH range. Surface Chemical modification is significant for functionalization of silica matrix. In view of above aspects, following studies have been done in this thesis.1. Phenylene bridged organic/inorganic hybrid silica (PHS) spheres were prepared via sol-gel process using mixed silicon-source of1,4-bis(triethoxysilyl)benzene (BTEB) and tetraethoxysilane (TEOS). Pore-expanded materials were prepared via successive hydrothermal treatment with dodecylamine/N,N-dimethyldecylamine and Tris(hydroxyl-methyl)aminomethane. Influence of hydrothermal temperature and concentration of pore-expanding agent on pore structure was investigated. Four PHSs (PHS1/4, PHS1/2, PHS1/1, PHS2/1) with different content of phenylene moieties were prepared by using different ratio of BTEB and TEOS in the same condition. After packing them into chromatographic columns, the stability of PHS was evaluated under high pH (pH=11.0) condition. It is demonstrated that the alkaline stability is improved as the content of phenylene moieties increases.2. C18bonded reversed-phase (RP) stationary phases based on above mentioned PHS were prepared through silylation reaction with octadecyltrichlorosilane. The C18RP phase based on PHS2/1showed good stability. The column lasted for more than100hours at pH11.0without deteriotation of performance as measured by plate count and retention time. However, at low pH (pH=1.0) the stationary phase is still unstable, the retention capacity will decline due to the loss of organic ligands from silica surface by solvolysis and subsequent breaking the Si-O-Si bond.3. Two RP stationary phases which are stable both under high and low pH conditions were prepared based on direct modification of organic bridges in hybrid silica. The specific methods are:(1) a RP stationary phase with C-O-R bonding type was prepared by two-step reactions of successive demethylation and etherification;(2) another one with C-N(O)-R bonding type was prepared by three-step reactions of successive nitration, amination and amidation. Some ionic compunds were analyzed with acidic and alkaline eluent to illustrate the advantages of the improved chemical stability of these two packings.4. A serious chiral stationary phases (CSP), whose structure incorporate structures incorporate S-1,1’-binaphthyl moiety as the chiral selector and1,2,3-triazole ring as the spacer, were prepared via "click" chemistry reaction of Cu(Ⅰ)-catalyzed azidealkyne1,3-dipolar cycloaddition. These CSP showed good enantioselectivity for various BINOL and3-phenyl indolin-2-one derivatives. A comparation of two CSP which are having and lacking triazole ring linkage, indicates that the triazole ring linkage plays an important role, although it was remote from the chiral selector of the CSP.