Silanol bonding technology

The IUPAC Compendium of Chemical Technology defines Normal Phase as an elution procedure in which the stationary phase is more polar than the mobile phase . In practice, the most widely used stationary phases for preparative HPLC are based on silica and the polarity of the underlying silyl ether and silanol provides the required hydrophilic surface. Amino and cyano bonded silica are also commonly used in normal phase mode though the latter also has some reversed phase properties. The predominant mechanism of interaction is hydrogen bonding. However, the silanol is mildly acidic so the silica surface will also have mild cation exchange properties. 

The selectivity of a separation is not only a function of the type of the bonded phase but can also depend on the spacing of the bonded-phase chains and the availability and activity of residual silanols. If we want to achieve highly reproducible separations, it is therefore very important that the composition of the stationary phase be tightly controlled. Luckily, the technology for preparation of silica-based bonded phases is now over 20 years old, and manufacturers have had ample time to learn to measure and control the important properties of bonded phases. 

Silica is one of the most popular mineral filler used in mbber technology. Three types of silica can be distinguished and namely precipitated, fumed and surface-modified silica. As an amorphous material with randomly placed functional silanol groups (Fig. 12.1), it readily generates hydrogen bonds with surrounding molecules [4]. 

The immobilisation of optically active alkenes on the silica surface by combined hydrosilation and sol-gel technology has been studied. The silanol and silyl groups in silicas which have been silylated with Cg chains have been estimated by Si NMR spectroscopy. Dehydroxylation and silanisation of the surfaces of sihca have been investigated. A A1 and Si NMR study of silane surface modified calcined kaolin has been reported. C NMR spectroscopy has been used to establish the bonding trihydrosilane to Ti02 particles. ... 

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