Bonded stationary phases condensation process

The hydrogel is allowed to stand for a few days during which time a process called sinerisis takes place. During sinerisis the condensation of the primary particles, one with another, continues and the gel shrinks further, accompanied by the elimination of more saline solution that exudes from the gel. After three or four days, sinerisis is complete and the gel becomes firm and can now be washed free of residual electrolytes with water. The washed product is finally heated to 120°C to complete the condensation of the surface silanol groups between the particles, and a hard xerogel is formed. It is this xerogel that is used as the LC stationary phase and for bonded phase synthesis. It is not intended to discuss the production of silica gel in detail and those interested are referred to "Silica Gel and Bonded Phases", published by Wiley (1). 

Sol-gel is basically a synthetic glass with ceramiclike properties. The processing consists of hydrolysis and condensation of a metal alkoxide (i.e., tetraethoxysilane) to form a glassy material at room temperature. Further modification of this material with a polymer (stationary phase) is used to prepare phases for capillary columns there has been keen interest in this process (118-123). The final sol-gel product retains the properties of the polymer as well as the properties of the sol-gel component. The sol-gel material is able to covalently bond to fused silica. 

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