Synthesis of a nonpolar, chemically bonded stationary phase with low residual hydroxyl group content

A microporous silica support, LiChrosorb Si-100, has been silanized with octyldimethylchlorosilane and octylmethyldichlorosilane. The repeatability of the silanization procedure was within about 2%. In general, these nonpolar modified silicas still contain too many residual hydroxyl groups, causing bifunctional behaviour of the adsorbent. A partial condensation of surface silanol groups at a drying temperature >200°C, prior to the chemical modification, decreases the residual hydroxyl group content. With respect to this residual polarity, monochlorosilanes appear to be effective. The concentration of bonded octyl chains remains virtually constant up to a drying temperature of 400°C. Owing to silanization, the specific surface decreases by 15–20%, whereas the pore volume decreases by 25%.