Preparation And Characterization Of Functionalized C₁₈ Reversed Phase Silica Gel Packing

Functionalized reversed phase silica gel packing is widely used in the field of biology, chemistry and pharmaceutical industry etc. And Octadecyl-silylated silica is the most widely used material. Chlorosilane-silica bonded phase was prepared directly from the reaction of octadecyltrichlorosilane and silica. And ester-Cig silica bonded phase was prepared indirectly using the silane coupling agent as intermediate. The separating effect of silica gel packing is correlative with the organic content of the product. The effects of different experimental conditions on the organic content of bonded phases were studied. Chemical analysis, infrared spectroscopy (IR) and differential thermal analysis-thermal gravity analysis (TG-DTA) were employed to characterize the properties of the products.Ester-C18 silica bonded phase was prepared from the reaction of stearic acid and silica gel by using silane coupling agent γ-glycidoxypropyltrimethoxysilane as intermediate. The silica bonded phase was characterized by IR. The result showed that the peaks at 2927.23cm~-1 and 2856.52cm~-1 were -CH2- stretching vibration. The peak at 1741.42 cm~-1 represented stretching vibration of the ester bonded. The organic content of packing was characterized by TG-DTA. Influences of silica pretreatment, reaction time, silane coupling agent dosages and catalyst were evaluated. The results showed that the best way of pretreating the silica gel was dipping in acid after ultrasonication; The most feasible reaction time was 10-12 hours; The optimum dosage of the silane coupling agent was lmL/(lg silica) and diethylamine was the best catalyst to accelerate the reaction. The organic content of the product decreases with increasing the heat-treating temperature of silica gel and increases with silica specific surface area increasing. The experiment reproducibility was excellent.Chlorosilane-C18 silica bonded phase was prepared from silica and octadecyltrichlorosilane. The result of IR showed that the peaks at 2927.78 cm~-1and 2856.88 cm~-1were -CH2- stretching vibration. The organic content was mensurated by TG-DTA, and the result indicated that the best way of pretreating the silica gel was dipping in acid after ultrasonication. Churning at room temperature was better than heating and circumfluence. The most feasible reaction time was 2 hours and the most feasible dosage of chlorosilane was 0.4mL/ (lg silica). The catalyst accelerated the reaction obviously. The organic content of the product declines with increasing the temperatur-e on silica gel and increases with silica specific surface area increasing. The experiment reproducibility was excellent.The amount of silanols on the silica gel and silica bonded phase was determined by chemical titration.The relation between the amount of silanols and the specific surface area was discussed.The relation between reactive silanols and the organic content of the resulting product was also discussed. The results on the heat-treating analysis showed that the amount of silanols on the silica gel has a linear relation with the specific surface area, and the organic content of the product also has a linear relation with the number of the reactive silanols. The results on different particle size showed that the amount of silanols on the silica gel has a linear relation with the specific surface area, and the organic content of the product was directly proportional to the number of the reactive silanols.The evaluation of Cis reversed silica bonded phase packing included the determination of impurity content, the examination of the sorption to pigment and the separation of standard substance. It was shown that chlorosilane silica bonded phase is pure and identical with Merck product. Ester silica bonded phase is inferior than Merck product and may be improved by washing. The examination of the sorption to pigment indicated that chlorosilane silica bonded phase is similar with Merck product and ester silica bonded phase is inferior to Merck product. It was shown that the standard substances were separated very well on chlorosilane silica bonded phase and ester silica bonded phase, and the separation was comparable with Merck product.