PHYSICO-CHEMICAL PROPERTIES OF COLLOIDAL SILICA WITH RELATION TO ITS APPLICATIONS IN PHARMACEUTICAL SYSTEMS
Abstract
Colloidal silica was studied with respect to its physicochemical and biological properties of pharmaceutical interest. Those properties, pertinent to the application of colloidal silica as a surgical glove lubricant, and stabilizing adjuvant in compressed aspirin tablets were emphasized. The following results were obtained. The water vapor adsorption properties of the silica were studied under various vapor pressure conditions (from 0 to 100 per cent relative humidity) at 40(DEGREES)C. and an adsorption isotherm was constructed. The silica exhibited adsorption behavior characteristic of adsorbents with limited pore volume. Treatment of the data in terms of the B.E.T. adsorption isotherm allowed the monomolecular layer volume ((chi)(,m) = 0.115 cc./gm. of SiO(,2)) and specific surface area of the silica (0.3276 meters('2) per gram) for water vapor adsorption to be determined. Such results were also obtained from a nitrogen adsorption isotherm; the monolayer volume and the specific surface were found to be 163.115 cc and 714.4 square meters per gram of silica. The results, although similar to those of other investigators, demonstrated superior water adsorption properties and a larger surface area for one of the types of colloidal silica studied. This silica material was chosen for further study with respect to its ability to affect the stability of a hydrolyzable drug in compressed tablets. The commonly employed method of assay for salicylic acid as a decomposition product for aspirin, was found to be inaccurate as an index of the degree of degradation of aspirin in compressed tablets at elevated temperatures, due to the loss of salicylic acid through sublimation. The sublimation was further studied and an activation energy of 19.327 Kcal/mole. determined. This allowed the prediction of the zero order rate at any temperature. Aspirin did not sublime at the temperatures studied, 40-70(DEGREES)C. The sublimation problem was circumvented by the development of a new spectrophotometric assay procedure for residual aspirin. It involved absorbance measurements at 262 and 296.5 m(mu). The assay method was verified and was found to be accurate within (+OR-) 1%. The stability of aspirin-silica tablets was determined at an elevated temperature and humidity condition (40(DEGREES) and 81.7 per cent relative humidity). It was found necessary to control tablet void volume, which was estimated from the volume of the tablet and the densities of its constituents. . . . (Author's abstract exceed stipulated maximum length. Discontinued here with permission of school.) UMI
Degree
Ph.D.
Subject Area
Pharmaceuticals
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