DETERMINATION AND IDENTIFICATION OF THE PHYSICO-CHEMICAL PROPERTIES OF SODIUM BICARBONATE RELATED TO THE CHEMICAL STABILITY OF PHARMACEUTICAL EFFERVECENT SYSTEMS
Abstract
A new analytical procedure specifically designed for the determination of moisture content in sodium bicarbonate was developed. While gravimetric methods have not been able to be used in the past for materials such as sodium bicarbonate which effloresce on heating, a procedure was developed which measured the efflorescence (spontaneous CO(,2) loss on heating), corrected for the corresponding water loss due to efflorescence, and by difference enabled calculation of the intial free moisture in the sample. This procedure, based on the mass balance principle of the thermal decomposition of sodium bicarbonate, was found to be accurate, reproducible and sensitive. It was capable of determining the moisture content in sodium bicarbonate samples at moisture levels as low as 0.01%. It was also capable of determining moisture content in sodium bicarbonate samples which are contaminated with sodium carbonate and sodium sesquicarbonate. Since the gravimetric procedure was undertaken in a vacuum oven, with the water and CO(,2) released being totally collected by absorption tubes in the vacuum outlet from the oven, no CO(,2) or water vapor pressure buildup occurred during an analysis. Accordingly the method had several advantages over the manometric procedures used by the previous investigators which enabled the new procedure to be successfully employed in kinetic studies to identify factors influencing the thermal decomposition of sodium bicarbonate. The decomposition kinetics of sodium bicarbonate were found to be best expressed geometrically with a model of a diminishing sphere rather than the more usual second order rate expression. The reaction was a surface controlled phenomenon, occurring in a crystalline solid. The results showed that the thermal stability of sodium bicarbonate differs with different sources of supply, and that the difference was related to the specific surface area of the sodium bicarbonate samples rather than the particle size. Due to the wide differences in internal surface area measured for the sodium bicarbonate samples, the specific surface area and the particle size were not always related. Although the stability of sodium bicarbonate differs with various suppliers, there was no significant correlation found between the stability of sodium bicarbonate and the stability of the effervescent systems containing these sodium bicarbonate samples. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI
Degree
Ph.D.
Subject Area
Pharmacology
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