A COMPARISON OF DIFFUSION COEFFICIENTS STUDIED THROUGH NATURAL AND SYNTHETIC MEMBRANES (SILVER, CELLULOSE ESTERS, POLYCARBONATE)
Abstract
An investigation was undertaken to study the measurement of diffusion coefficients of several pharmaceutically significant compounds through natural and synthetic membranes. The four synthetic membranes were composed of silver metal, inert esters of cellulose, a cellulosic membrane strengthened with nylon interweb or a polycarbonate film containing uniformly distributed pores. The latter two membranes were found suitable for the diffusion method developed during this study. The compounds, selected for their relevance to topical formulations, were benzoic acid, an homologous series of the parabens, hexachlorophene and benzalkonium chloride. An experimental system was designed for the continuous measurement of the concentrations of the selected chemicals after their penetration through the test membrane. Diffusion coefficients were evaluated at the normal biological temperature of 37.5(DEGREES)C and values from the automated system were related to those from a standard static method. The validity of the results from the automated system was also shown by ascertaining the diffusion coefficient of benzoic acid at 30(DEGREES)C, a temperature at which this constant had previously been determined. One experimental method of analysis incorporated the use of an ion-selective electrode to measure the activity of potassium ion transferred through the membrane. The diffusion of a salt of known diffusion coefficient was necessary to determine the cell constant. Diffusion coefficients of several aromatic chemicals were analyzed by an automated system which continuously monitored by a suitable spectrophotometer the concentration of the penetrant as a function of time. Chloroform:water and peanut oil:water equilibrium partition coefficients were evaluated at 37.5(DEGREES)C. An interpretation of permeability measurements provided an insight into the structure of the membranes. Because of their similar solubility properties in an aqueous environment, the results for benzoic acid and the three parabens were grouped together for comparison. Diffusion coefficients were plotted as a function of chloroform:water and oil:water partition coefficients. These partition coefficients were also related to the product of diffusion coefficients and the square root of the molecular weight. A linear relationship was found between the diffusion coefficient and the inverse square root of the molecular weight of the diffusing substance. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI
Degree
Ph.D.
Subject Area
Organic chemistry
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