Interfacial Barriers in Interphase Transport: Retardation of the Transport of Diethylphthalate Across the Hexadecane-Water Interface by an Adsorbed Gelatin Film

Abstract

In order to investigate the possible influence of an adsorbing substance upon the oil-water interphase transport rate of a solute, experiments were conducted on the rate of release of diethylphthalate from hexadecane droplets dispersed in an aqueous sodium sulfate solution. It was found that when an adsorbed layer of gelatin is presented, the rates of solute release are the order of 1 × 104 times slower than diffusion controlled. The permeability coefficient for the interfacial barrier was estimated to be 1.5 × 10−5 ± 0.3. These findings are, to the authors' knowledge, the first of their kind, and suggest the possible importance of such nonspecific barriers in biopharmaceutics. The data have been critically analyzed by several physical models that relate the interphase transport rate to the partition coefficient, the diffusion coefficient in the aqueous phase, the particle-size distribution of the droplets, the interfacial resistance of the gelatin layer, and the adsorption of the solute to the interface. The analysis has shown that under certain conditions adsorption of diethylphthalate at the interface must be accounted for to provide quantitative agreement of the theory with the data.