INFLUENCE OF UNSTIRRED LAYERS ON THE DETE RMINATION OF DIFFUSION PARAMETERS

The use of membranes in release processes and diffusion experiments re quires the knowledge of the membrane specifications, particularly the permeability. For the determination of diffusion parameters the effect of the thin area close to the membrane with no real convection should be considered. The so called ''unstirred layers'' may cause a remarka ble effect on diffusion parameters. The permeability of these layers d epends on stirring conditions, diffusion cell geometry, viscosity of t he medium and temperature. The use of a relatively simple diffusion ce ll for the determination of diffusion parameters is described. Further more, the different means to investigate the effect of the unstirred l ayers and a new evaluation method is explained. The use of this proced ure is shown for water and paraffin as liquid media.