Double membrane diaphragm technique for absolute measurements of diffusion coefficients

Abstract

A new technique for measuring diffusion coefficients utilizing two thin porous membranes separated by a spacer of known cross-sectional area and thickness is presented. The method permits absolute measurements of diffusion coefficients of chemical and biological materials in solution. The technique is based on the free-diffusion space between two membranes, thus avoiding the problems of solute-membrane interactions and tortuosity of the pore space that are present with single membrane diaphragms. Diffusion coefficient measurements of 5 × 10^–4 M NaCl and 5 × 10^–4 M KCl are in good agreement with values reported in the literature.