The determination of interfacial transfer constants using side-by-side diffusion cells

A side-by-side diffusion cell setup has been used to determine the pH 7.4 buffer-octanol interfacial transfer constants for twelve compounds. The compounds are a diverse selection of pharmaceuticals, amino acids, and small organics which covers a log distribution coefficient (K) range of -3 to 2. A model based on the resistance summation approach, which deals explicitly with the various barriers, involves in the transport process, was used to derive transfer constants from the transport data for each compound. The model gave constants that were well behaved in a published model describing the correlation of the forward and reverse transfer constants to equilibrium K values (r2 = 0.999). These studies demonstrate the utility of side-by-side diffusion cells for the determination of interfacial transfer constants. This type of setup offers the advantages of controlled interfacial area, measurable hydrodynamic effects, and a commercially available apparatus.