Experimental data have been obtained using an Analytical Ultracentrifuge, in regions much closer to the interface in immiscible liquid/liquid systems than have hitherto been reported. The water/toluene system was investigated with acetic and propionic acids as the transfer solutes. The direction of mass transfer was from the water to the toluene phase. The data derived from the study indicates that the maximum mass transfer flux in the water/toluene system occurs, not at the interface, but at regions further away from it and that the water/toluene system offers significant interfacial resistance of about 104 s/cm to the transfer of acetic and propionic acids. The water/n-butanol system was also studied and found to offer negligible resistance to the transfer of acetic acid across the interface.

Diffusion coefficients for ethylene glycol, glycerol, and n-butanol in water were also determined with the Ultracentrifuge. The values derived in this study were reproducible to within 5% and were in close agreement with those derived from classical diffusion experiments.