A capillary-tube method for the measurement of solute transport across liquid-liquid interfaces

Solute transfer kinetics across aqueous-solution/organic-liquid interfaces have been measured by a method based upon the capillary-tube procedure for self-diffusion. A short capillary containing radiolabeled solute dissolved in one phase is immersed in a large stirred volume of the second liquid phase, into which the movement of marker is followed. Demonstration and validation of the approach have been performed with a number of systems of various configurations including the transport of salicylic and acetic acids across water/isopropyl myristate and water/dodecane interfaces. The results are in good general agreement with data obtained by the rotating diffusion cell technique. The temperature dependence of the kinetics determined with the capillary tube procedure shows Arrhenius behavior and should permit, therefore, thermodynamic parameters associated with interfacial transport to be evaluated.