Analytical Sciences

Calculation of Concentration and Electrostatic PotentialProfiles at Liquid-Membrane/Water and Liquid/Liquid Interfaces

A. VINCZE*, G. HORVAI* * and F. A. M. LEERMAKERS**

*Technical University, Budapest, Hungary
**Wageningen Agricultural University, The Netherlands

A method based on statistical thermodynamics has been used to describeconcentration distributions of neutral andcharged molecules in the vicinity of liquid-liquid or polymermembrane-liquid interfaces. The model is outlined andvarious applications are shown. One of these is a study of the transitionregion at the interface of two immiscible liquids.The results show that this transition is not sharp. The width of theinterfacial region (where the concentration variesgradually) depends on the mutual solubility of the two liquids and on thesize of the molecules. In another application thepotential drop across the interfacial region has been calculated as afunction of composition of the bulk phases. This typeof calculation allowed the numerical simulation of the potentiometricbehavior of a recently developed ion-selectiveelectrode which employs negatively charged ion carrier. (Keywords: Statistical thermodynamics, concentration distribution,charged molecule, interface, immiscible liquids)

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