An oscillating electrical potential across a liquid membrane is studied as a model of a biological system. The oscillating potential is caused by repeated surfactant adsorption and desorption at the interface. The surfactant desorption process was simulated using both Fick's diffusion equation and the Langmuir-Hinshelwood equation. A water/octanol/water liquid membrane containing sodium dodecyl sulfate (SDS) was used and the effect of NaCl was studied. Calculations agree closely with experimental results, supporting the validity of the model we propose. Adsorption rate constants were obtained by comparing the experimental and calculated results. The addition of NaCl increased adsorption rate constants and decreased desorption rate constants. Calculations suggest that surfactant desorbs mainly into the octanol phase and this desorption is not affected by the addition of NaCl. The disordering of potential oscillations by NaCl addition may be caused by decreased SDS accumulation in the octanol phase close to the interface. A lower adsorption rate of the surfactant from the octanol phase onto the water/octanol interface leads to an oscillating electrical potential across the liquid membrane. (c) 2006 Elsevier B.V. All rights reserved.