Electrokinetic studies on testosterone/aqueous electrolyte interface : Part 1. Electro-osmosis,electrophoresis, streaming potential and streaming current

The electrical properties of testosterone interfaces were investigated. For this purpose, measurements of electro-osmosis, hydrodynamic permeation, streaming potential and streaming currents of metabolically important solutions of the electrolytes NaCl, KCl and MgCl₂ (in the concentration range 10^?4?10^?3 mol/l) across a testosterone plug were carried out. Electrophoretic mobility of testosterone particles suspended in these electrolyte solutions was also studied. The data were analysed from the viewpoint of nonequilibrium thermodynamics. Phenomenological coefficients were evaluated from the linear transport equations and Saxen's relationship was verified. Dependence of phenomenological coefficients on electrolyte concentration was examined. Electro-osmotic and electrophoretic transport coefficients were found to vary linearly with concentration, whereas hydrodynamic permeation and membrane conductance coefficients show non-linear variation. The results are explained on the basis of structural modifications occurring during the passage of the permeating species through the membrane. The nature of the electrical double layer formed at the testosterone/solution interface was ascertained on the basis of the direction of electro-osmotic permeation and electrophoretic migration of testosterone particles.Zeta potentials were estimated in order to obtain a plausible picture of the electrical double layer at the testosterone/solution interfaces. Dependence of zeta potentials on concentration was examined and membrane parameters calculated. The double layer thickness was estimated, which reveals that the diffuse double layer is more compact in the case of MgCl₂ than in that of KCl.