Ion Transport Across a Bilayer Lipid Membrane in the Presence of Dilute Tetraphenylborate

Cathodic and anodic current waves symmetrical about the point (0 V, 0 A) were recorded in cyclic voltammograms for the ion transport across a bilayer lipid membrane (BLM) between two aqueous phases (W1 and W2) containing 4 × 10 −7 –10 −5 mol dm −3 (M) tetraphenylborate (TPhB − ) and 0.1 M NaCl. The relationship between the membrane potential and the steady‐state current was recorded by normal pulse voltammetry. It is proved that the relationship symmetrical about the origin point (0 V, 0 A) mainly results from not only the transport of TPhB − but also that of Na + between W1 and W2 across the BLM. When the concentration of TPhB − in W1 and W2 was higher than 4 × 10 −6 M, their current‐potential curves were sigmoidal. Because TPhB − served as a carrier of Na + under the steady‐state condition, the current was caused by the antiport of TPhB − and Na + . On the other hand, the maximum point of the steady‐state current in their relationships was observed in the case that the concentration of TPhB − was lower than 1 × 10 −6 M. The reason that the maximum point appears has been clarified yet until now. The decline in the steady‐state current in the potential region higher than 0.1 V could be caused by the decrease in total ion concentration within the BLM owing to the outflow of TPhB − in connection with the inflow of Cl − . This indicates that the transport ion species and their proportion vary with the applied membrane potential.