Effect of Ion Species and Their Concentration on the Iontophoretic Transport of Benzoic Acid through Poly(vinyl acetate) Membrane

Effects of ion species and their concentration on the iontophoretic transport of benzoic acid through an artificial membrane [poly(vinyl acetate)] were investigated using a 2-chamber diffusion cell equipped with platinum electorodes and a constant current power source. The cathode side of the cell was filled with sodium benzoate solution, and the anode side with pottassium chloride, lithium chloride or teraethylammonium bromide solution. When the molar concentration of sodium benzoate in the cathode side (0.21 M) was the same as the potassium chloride in the anode side, the amounts of benzoate anion and potassium cation permeated through the membrane were greater with increasing current. With an increase in the concentration of benzoate anion in the cathode side and a constant concentration of potassium cation in the anode side, the amount of the former that permeated was proportional to the concentration applied, while permeation of potassium cation remained almost constant at a constant current of 0.2mA. Conversely, an increase in the concentration of potassium cation in the anode side with a constant concentration of benzoate anion in the cathode side resulted in an increase of the permeation of potassium cation and a decrease of that of benzoate anion, respectively, at the same constant current. When potassium chloride in the anode side was replaced by tetraethylammonium bromide, the amount of benzoate anion permeated was increased at a constant current of 0.2mA. These results may be explained by the following theory on the transport number of each ion through the artificial membrane : Current density calculated from ion flux throutgh the membrane was almost the same as that measured by observed current density. The results appeared to indicate that not only an ion species and its concentration in the donor solution but also ion species in the receiver solution should be considered when evaluating the iontophoretic transport phenomena.