Transport of ions across the membranes was studied by use of porous glass (average pore radius of 20Å, corning #7930) modified with [3-(2-aminoethylamino)propyl]trimethoxysi-lane. Membrane potential was generated in the system with two aqueous solutions of different concentration of KCl, KNO3, or CH3COOK separated by the modified membrane. (Fig. 4) The membrane potential agree with the Theorell-Meyer-Sievers Theory. The fixed charge density of the modified porous glass membrane increased with the increase of the concentration of silane solution used in the modification reaction, while saturated at higher concentration than 0.01 mol·dm-3. This means a unit fixed charge occupies the area of 1500Å2 on the glass surface. This value is too large if compared with the least crosssectional area of one silane molecule. The addition of copper(II) ion in KCl solution decreased the membrane potential. It was presumed that copper(II) ion forms a complex with aminoethylamino groups on the modified porous glass surface, which might lower the fixed charge density of the modified membrane.
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