Thin-layer CVs of oNPOE/PVC membranes doped with 5 mM ionophore 1, L, in the presence of (A) 5 mM sodium acetate and 5 mM barium acetate, (B) 5 mM barium acetate, (C) 5 mM sodium acetate and 5 mM strontium acetate, or (D) 5 mM strontium acetate. Potentials are defined against the average peak potential of Na+ transfer. Potential sweep rate, 0.05 V/s.