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Sodium-selective coated wire electrodes (CWE) and solid contact (SC) electrodes have been constructed and Investigated. The CWE Is based on the application of a poly(vinyl chloride) (PVC) membrane Incorporating the sodium-selective Ionophore tetraethyl ester of p-/erf-butylcallx[4]arene onto the surface of a platinum disk. The SC electrode Is based on the use of a conducting polymer, polypyrrole (PPy), doped with NaBF« as the mediating layer between platinum and the same PVC membrane as above. Nernstlan responses have been obtained for both electrodes and comparable selectlvlties to that of a conventional lon-selectlve electrode (ISE) based on the same Ionophore. Impedance measurements of the PPy and PVC layers and potentlometrlc studies of the membranes have been used to Investigate the mechanism of the charge transfer of the systems.