A methylviologen-doped zeolite modified carbon paste electrode was applied to the amperometric detection of alkali metal cations in ion chromatography. The detection principle is based on the ion exchange of methylviologen by the target cationic analyte, followed by the reduction of methylviologen at the electrode surface at an operating potential of −0.85 V (vs. SCE). When using a solution of tetrabutylammonium bromide as the mobile phase, the background response was very low because of the size exclusion of tetrabutylammonium ions from the zeolite framework, and the modified electrode was only sensitive to non size-excluded cations. In a large volume wall-jet cell configuration, the sensor allowed the analysis of non reducible non size-excluded cations after their separation on an ion exchange column, in both the presence and the absence of dissolved oxygen. Use of a mobile phase with cations too large to be detected by the zeolite modified electrode did not require any further suppressor technique.