A liquid electrolyte, for an electrochemical gas sensor for detecting NH3 or gas mixtures containing NH3, contains at least one solvent, one conductive salt and/or one organic mediator. The conductive salt is an ionic liquid, an inorganic salt, an organic salt or a mixture thereof. The electrolyte preferably is comprised of (I) water, propylene carbonate, ethylene carbonate or a mixture thereof as solvent; (ii) LiCl, KCl, tetrabutylammonium toluenesulphonate or 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate as conductive salt; and (iii) tert-butylhydroquinone or anthraquinone-2-sulphonate as organic mediator.