A potentiometric reference electrode for use in an electrochemical analysis of an aqueous sample, comprising an electric conductor; an insulating layer on the conductor, the insulating layer having a throughgoing aperture defining an electrode region; and a heterogeneous membrane layer on the insulating layer in the electrode region for direct contact with the sample and for electrical contact with the conductor through the aperture, the heterogeneous membrane layer consisting of a plurality of hydrophobic and hydrophilic ion conducting electrolyte compartments which are intimately admixed; wherein the hydrophobic compartments of the heterogeneous membrane consist of a polymer selected from the group of poly-siloxanes, poly-organo-phosphazenes, poly-1 trimethyl-silyl-1-propyne, poly-4-methyl-2-pentyne and mixtures thereof; and characterized in that the hydrophilic Ion conducting electrolyte compartments of the heterogeneous membrane consist of at least one of a hydrophilic polymeric binder selected from polyvinyl alcohol, poly-hydroxymethacrylates, poly-acrylamides, poly-saccharides, cellulosic polymers and gelatins; a surfactant; an emulsifier; a pH buffer; cross-linkers and catalysts; at least one electrolyte salt; and a redox reagent for undergoing a potential determining reaction at the electrode. an electric conductor; an insulating layer on the conductor, the insulating layer having a throughgoing aperture defining an electrode region; and a heterogeneous membrane layer on the insulating layer in the electrode region for direct contact with the sample and for electrical contact with the conductor through the aperture, the heterogeneous membrane layer consisting of a plurality of hydrophobic and hydrophilic ion conducting electrolyte compartments which are intimately admixed; wherein the hydrophobic compartments of the heterogeneous membrane consist of a polymer selected from the group of poly-siloxanes, poly-organo-phosphazenes, poly-1 trimethyl-silyl-1-propyne, poly-4-methyl-2-pentyne and mixtures thereof; and characterized in that the hydrophilic Ion conducting electrolyte compartments of the heterogeneous membrane consist of at least one of a hydrophilic polymeric binder selected from polyvinyl alcohol, poly-hydroxymethacrylates, poly-acrylamides, poly-saccharides, cellulosic polymers and gelatins; a surfactant; an emulsifier; a pH buffer; cross-linkers and catalysts; at least one electrolyte salt; and a redox reagent for undergoing a potential determining reaction at the electrode. the hydrophobic compartments of the heterogeneous membrane consist of a polymer selected from the group of poly-siloxanes, poly-organo-phosphazenes, poly-1 trimethyl-silyl-1-propyne, poly-4-methyl-2-pentyne and mixtures thereof; and characterized in that the hydrophilic Ion conducting electrolyte compartments of the heterogeneous membrane consist of at least one of a hydrophilic polymeric binder selected from polyvinyl alcohol, poly-hydroxymethacrylates, poly-acrylamides, poly-saccharides, cellulosic polymers and gelatins; a surfactant; an emulsifier; a pH buffer; cross-linkers and catalysts; at least one electrolyte salt; and a redox reagent for undergoing a potential determining reaction at the electrode. at least one of a hydrophilic polymeric binder selected from polyvinyl alcohol, poly-hydroxymethacrylates, poly-acrylamides, poly-saccharides, cellulosic polymers and gelatins; a surfactant; an emulsifier; a pH buffer; cross-linkers and catalysts; at least one electrolyte salt; and a redox reagent for undergoing a potential determining reaction at the electrode.