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 . <EOS>