US Patent 7658826 Reference electrode

A reference electrode including a water-impermeable, non-conductive substrate having a surface; an electrically conductive metal/metal salt mixture layer in contact with the surface; a water-soluble alkali metal salt layer; and a water-impermeable barrier layer overlaying a portion of the alkali metal salt layer and a portion of the metal/metal salt layer, and a method for preparing same are described. When the reference electrode is placed in a water sample to be tested, water enters the exposed portion of the alkali metal salt layer where it dissolves the salt forming a saturated solution in the region of contact between the alkali metal salt layer and the metal/metal salt layer.