Abstract: An ion sensitive electrode device which consists of one or more ion-pairs distributed in at least one of two or more immiscible phases consisting of an aqueous phase, an organic phase, a polymer phase or a solid electrolyte phase. A reference solution includes an aqueous solution of the ion-pair and a high concentration of a micelle former such as an anionic or cationic detergent or a ligand. The device can be used to measure organic and inorganic compounds or can be readily modified by the addition of a biological material to the reference solution for the bioassay for bioorganic compounds.