Solvent-processible polymer membrane-based liquid junction-free reference electrode

A new type of liquid junction;free reference electrode system is devised by employing solvent-processible polymer membranes. The membranes are formulated with either a one-component silicone rubber or an aromatic-type polyurethane as the matrixes. The optimized formulations incorporate both cation- and anion-exchange sites (i.e,, potassium tetrakis(p-chlorophenyl)borate and tridodecylmethylammonium chloride) and; in the case of silicone rubber, a plasticizer. The silicone rubber-based membrane, while possessing minimal response toward most ions, is found to display a near-Nernstian response to pH change. The aromatic polyurethane matrix formulation, however; is not sensitive to pH over a wide range (i.e,, pH 2-12) and is shown to exhibit only a small emf variation (within +/-2 mV) toward a wide variety of salts added even at very high concentrations (i,e,, up to 0.1 M). Potentiometric emf responses of ISEs (e.g,, Na+, K+, Ca2+, Cl-), whether paired with a polymer membrane-based reference electrode or with a conventional liquid junction-type reference electrode, are shown to be remarkably similar within the precision of the measurement setup. The feasibility of adapting the proposed reference electrode to the planar solid-state sensor format is also demonstrated.