SOLVENT-PROCESSIBLE POLYMER MEMBRANE-BASED LIQUID JUNCTION-FREE REFERENCE ELECTRODE

A new type of liquid junction;free reference electrode system is devis ed by employing solvent-processible polymer membranes. The membranes a re formulated with either a one-component silicone rubber or an aromat ic-type polyurethane as the matrixes. The optimized formulations incor porate 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 polyu rethane matrix formulation, however; is not sensitive to pH over a wid e range (i.e,, pH 2-12) and is shown to exhibit only a small emf varia tion (within +/-2 mV) toward a wide variety of salts added even at ver y high concentrations (i,e,, up to 0.1 M). Potentiometric emf response s of ISEs (e.g,, Na+, K+, Ca2+, Cl-), whether paired with a polymer me mbrane-based reference electrode or with a conventional liquid junctio n-type reference electrode, are shown to be remarkably similar within the precision of the measurement setup. The feasibility of adapting th e proposed reference electrode to the planar solid-state sensor format is also demonstrated.