MINIMIZATION OF ASYMMETRY POTENTIAL IN ETH 129-BASED CALCIUM-SELECTIVE MEMBRANE ELECTRODES

PVC-based calcium-selective electrodes doped with ETH 129 usually suffer from a shift in the standard potential when they are in contact with protein-containing solutions (e.g, blood serum) after being calibrated with aqueous standards. The shift is due to the development of asymmetry potential in inherently symmetric PVC membranes through the contamination of outer membrane surface by proteins in the biological samples. Membranes prepared with polyurethane showed much reduced shifts in terms of standard potential. This study was performed with a flow-injection system following a protocol designed to observe minor shifts in baseline potential. Other electrochemical properties of the system, including selectivity and response slope, were similar to those obtained with regular PVC-based ones. PVC-based calcium selective membrane electrodes, doped with commonly used ETH 1001, were also tested to compare their electrochemical performances.