STUDIES ON IMMOBILIZATION SCHEMES FOR UREA ELECTRODES BASED ON AMMONIUM ION-SELECTIVE ELECTRODES

Studies on urea electrodes based on various styles of immobilizing the enzyme in membranes used in association with a nonactin based poly(vi nyl chloride) PVC matrix membrane ammonium ion-selective electrode are described. Approaches involving physical entrapment in polyacrylamide -methacrylamide and in PVC, adsorption on to Biodyne transfer membrane and to Immunodyne immunoaffinity membrane, covalent linking to bovine serum albumin, and covalent linkage with or without lysine spacer to nylon fabric were studied. The best electrode lifetimes and best gener al qualities were obtained for the system based on immobilization of u rease to nylon fabric, but without recourse to lysine spacer. The urea electrode calibration slopes were generally in the region of 50 mV de cade(-1) of urea concentration. Attempts to obtain urea electrodes by a spin-coating procedure of immobilizing urease on polyamide, or alter natively by immobilizing the enzyme directly on to a copolymer of viny l alcohol-vinyl chloride admired with PVC in the sensing membrane of t he ammonium ISE failed to yield any worthwhile responses.