ENZYME BIOSENSORS FOR UREA DETERMINATION BASED ON AN IONOPHORE FREE PH MEMBRANE-ELECTRODE

A new type of enzymatic sensors for the determination of urea based on an ionophore-free pH membrane electrode has been constructed. The mem brane material was polyvinyl chloride modified with 1,4-diaminobutane. Chemical urease immobilization enabled the formation of a mono- and b imolecular enzyme layer directly on the pH sensor surface. The influen ce of the immobilization method modifications on the biosensor propert ies was investigated. The most important features of the obtained sens ors were high sensitivity, long lifetime (over 1 month) and short resp onse time (2-5 min for steady state). The characteristics of the senso rs were examined at different buffer concentrations, pH values and sti rring rates. The results obtained were in good agreement with theoreti cal predictions. optimal measurement conditions were evaluated (a buff er concentration of 5 mM and pH 6) for the urea concentration working range from 0.1 to 30 mM.