An amperometric biosensor based on carbon paste electrodes (CPEs) for the determination of urea was constructed by enzyme (urease/GL-DH)-modified method. Urea was hydrolyzed to NH 4 + by catalyzing urease onto the enzyme-modified electrode surface in sample solution. In the presence of α-ketoglutarate and reduced nicotinamide adenine dinucleotide(NADH), a liberated NH 4 + produce to L-glutamate and NAD + by Lglutamate dehydrogenase (GL-DH). After the chemical reaction was proceeded, the

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... hemical reaction was occurred that an excess of the NADH was oxidized to NAD + . The oxidation current of NADH was monitored at +1.10 volt vs. Ag/AgCl. An optimum conditions of biosensor were investigated: The optimum pH range for catalyzed hydrolysis reaction of urea was pH 7.0-7.4. The linear response range and detection limit were 2.0 × 10 −5~2 .0 × 10 −4 M and 5.0 × 10 −6 M, respectively. Another physiological species did not interfere, except L-ascorbic acid.