Amperometric Determination of Ammonium and Urea with Enzyme Based Probes

Abstract

This chapter describes amperometric determination of ammonium and urea with enzyme-based probes. Amperometric enzyme probes for ammonium and urea have been assembled, and evaluated using immobilized glutamate dehydrogenase, and urease enzymes coupled with a platinum electrode. Analytical parameters such as pH, buffer, temperature, probe life-time, enzyme immobilization, cofactor concentration, and response time have been optimized. In reaction, 2 NH4+ competes with the Pt electrode for NADH in the presence of the enzyme glutamate dehydrogenase, and α-ketoglutarate, so the current signal due to the oxidation of NADH will decrease in the presence of NH4+. This decrease is proportional to the concentration of NH4+ in the sample. It is found that since NH4+ is the product of urea hydrolysis catalyzed by urease, in presence of both the enzymes urease, and glutamate dehydrogenase, urea also can be analyzed. Better reproducibility and stability was achieved using the enzyme GLDH type III, and NADH at a concentration of 10-3 mol/L urea has been, determined in the range 2×105–5×104 mol/L using the enzyme urease in solution first, and then immobilized on nylon net.