Analysis of Urea Hydrolysis by Immobilized Urease in Urea‐Sensing Electrodes

摘要

AbstractUrea hydrolysis in an enzyme electrode that is sensitive to urea concentration has been analyzed with a theoretical model. The model incorporates nonlinear product‐inhibited, pH‐dependent kinetics, Nernst‐Planck diffusion, and ionic equilibria of product and buffer species. Simulation results indicate that film resistance can significantly reduce the detection range of the electrode and a Biot number (the ratio of characteristic internal to external mass transfer resistance) greater than 75 is necessary to minimize the film resistance. The electrode response depends on a balance between the reaction‐generated pH changes and the membrane diffusion resistances that sustain such pH shifts. The Damkohler number (the ratio of characteristic rate of reaction to that of diffusion) should be between one and five to maximize electrode sensitivity. The model has been used to demonstrate the effects of acetate, phosphate, and Tris buffers on electrode response. The carbonate concentration of dialysate solution is sufficient to shift the detection range of the electrode and reduce the sensitivity of the electrode by an order of magnitude. Tris buffer reduces the pH response of the electrode for buffer concentrations greater than 2 mM, because the pK of Tris falls within the range of the reaction‐generated