KINETIC-MODEL OF PH-BASED POTENTIOMETRIC ENZYMATIC SENSORS .4. ENZYME LOADING AND LIFETIME FACTORS

Two factors: enzyme loading factor and lifetime factor, are defined on the basis of a kinetic model for pH-based enzymic sensors. The enzyme loading factor is independent of measurement conditions, such as pH and concentration of buffer or concentration of analyte. It allows a quantitative description of enzyme activity in the sensing membrane, and so is helpful incomparisons of various biosensors working under different conditions. The lifetime factor is defined in terms of the dependence of the enzyme loading factor with time. Both factors are universal parameters for pH-based enzymic sensors. The utility of these factors in a description of biosensors is exemplified with pH-membrane electrodes sensitized for urea using different methods of enzyme immobilization.