KINETIC-MODEL OF PH-BASED POTENTIOMETRIC ENZYMATIC SENSORS .4. ENZYMELOADING 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 a nd concentration of buffer or concentration of analyte. It allows a qu antitative description of enzyme activity in the sensing membrane, and so is helpful incomparisons of various biosensors working under diffe rent conditions. The lifetime factor is defined in terms of the depend ence of the enzyme loading factor with time. Both factors are universa l parameters for pH-based enzymic sensors. The utility of these factor s in a description of biosensors is exemplified with pH-membrane elect rodes sensitized for urea using different methods of enzyme immobiliza tion.