UREA BIOSENSORS BASED ON PVC MEMBRANE ION-SELECTIVE ELECTRODES

This paper presents a general method of enzyme immobilization at the s urface of ion selective membranes. Covalent binding of enzymes directl y on the electrode surface is a very effective method that results in stable enzymatic membranes. As an example the construction of enzymati c sensors for urea determination based on ammonium and hydrogen carbon ate ion selective electrodes is presented. The optimum working conditi ons for these biosensors were found. Bioelectrodes based on an ammoniu m sensor show very good analytical parameters: dynamic stability - ove r 2 months without decrease of sensitivity, response time - shorter th en 20 s, high sensitivity, determination range from 0.3 to 70 mM. In t he contrast to the ammonium ion based biosensors, those constructed on the basis of anion selective electrodes have worse analytical paramet ers. It is mainly due to poor selectivity and instability of an applie d ion selective electrode. In spite of this, both types of urea biosen sors were used for measurements in the differential potentiometry mode . The application of such system increased the sensitivity of urea det ermination.