DEVELOPMENT OF A BIENZYMIC GRAPHITE-TEFLON COMPOSITE ELECTRODE FOR THE DETERMINATION OF HYPOXANTHINE IN FISH

A bienzymic amperometric graphite-Teflon composite biosensor, in which xanthine oxidase and peroxidase, together with the mediator ferrocene , are incorporated into the electrode matrix, was developed for the de termination of hypoxanthine in fish samples, These biosensors were fab ricated by simple physical inclusion of the enzymes and the mediator i n the bulk of the graphite-Teflon matrix, A Teflon content of 60%, a w orking potential of 0.00 V, a temperature of 30 +/- 1 degrees C and a pH of 7.4 were selected as the optimum working conditions, The composi te bioelectrode operated over long periods owing to the renewability o f its surface by polishing, Reproducible amperometric responses were a chieved with different electrodes fabricated from different composite matrices, and no significant loss of the enzyme activity was observed after more than 6 months of storage at 4 degrees C, A detection limit for hypoxanthine of 9.0 x 10(-8) mol l(-1) was obtained by amperometry in stirred solutions, An interference study of different substances w hich may be present in samples together with hypoxanthine demonstrated very good selectivity for the determination of this analyte, The bien zymic composite biosensor was applied to the determination of hypoxant hine in sardine muscle tissue, and the method was validated by compari ng the results with those obtained by applying a recommended reference method.