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Polypyrrole membrane was coated on a carbon felt surface by electropolymerization of pyrrole in an undiluted cucumber juice solution which contains a large amount of ascorbate oxidase. It was found that the polymerized carbon felt exhibited a large ascorbate oxidase activity. An ascorbate sensor, combining an oxygen electrode and the treated carbon felt membrane, was prepared by placing this carbon felt on the oxygen gas permeable membrane of an oxygen electrode. The resulting sensor gave a large current response of L-ascorbic acid, which is based on the consumption of oxygen catalyzed by ascorbate oxidase immobilized into the polypyrrole membrane. The optimum polymerization potential was found to be + 0.7 V (vs. SCE). The linear concentration range of L-ascorbic acid ranged from 5 x M. The enzyme immobilized into the polypyrrole membrane activity retained its activity for 5 days, and the half-life of the immobilized enzyme was about 10 days at 4°C.to 4 x

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