MEDIATED AMPEROMETRIC BIOSENSOR FOR HYPOXANTHINE BASED ON A HYDROXYMETHYLFERROCENE-MODIFIED CARBON PASTE ELECTRODE

An amperometric enzyme electrode for the determination of hypoxanthine in fish meat is described. The hypoxanthine sensor was prepared from xanthine oxidase immobilized by covalent binding to cellulose triacetate and a carbon paste electrode containing hydroxymethylferrocene. The xanthine oxidase membrane was retained behind a dialysis membrane at a carbon paste electrode. The sensor showed a current response to hypoxanthine due to the bioelectrocatalytic oxidation of hypoxanthine, in which hydroxymethylferrocene served as an electron-transfer mediator. The limit of detection is 6 x 10(-7) M, the relative standard deviation is 2.8% (n = 28) and the response is linear up to 7 x 10(-4) M. The sensor responded rapidly to a low hypoxanthine concentration (7 x 10(-4) M), the steady-state current response being achieved in less than 1 min, and was stable for more than 30 days at 5-degrees-C. Results for tuna samples showed good agreement with the value determined by the conventional method.