Graphite-teflon composite bienzyme electrodes for the determination of cholesterol in reversed micelles. Application to food samples

A bienzyme amperometric composite biosensor for the determination of free a nd total cholesterol in food samples is reported. Cholesterol oxidase and h orseradish peroxidase, together with potassium ferrocyanide as a mediator, are incorporated into a graphite-70% Tenon matrix. The compatibility of thi s biosensor design with predominantly nonaqueous media allows the two of re versed micelles as working medium. The reversed micelles are formed with et hyl acetate as continuous phase tin which cholesterol is soluble), a 4% fin al concentration of 0.05 mol L-1 phosphate buffer solution, DH 7.4, as disp ersed phase, and 0.1 mol L-1 AOT as emulsifying agent. Studies on ;the repe atability of the amperometric response obtained at +0.10 V, with and withou t regeneration of the electrode surface by polishing, on the useful lifetim e of one single biosensor and on the reproducibility in the fabrication of different pellets illustrate the robustness of the biosensor design. Determ ination of free and total cholesterol in food samples such as butter, lard, and egg yoke was carried out, and the obtained results were advantageously compared with those provided by using a commercial Boehringer test kit.