A GRAPHITE PASTE ELECTRODE CONTAINING PEROXIDASE AND ITS APPLICATION

A mediator-less enzyme electrode for the detection of hydrogen peroxid e was made up by packing {one end of a glass tube (5 mm diam.)} with a graphite paste composed of 0.3 g of graphite powder, 0. 18 ml of liqu id paraffin, 6 mg of horse radish peroxidase (HRP) and 45 mul of gluta raldehyde (20 % solution). This electrode responded to hydrogen peroxi de at 0 V (vs. Ag/AgCl) in the absence of a mediator such as hexacyano ferrate(II). The current response was found to be based on a direct el ectron transfer between the bound cofactor (ferriprotoporphyrin IX) in the immobilized HRP molecule and graphite particle. A logarithmic plo t of the current response vs. the hydrogen peroxide concentration gave a straight line with a slope of 0.84 over the range of 2 X 10(-6) app roximately 2 X 10(-4) M. Similarly, enzyme electrodes for glucose and uric acid were prepared by co-immobilizing HRP in the paste along with glucose oxidase and uricase, respectively, both of which were hydroge n peroxide-producing oxidases. Each of these electrodes responded to g lucose or uric acid at 0 V. The current response was linearly related to the glucose or uric acid concentration, in the range of 2 X 10(-6) approximately 2 X 10(-3) M or 1 X 10(-5) approximately 2 X 10(-3) M.