Amperometric sensor for hypoxanthine and xanthine based on the detection of uric acid

The construction and response of an immobilized enzyme modified electrode as an amperometric sensor is described. Xanthine oxidase was adsorbed on a carbon paste electrode and physically entrapped with a semipermeable membrane. Uric acid, the product of the enzymatic reaction, was oxidized electrochemically at +0.4 V vs. Ag/AgCl, yielding a steady-state current directly related to the bulk concentration of the substrate. Hypoxanthine and xanthine were determined in the range 5–100 μM at Ph 7.2 with good precision. Interferences are discussed.