FLOW-INJECTION DETERMINATION OF TRACE HYDROGEN-PEROXIDE OR GLUCOSE UTILIZING AN AMPEROMETRIC BIOSENSOR BASED ON GLUCOSE-OXIDASE BOUND TO A RETICULATED VITREOUS CARBON ELECTRODE

An electron transfer mediator, 8-dimethylamino-2,3-benzophenoxazine (M eldola Blue), dissolved in the carrier solution in a flow-injection sy stem, was found to reduce the oxidation potential for hydrogen peroxid e from 600-1200 mV without mediator to - 100 mV vs, Ag/AgCl with the m ediator present. The very low background current of reticulated vitreo us carbon (RVC) at this potential makes it possible to detect very low levels of hydrogen peroxide or glucose. Glucose oxidase was covalentl y coupled with carbodiimide to RVC, and the RVC was formed into a colu mn inserted in a flow-injection system. The calibration curve was line ar from 30 nM to 10 mu M glucose with 5 mu M mediator. At higher media tor concentrations, the linear range was extended to 1000 mu M, but wi th a much higher background current. The sample throughput was about 6 0 h(-1). The current response decreased to 50% of the original respons e after 20 days. The coulometric yield was high because the sample was pumped through the pores of the RVC. It was 16% and 55% at a flow rat e of 1 mi min(-1) at mediator concentrations of 5 and 50 mu M respecti vely.