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 (Meldola Blue), dissolved in the carrier solution in a flow-injection system, was found to reduce the oxidation potential for hydrogen peroxide from 600-1200 mV without mediator to - 100 mV vs, Ag/AgCl with the mediator present. The very low background current of reticulated vitreous carbon (RVC) at this potential makes it possible to detect very low levels of hydrogen peroxide or glucose. Glucose oxidase was covalently coupled with carbodiimide to RVC, and the RVC was formed into a column inserted in a flow-injection system. The calibration curve was linear from 30 nM to 10 mu M glucose with 5 mu M mediator. At higher mediator concentrations, the linear range was extended to 1000 mu M, but with a much higher background current. The sample throughput was about 60 h(-1). The current response decreased to 50% of the original response 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 rate of 1 mi min(-1) at mediator concentrations of 5 and 50 mu M respectively.