Coulometric titration of D(+)-glucose using its enzymatic oxidation

A definitive method is described for the indirect assay of milligram quantities of D(+)-glucose by coulometric titration. D(+)-Glucose was aerobically oxidized by glucose oxidase in an acetate buffer solution (pH 5.1). Subsequently, the enzymatically formed hydrogen peroxide was titrated coulometrically with electrogenerated hypobromite in sodium bromide-sodium tetraborate medium of pH 8.6, with biamperometric end-point detection. Parameters affecting the enzymatically catalyzed oxidation and coulometric titration were evaluated. The optimized conditions for the oxidation of up to 20 mg of D(+)-glucose include the addition of 4500 U of glucose oxidase and stirring over a 10-min interval at 25 degrees C. Under proposed conditions, the assay values of several commercial D(+)-glucose reagents were somewhat lower than the guaranteed minimum values, with RSDs (n = 5) of 0.071 - 0.106%.