Gluconic acid, enzymatic oxidation

A second principle used widely for glucose analysis, is that of the oxidation of glucose enzymatically, mediated by the action of glucose oxidase with the formation of gluconic acid and hydrogen peroxide (22). In this procedure it is the hydrogen peroxide which is usually assayed for determination of glucose. This method suffers from the action of inhibitors which occur, particularly with patients in a diabetic coma and these need to be removed. 

Lactobionic acid. This derivative is produced by oxidation of the free carbonyl group of lactose (Figure 2.25), chemically (Pt, Pd or Bi), electro-lytically, enzymatically or by fermentation. Its lactone crystallizes readily. Lactobionic acid has found only limited application its lactone could be used as an acidogen but it is probably not cost-competitive with gluconic acid-<5-lactone. It is used in preservation solutions for organs prior to transplants. 

As for hydrogenation, heterogeneous catalytic oxidation of carbohydrates was essentially performed in the presence of carbon-supported metal catalysts, namely Pt, Pd or Bi-doped Pd.[57] Oxidation of glucose into gluconic acid, the worldwide production of which is around 60000 tons year 1,[52] is used in the food and pharmaceutical industry, and is produced today by enzymatic oxidation of D-glucose with a selectivity in gluconic acid close to 100%. 

In this test, oxygen from air is used for the enzymatic oxidation of (3-D-glucose in the presence of immobilized GOD to gluconic acid and hydrogen peroxide. Hydrogen peroxide can be determined by a second enzyme reaction. With horse radish peroxidase as catalyst o-phenylendiamine is oxidized by H2O2 to 2,3-diaminophenazine, which can be photometrically determined at 490 nm, thus establishing a quantitative relationship between active GOD sites and the intensity of the absorption band. 

As the solution passes through the column, the glucose is enzymatically oxidized to 8-D-gluconolactone (which is hydrolyzed to gluconic acid nonenzymatically) with utilization of O2. Change in O2 concentration, related to the amount of glucose in solution, is determined with 02-sensitive electrodes placed at the top and bottom of the column. The column may be used repeatedly. 

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