Enzyme electrodes ascorbic acid

Another approach to improve selectivity is to use an enzyme electrode. The enzyme ascorbate oxidase has been used successfully to remove ascorbate as an interference of in vivo voltammetric electrodes 219,320) Ascorbate oxidase converts the ascorbic acid to dehydroascorbate which is not electroactive in the potential region used for in vivo analysis. 

Biosensors fabricated on the Nafion and polyion-modified palladium strips are reported by C.-J. Yuan [193], They found that Nafion membrane is capable of eliminating the electrochemical interferences of oxidative species (ascorbic acid and uric acid) on the enzyme electrode. Furthermore, it can restricting the oxidized anionic interferent to adhere on its surface, thereby the fouling of the electrode was avoided. Notably, the stability of the proposed PVA-SbQ/GOD planar electrode is superior to the most commercially available membrane-covered electrodes which have a use life of about ten days only. Compared to the conventional three-dimensional electrodes the proposed planar electrode exhibits a similar... 

How analytical methods deal with interferences is one of the more ad hoc aspects of method validation. There is a variety of approaches to studying interference, from adding arbitrary amounts of a single interferent in the absence of the analyte to establish the response of the instrument to that species, to multivariate methods in which several interferents are added in a statistical protocol to reveal both main and interaction effects. The first question that needs to be answered is to what extent interferences are expected and how likely they are to affect the measurement. In testing blood for glucose by an enzyme electrode, other electroactive species that may be present are ascorbic acid (vitamin C), uric acid, and paracetamol (if this drug has been taken). However, electroactive metals (e.g., copper and silver) are unlikely to be present in blood in great quantities. Potentiometric membrane electrode sensors (ion selective electrodes), of which the pH electrode is the... 

Lowry JP, O Neill RD. Homogeneous mechanism of ascorbic acid interference in hydrogen peroxide detection at enzyme-modified electrodes. Analytical Chemistry 1992, 64, 453 156. 

Acetylcholineesterase and choline oxidase Carbon-fiber micro-electrode for determination of ACh and choline, mounted in a glass capillary tube. Enzyme was immobilized on the surface of the carbon fiber with albumin. Electrode was dip-coated with Nafion. Evaluation of selectivity and dynamic range, at a fixed potential of 1.2 V versus Ag-AgCl. Calibration graph for ACh and Ch was rectilinear between 0.1 and 3mM. Interference from ascorbic acid was not observed in the range 0.1 to 0.3 mM. [79]... 

Electrodes based on the immobilization of enzymes at the electrode surface have been reported for a few pharmaceutical applications. Seegopaul and Rechnitz developed a CO2 electrode that responds to methotrexate due to the inhibition of dihydrofolate reductase by the analyte. Additional applications have included the detection of penicillin consumption by penicillinase as well as urea by urease with a pH electrode and analysis of L-ascorbic acid by ascorbate oxidase.f ... 

Akyilmaz, E. Dinckaya, E. A new enzyme electrode based on ascorbate oxidase immobilized in gelatin for specific determination of L-ascorbic acid. Talanta 1999, 50, 87-93. 

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