Determination of oxalate in urine, using an amperometric biosensor with oxalate oxidase immobilized on the surface of a chromium hexacyanoferrate-modified graphite electrode. 2000

S Milardović, and Z Grabarić, and M Tkalcec, and V Rumenjak
University of Zagreb, Faculty of Chemical Engineering and Technology, Croatia.

A novel enzymatic amperometric method is described for the determination of oxalic acid in urine. An amperometric biosensor was made by immobilizing oxalate oxidase on the surface of a chromium(III) hexacyanoferrate-modified graphite electrode by using a bovine serum albumin and glutaraldehyde cross-linking procedure. The enzyme biocatalyzes oxalate decomposition in the presence of oxygen into carbon dioxide and hydrogen peroxide. The oxalate concentration, which is proportional to the amount of hydrogen peroxide, was determined amperometrically by measuring the current resulting in the reduction of hydrogen peroxide at a very low working potential (0.05 V versus the Hg ¿Hg2Cl2¿ 3M KCl electrode), which minimized the influence of the possible interferences present in human urine. All experiments were performed with succinic buffer, pH 3.8, containing 0.1M KCl and 5.4mM ethylenediaminetetraacetic acid. In an aqueous solution of pure oxalic acid, the biosensor showed good linearity in a concentration range of 2.5-100 microM without the use of a dialysis membrane. For untreated urine samples, a high correlation (R2 = 0.9949) was obtained between oxalate concentrations added to urine samples and oxalate recoveries calculated for determinations with the described oxalate biosensor.

UI MeSH Term Description Entries
D007202 Indicators and Reagents Substances used for the detection, identification, analysis, etc. of chemical, biological, or pathologic processes or conditions. Indicators are substances that change in physical appearance, e.g., color, at or approaching the endpoint of a chemical titration, e.g., on the passage between acidity and alkalinity. Reagents are substances used for the detection or determination of another substance by chemical or microscopical means, especially analysis. Types of reagents are precipitants, solvents, oxidizers, reducers, fluxes, and colorimetric reagents. (From Grant & Hackh's Chemical Dictionary, 5th ed, p301, p499) Indicator,Reagent,Reagents,Indicators,Reagents and Indicators
D010070 Oxalates Derivatives of OXALIC ACID. Included under this heading are a broad variety of acid forms, salts, esters, and amides that are derived from the ethanedioic acid structure. Oxalate,Ethanedioic Acids,Oxalic Acids,Acids, Ethanedioic,Acids, Oxalic
D010088 Oxidoreductases The class of all enzymes catalyzing oxidoreduction reactions. The substrate that is oxidized is regarded as a hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The recommended name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the acceptor. (Enzyme Nomenclature, 1992, p9) Dehydrogenases,Oxidases,Oxidoreductase,Reductases,Dehydrogenase,Oxidase,Reductase
D012015 Reference Standards A basis of value established for the measure of quantity, weight, extent or quality, e.g. weight standards, standard solutions, methods, techniques, and procedures used in diagnosis and therapy. Standard Preparations,Standards, Reference,Preparations, Standard,Standardization,Standards,Preparation, Standard,Reference Standard,Standard Preparation,Standard, Reference
D002021 Buffers A chemical system that functions to control the levels of specific ions in solution. When the level of hydrogen ion in solution is controlled the system is called a pH buffer. Buffer
D002138 Calibration Determination, by measurement or comparison with a standard, of the correct value of each scale reading on a meter or other measuring instrument; or determination of the settings of a control device that correspond to particular values of voltage, current, frequency or other output. Calibrations
D004563 Electrochemistry The study of chemical changes resulting from electrical action and electrical activity resulting from chemical changes. Electrochemistries
D004566 Electrodes Electric conductors through which electric currents enter or leave a medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum. Anode,Anode Materials,Cathode,Cathode Materials,Anode Material,Anodes,Cathode Material,Cathodes,Electrode,Material, Anode,Material, Cathode
D004800 Enzymes, Immobilized Enzymes which are immobilized on or in a variety of water-soluble or water-insoluble matrices with little or no loss of their catalytic activity. Since they can be reused continuously, immobilized enzymes have found wide application in the industrial, medical and research fields. Immobilized Enzymes,Enzyme, Immobilized,Immobilized Enzyme
D005295 Ferrocyanides Inorganic salts of the hypothetical acid ferrocyanic acid (H4Fe(CN)6).

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