Novel amperometric biosensors sensitive to nitrate and nitrite were developed by combination of mediator-modified electrodes with immobilized nitrate reductase and nitrite reductase, respectively. The electron mediator of the electrode acts simultaneously as the electron donor of the enzyme. The quanitative determination of the substrates is based on the amperometric measurement of the cathodic current which results from the electron transfer of the enzymatic reduction of nitrate and nitrite, respectively. Electron mediators were characterized by determination of their redox reversibility, formal potentials, diffusion coefficients, and heterogeneous rate constants. Nitrate reductases from Aspergillus species, Escherichia coli, Paracoccus denitrificans, and Sulfurospirillum deleyianum as well as nitrite reductases from Paracoccus denitrificans and Sulfurospirillum deleyianum were used for the studies. The enzymes were immobilized by entrapment in a novel polycarbonyl sulfonate hydrogel. Using these enzymatic sensors for quantitative determination of nitrate and nitrite in aqueous solutions detection limits of 0,6 mg l"-"1 nitrate and 0,03 mg l"-"1 nitrite were obtained. Oxygen dependence of the measurement, low stability and high response time of the sensors are main problems which should be solved in future work. (orig.)SIGLEAvailable from TIB Hannover: RO 7603(14) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
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