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A simple biosensor, constructed by bulk-modification of carbon ink with manganese dioxide as a mediator and glucose oxidase as a biocomponent was investigated for its ability to 2633 ORDER REPRINTS serve as amperometric detector for glucose in hydrodynamic as well as in flow injection analysis (FIA) mode. The sensor could be operated at a potential of 0.48 V under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited excellent reproducibility and stability. Factors influencing the amperometric response such as injection volume, flow rate and applied working potential were studied in detail. The screen-printed electrode exhibited a linear amperometric increase with the concentration of D-glucose from 2 to 2500 mg L À1 and gave a 3 detection limit of 0.085 mg L À1 . Due to its remarkable stability such a sensor could be operated continuously for more than four weeks or more than 1000 sample injections. No change of signal height could be observed within an operation period of 12 h. The sensor was exploited for FIA-amperometric determination of glucose in beer and wine samples.

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An amperometric method for the determination of the neurotoxic amino acid b-N-oxalyl-l-a,b-diaminopropionic acid (b-ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulkmodified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion-film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/ AgCl), flow rate 0.2 mL min , respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on-line use.