Abstract: The polypyrrole films were prepared as previously described (Ibid, 1990, 1, 537) then glucose oxidase was covalently immobilized onto the electrode by immersing the electrode into a solution of the enzyme with activated carboxylic side chains and in the presence of glucose to block the active sites. After rinsing with 1 M KCl, the immobilized enzyme was crosslinked with 2% glutardialdehyde for 10 min to improve stability. The glucose oxidase electrode and the non-enzyme electrode were mounted in the flow-through cell of a flow injection system (described) and a potential of 600 mV vs. SCE was applied. The apparatus was applied to the determination of glucose in the presence of co-oxidizable compounds in fruit juice and wines. Due to the size-exclusion properties of polypyrrole, the thicknesses of the conducting polymer layers at both electrodes had to be equal to allow interfering compounds to be discriminated. Polypyrrole - glucose oxidase electrodes with the enzyme covalently bound to the outer surface of the functionalized polymetric network (prep. described) are used together with a similarly prepared non-enzyme electrode to determine glucose in the presence of co-oxidizable compounds in fruit juices and wines. Due to the size-exclusion properties of polypyrrole, the thicknesses of the conducting polymer layers at both electrodes have to be equal to allow interfering compounds to be discriminated. Polypyrrole - glucose oxidase electrodes and polypyrrole - albumin electrodes with a polymer thickness of 750 mC cm-2 are used with a flow injection system with an electrochemical cell (details given). The rectilinear range of the calibration graph and the detection limit are dependent on the flux of the carrier stream, and both peak height and peak width decrease significantly with its velocity. At a carrier flux of 36 mL h-1, the peak width at half peak height for 10 mM glucose was 25 s, allowing 60 analyzes per h. Reliability of results and throughput of samples compares well with that of standard photometric procedures.

Abstract: The electrocatalytic oxidation of NADH at suitable electrode surfaces is of fundamental interest for the development of dehydrogenase-based enzyme electrodes. Copolymers of 3-(N-pyrrolo)-2,5,6-trichloro-1,4-benzoquinone or higher pyrrole-substituted chloranil derivatives with pyrrole and graphite/mediator electrodes with insolubilized phenazine and phenoxazine salts are investigated with respect to their electrocatalytic properties for the oxidation of NADH, their long-term operation stability, and the application in flow injection systems with enzyme columns or in enzyme electrodes with immobilized dehydrogenases.

Abstract: The voltammetric behavior of nifuroxime was investigated comparing stationary voltammetric methods with the recently proposed sequential-injection stripping analysis (SISA), by using cyclic voltammetry (CV) and differential-pulse voltammetry at bare and DNA-modified glassy carbon (GC) electrodes. In cyclic voltammetry, reduction of nifuroxime at DNA-modified electrodes gives rise to a well-defined peak, and in contrast to bare GC surfaces, a re-oxidation peak could be observed. Optimization of the pre-concentration process at the DNA-modified surface led to a significant enhancement of the voltammetric current response, a better defined peak shape and an improved dynamic range. Based on this optimized voltammetric procedure, SISA has been evaluated for the determination of nifuroxime. The flow-system significantly facilitates the regeneration of the DNA-modified electrode surface, hence diminishing problems related to accumulation and memory effects. The linear detection range could be extended to 65 µM with a detection limit (3 s) of 0.68 µM, which corresponds to an absolute amount of 21 ng nifuroxime.

Abstract: A fully automatic sequential injection system, named OLGA, for the online control of fermentation processes is described. It consisted of a sampling and injection section with a high-precision, stepping motor-driven micropump, magnetic snap valves and two manifolds manufactured in polyacryl and a detection section equipped with a low-volume, four-electrode flow-through detection cell. The detection cell was fitted with two Pt working electrodes (0.5 mm diameter) to monitor H2O2 at 650 mV vs. Ag/AgCl and Ag pseudo-reference electrodes. The flow system was controlled by a computer program written in Microsoft Visual Basic 3.1 Professional and operated within the Windows 3.1 environment. The software package allow automatic calibration and recalibration with up to five standard solutions, calculation of the analyte concentration using the most recent calibration data and the injection of samples from up to 4 sampling sites. The system was evaluated for the determination of glucose and the simultaneous determination of glucose and lactate. Enzyme membranes containing immobilized glucose oxidase or lactate oxidase were mounted over the working electrodes. A carrier stream of 0.1 M sodium phosphate buffer of pH 7.4 was used with a injection volume of 3-5 µL. The OLGA system was also applied to monitor glucose concentration in a baker`s yeast fermentation for up to 35 h.