Abstract: A polished Pt disc electrode was modified by the electropolymerization of dibenzo-18-crown-6 (DB-18-C-6) on to its surface using an applied potential of +3.2 V (vs. Ag/AgCl) for 5 min in an electrolyte containing 0.025 M DB-18-C-6 and 200 mM tetrabutylammonium tetrafluoroborate. The modified electrode and a Ag/AgCl reference electrode were mounted in a thin-layer flow cell of a FIA system. The potentiometric response of the electrode to catechol and catecholamine was measured using a 20 µL injection loop and 0.1 M potassium phosphate buffer of pH 9.4 as the mobile phase (1 ml/min). The calibration graph was linear for 1 µM to 10 mM catechol and the detection limit was 0.5 µM. Similar results were obtained for the neurotransmitters. Interferences from ascorbic acid and uric acid were not significant until the concentration of the interferent exceeded a 10-fold excess.

Abstract: A new method of amperometric determination of phenolic compounds using an enzyme electrode is proposed. The latter represents the combination of the oxygen electrode and immobilized laccase. Analytical systems of flow injection and batch types were considered. A method of immobilization was developed that provided an increase in the stability of the enzyme. Optimal conditions for biosensor operation were found. The time needed for analysis in the flow injection mode was below 100 s. A column with immobilized enzyme could be used for up to 500 determinations of phenolic compounds without decrease of the enzyme activity. The practical validity of the method was demonstrated by tannin analysis in tea of different brands.

Abstract: A review with many references. Enzyme modified carbon paste electrodes (CPEs) opens up a new way to the reagentless anal. of food and environmental samples as well as bioprocess media. Enzymes, cofactors, redox mediators and additives were immobilized at graphite particles suspended in an organic solvent. Short response times and low background currents were achieved. Peroxidase modified CPEs detect hydrogen peroxide in the range between 0.1 µM and 0.5 mM. Bienzyme modified CPEs were produced by coimmobilization of horseradish peroxidase or fungal peroxidase with oxidases, e.g. lactate oxidase and pyruvate oxidase to detect their substrates selectively at low potentials at -50 - +100 mV vs. Ag/AgCl in the micro- and millimolar range. The sensitivity and the operational stability of the bienzyme electrodes can be improved considerably by adding cationic polyelectrolytes, e.g. polyethylenimine, poly-L-lysine, poly-L-arginine alone or in combination with trehalose and lactitol. Tyrosinase modified CPEs detect phenols with free ortho-positions and dihydroxybenzene derivatives This CPEs were mounted into a flow through cell and combined with a membrane extraction enrichment step. Under FIA (flow injection anal.) conditions phenol and catechols can be determined in the ranges from 10 nM to 10 µM with and from 0.5 µM and 1 mM without enrichment. The membrane extraction step allows the direct anal. of surface and ground water. A D-lactate selective CPE was constructed by coimmobilization of D-lactate dehydrogenase. NAD+ and toluidine blue O bound on polymer backbone. D-lactate and NADH are detectable at -50 mV vs. Ag/AgCl. D-lactate was detected in the range between 20 µM and 20 mM.