INFLUENCE OF GRAPHITE POWDER, ADDITIVES AND ENZYME IMMOBILIZATION PROCEDURES ON A MEDIATORLESS HRP-MODIFIED CARBON-PASTE ELECTRODE FOR AMPEROMETRIC FLOW-INJECTION DETECTION OF H2O2

The behaviour of horseradish peroxidase modified carbon paste electrod es (HRP-CPEs) for mediatorless amperometric flow-injection (FI) detect ion of hydrogen peroxide is described. The influence of various commer cially available graphite powders and additives was studied, using ads orption and covalent binding (at different pHs) as enzyme immobilizati on techniques. The HRP-CPE was used as the working electrode in an FI system. An optimal applied potential for electrocatalytic reduction of H2O2 was found at -50 mV vs. Ag/AgCl (0.1 M KCl). The highest sensiti vity (approximate to 78 mu A cm(-2) mM(-1)) obtained in the FI made wa s observed for electrodes made of graphite powder having the highest s urface area, with HRP immobilized by adsorption (at pH 8) in the prese nce of lactitol as enzyme stabilizer. The lowest detection limit (appr oximate to 0.1 mu M) was noted for HRP-CPE incorporating the graphite powder having the lowest background current.