DIRECT ELECTROCATALYTIC DETERMINATION OF DISSOLVED PEROXIDASES

A novel voltammetric approach is described for the quantification of d issolved redox enzymes. The measurement of horseradish peroxidase and microperoxidase is based on the electrocatalytic current generated whe n the enzyme reduces hydrogen peroxide to water and oxidises at low po tential a mediator which is regenerated in a cathodic electrode reacti on. Since the mediator regeneration is sufficiently fast, the overall reaction rate is determined by the enzyme activity. As a consequence s tationary current-time curves are obtained in dependence on the activi ty of peroxidase in solution. For the chemical modification the electr ode was modified with 1-(N,N-dimethylamine)-4-(4-morpholine)be a media tor of low solubility in reduced form and with favourably low formal p otential. At a working potential of -50 mV vs, 0.1 M Ag/AgCl cathodic steady-state currents were obtained after injection of peroxidase in t he presence of 1 mmol/l hydrogen peroxide. The detection limit for hor seradish peroxidase and microperoxidase-11 were 10 ng/ml (250 pmol/l) and 20 ng/ml (10 nmol/l), respectively.