Colorimetric determination of peroxidase activity in the presence of a polyanion

A procedure was developed for the determination of peroxidase activity with respect to substrates whose oxidation products were insoluble or poorly soluble in the reaction medium. It was demonstrated that the introduction of water-soluble sulfonated polystyrene to a reaction medium containing aniline and hydrogen peroxide made it possible to transform insoluble polyaniline to the highly dispersed state, preventing the formation of a deposit at the walls of the cuvette in the course of analysis. The addition of sulfonated polystyrene to the reaction medium improves the sensitivity of the determination of horseradish peroxidase.