Determination of catalase-like activity in plants based on the amperometric monitoring of hydrogen peroxide consumption using a carbon paste electrode modified with ruthenium(IV) oxide

A carbon paste electrode containing ruthenium(TV) oxide as a modifier was tested as an effective hydrogen peroxide amperometric sensor in bulk measurements (hydrodynamic amperometry). Factors that influence its overall analytical performance, such as pH and the applied potential, were examined. The RuO2-modified electrode displayed high sensitivity towards hydrogen peroxide, with detection limits as low as 0.02 mm at pH 7.4 and 0.007 mm at pH 9.0. The method was applied for monitoring the decomposition of hydrogen peroxide (by catalase) in phosphate buffer of pH 7.4. The relative response of the electrode towards ascorbic acid was assessed and it was found that the selectivity of the RuO2-modified electrode towards hydrogen peroxide over ascorbic acid could be significantly improved by electro-polymerizing m-phenylenediamine on its surface prior to measurements. The RuO2-modified electrode was used for the kinetic (fixed time) determination of catalase activity in the range of 4-40 U/mL (detection limit 1.2 U/mL). The method was applied to the determination of catalase-like activity in various plant materials (recovery ranged from 93 to 101%, detection limit 480 U/100 g). Copyright (c) 2006 John Wiley & Sons, Ltd.