Novel modified electrode with immobilized galvinoxyl radical for the voltammetric determination of antioxidant activity

Abstract

Galvinoxyl radical (GO) immobilized on the electrode surface has been used for the voltammetric determination of antioxidant activity for the first time. Immobilization of radical on glassy carbon electrode (GCE) provides improvement of the system reversibility as well as increase of the redox currents in comparison to GO reduction in solution. But sensitivity of response is insufficient for the antioxidant activity estimation. Application of GCE modified with dispersion of CeO2 nanoparticles (NP) in cationic surfactant cetylpyridinium bromide (CPB) medium (CeO2 NP-CPB/GCE) as a base for GO immobilization provide full reversibility of its reduction (redox currents ratio of 1.02 and peak potential separation of 80 mV) and 7-fold increase of the redox currents at physiological pH of supporting electrolyte. Electrode developed has been successfully applied for the voltammetric evaluation of natural phenolics antioxidant activity expressed as the EC50 parameter (effective concentration of the antioxidant providing 50% inhibition of GO) and antioxidant activity of herbal preparations (tinctures, infusions and decoctions) as relative GO inhibition. Antioxidant activity of natural phenolics is decreased as morin > quercetin = ferulic acid > gallic acid > tannin ≈ catechin. The results obtained agree well with data of standard spectrophotometric method. The advantages of the method developed are 4-fold lower incubation time, less consumption of the reagents and the absence of limitations for colored samples.