Flow Injection Analysis of Antioxidant Capacity Based on Biamperometric Detection by Interdigitated Electrode

The aim of this study was the development of an electrochemical method for the flow injection analysis of antioxidant capacity, based on continuous enzymatic production of ABTS&middot ; + and biamperometric detection by interdigitated electrode (IDE). In this study ABTS&middot ; +│ ABTS redox couple was used as indicating redox pair. ABTS&middot ; + radical cation represents an oxidized form while ABTS is a reduced form of the redox pair. During the analysis, continuous one electron oxidation of 2, 2’ -azino-bis(3-ethylbenzothiazoline-6-sulfonic-acid) (ABTS) into corresponding radical cation ABTS&middot ; + (Eq. (1)) was achieved by peroxidase-catalyzed reaction in the flow-through tubular reactor. (1) Enzymatically produced ABTS&middot ; + react in the mixing coil with different compounds of antioxidant AH (analyte) producing ABTS according to reaction (2). ABTS&middot ; + + AH → ABTS + A&middot ; + H+ (2) After reaction, ABTS&middot ; + concentration was reduced. In the proposed biamperometric measurement by IDE, current intensity is proportional to the residual reduced concentration of ABTS&middot ; + after reaction with an antioxidant. The performance of bioreactor was tested at different concentrations of immobilized enzyme, ABTS and hydrogen peroxide. The influence of flow rate on proper operation of the bioreactor was also studied. The results of antioxidant activity were determined using Trolox as a standard. The applied IDE detector accomplished good sensitivity of 0.3 nA/&micro ; M of Trolox and offered linear range between 20 &micro ; M to 500 &micro ; M of Trolox. The comparison of results (R2 = 0.9915) for antioxidant activity between spectroscopic and FIA biamperometric measurements by interdigitated electrodes confirmed the applicability of the proposed method for determination of antioxidant capacity.