Evaluation of a Carbon Ink Chemically Modified Electrode Incorporating a Copper-Neocuproine Complex for the Quantification of Antioxidants

Abstract A feasibility study on the use of a carbon ink chemically modified electrode to quantify antioxidants, containing [Cu(Nc)2](NO3)2. First, [Cu(Nc)2](NO3)2 was prepared and characterized, to demonstrate similarity with electrochemical response of CUPRAC solution. Then, the Chemically Modified Electrode (CME) was prepared with [Cu(Nc)2](NO3)2 and it was used to determine the total antioxidant content (TAC), employing Trolox, as a variation of the CUPRAC methodology in order to provide an alternative to the original methodology, which requires the preparation of several precursor solutions. CME also demonstrated reproducible results in the quantification of TAC for different antioxidants, where the anodic peak current of the cyclic voltammograms of the adsorbed [Cu(Nc)2]2+ showed a linear correlation with the antioxidant concentration. Those results resemble results obtained in CUPRAC solution, the characteristic calibration curve slopes can also be employed to determine the relative number of exchanged electrons. Analytical performance of the prepared CME referred to Trolox as probe lead to the following parameters: quantification limit of 2.10 × 10-4 mol L-1; detection limit of 6.29 × 10-5 mol L-1; and a linear range of 2.10 to 77.4 (x 10-4) mol L-1. Finally, analytical performance of this CME was also evaluated with Ascorbic Acid and Catechin as sample antioxidants. TAC determinations were performed in tea samples and the results were comparable to those obtained using the conventional spectrophotometric CUPRAC method. Obtained results suggest that this CME can be reused in consecutive determinations, as long as a previous calibration curve is prepared for the electrode on a regular basis.