Voltammetric determination of condensed tannins with a glassy carbon electrode chemically modified with gold nanoparticles stabilized in carboxymethylcellulose

Abstract This paper reports the electroanalytical determination of condensed tannins in extracts of Acacia ( Acacia mearnsii de wild) using a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNPs) and carboxymethylcellulose (CMC). The AuNPs were synthesized by the reduction of chloroauric acid with sodium borohydride using CMC as a stabilizer. The characterization of the AuNPs was carried out by UV–vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The modified surface was characterized by scanning electron microscopy with field emission gun (SEM-FEG), atomic force microscopy (AFM) and profilometry experiments. Electrochemical studies were carried out by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square-wave voltammetry (SWV). The results show that the nanoparticles obtained are spherical and have an average diameter of 5.3 nm. The modified electrode was prepared by dropping the AuNPs-CMC dispersion onto the surface of the GCE. For the quantification of condensed tannins catechin was used as a model compound. The detection (DL) and quantification (QL) limits for catechin were 0.274 and 0.831 μmol L −1 , respectively. The proposed detector was tested by determining the total condensed tannins concentration in real samples using the standard addition method. The curves for the samples exhibited a slope similar to the calibration curve, indicating the absence of interference from the matrix components in the response to condensed tannins. The modified electrode was successfully applied to the analysis of real samples, with results comparable to those obtained using the Folin-Ciocalteu method. Thus, the strategy used in this study creates new opportunities for the sensitive detection of condensed tannins in plant extracts widely used in various industrial segments.