Voltammetric Determination of Tannic Acid in Medicinal Plants Using Multi-Walled Carbon Nanotube-Modified Electrode

Abstract

Tannins are a class of natural phenolic antioxidants represented by oligomers and polymers. Tannic acid (gallotannin) (TA) is one of the most typical compounds widely distributed in plants. It has a wide application area in food technology and as a part of traditional herbal medicine in the treatment of various diseases. TA is one of the standards used in medicinal plant quality control for plants rich in tannins. Therefore, the development of sensitive and simple methods for TA quantification is of practical interest. Glassy carbon electrode modified with multi-walled carbon nanotubes (GCE/MWCNTs) has been developed for the determination of TA in medicinal plants. An improvement in TA voltammetric response has been achieved using modified electrode due to the high electroactive surface area and electron transfer rate vs. bare electrode. TA electrooxidation at the GCE/MWCNTs is an irreversible surface-controlled process involving the transfer of two electrons and two protons in the first step. In differential pulse mode using Britton–Robinson buffer pH 2.0 as the supporting electrolyte, a linear dynamic range of 0.10–7.5 μM with a detection limit of 0.038 μM has been obtained. The method has been applied for the analysis of infusions and decoctions of tannin-containing medicinal plants and compared to the spectrophotometric method. A positive correlation has been observed with ferric reducing power reflecting the total content of phenolic compounds in the sample.

Keywords

• voltammetry
• chemically modified electrodes
• carbon nanotubes
• phenolic antioxidants
• tannic acid
• medicinal plants