Electrochemical determination of gallic acid in Camellia sinensis, Viola odorata, Commiphora mukul, and Vitex agnus-castus by MWCNTs-COOH modified CPE

Gallic acid (GA) is the main phenolic antioxidant which has been subjected of many studies because of its important biological properties including anticancer, anti-inflammatory and antimicrobial activities as well as free radicals scavenger and cardiovascular diseases protector. Hereupon, fabricating a selective and sensitive sensor for GA detection and measurement is an important issue. In this paper a carboxylated MWCNTs modified carbon paste electrode (MWCNTs-COOH/CPE) was successfully fabricated and employed for GA determination. Activating the carboxylic sites of the MWCNTs carried out in nitric acid solution in ultrasonic bath and further studied by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The electrocatalytic oxidation of GA at the MWCNTs-COOH/CPE surface was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. The GA presented a high electrochemical response on MWCNTs-COOH/CPE at pH 2 in comparison with the CPE. This sensor showed a linear response range of 0.33 - 196 µM and detection limit of 17.2 nM (S/N = 3). Furthermore, the designed MWCNTs-COOH/CPE was successfully applied as a electrochemical sensing system for GA determination in extracts of Camellia sinensis, Viola odorata L, Commiphora mukul, and Vitex agnus-castus respectively with estimated amount of 11.4, 8.9, 11.91 and 2.9 mg L-1 GA in each extract.