A simple and sensitive reduced graphene oxide-modified glassy carbon electrode-based electrochemical sensor was used for the concomitant determination of gallic acid (GA) and protocatechuic (PA) acid. The prepared sensor showed a significant enhancement in synergetic electro-catalytic performance towards GA and PA oxidation. A good resolution of the voltammetry peaks was obtained and a method of square wave voltammetry was developed for detection. The modified electrode was characterized by electrochemical techniques. The optimal experimental parameters were considered. GA and PA exhibited a linear increase in the peak currents with their concentrations in the range from 20 to 144 µmol·L−1 for GA and from 20 to 166 µmol·L−1 for PA, with limits of detection (S/N = 3) of 30.8 µmol·L−1 for GA and 10.2 µmol·L−1 for PA. The sensor applicability was simultaneously tested for the analytical determination of GA and PA in mango juice and exhibited a robust functionality.
SummaryA simple and sensitive poly(gallic acid)/multiwalled carbon nanotube modified glassy carbon electrode (PGA/MWCNT/GCE) electrochemical sensor was prepared for direct determination of the total phenolic content (TPC) as gallic acid equivalent. The GCE working electrode was electrochemically modified and characterized using scanning electron microscope (SEM), cyclic voltammetry (CV), chronoamperometry and chronocoulometry. It was found that gallic acid (GA) exhibits a superior electrochemical response on the PGA/MWCNT/GCE sensor in comparison with bare GCE. The results reveal that a PGA/MWCNT/GCE sensor can remarkably enhance the electro-oxidation signal of GA as well as shift the peak potentials towards less positive potential values. The dependence of peak current on accumulation potential, accumulation time and pH were investigated by square-wave voltammetry (SWV) to optimize the experimental conditions for the determination of GA. Using the optimized conditions, the sensor responded linearly to a GA concentration throughout the range of 4.97 × 10−6 to 3.38 × 10−5 M with a detection limit of 3.22 × 10−6 M (S/N = 3). The fabricated sensor shows good selectivity, stability, repeatability and (101%) recovery. The sensor was successfully utilized for the determination of total phenolic content in fresh pomegranate juice without interference of ascorbic acid, fructose, potassium nitrate and barbituric acid. The obtained data were compared with the standard Folin–Ciocalteu spectrophotometric results.
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