Electrochemical Approach to the Determination of Gallic Acid with Bismuth-Based Carbon Electrodes

The synergistic combination of bismuth and its compounds with the exceptional properties of single-walled carbon nanotubes (SWCNT) was investigated as a sensing platform for the sensitive detection of gallic acid and as a standard for the determination of total phenol. Four bismuth-based electrodes were used for this purpose: SWCNT with bismuth (SWCNT/Bi) or bismuth (III) oxide (SWCNT/Bi2O3) and bismuth or bismuth (III) oxide electrodeposited on a glassy carbon electrode (ELF/Bi and ELF/Bi2O3), which were morphologically characterized by scanning electron microscopy. Cyclic voltammetry in phosphate electrolyte at different pH values revealed that the SWCNT/Bi2O3 electrode exhibited optimal performance for the analytical determination of gallic acid at pH 3. Surface-active carbon nanotubes facilitate the adsorption and accumulation of gallic acid, while the addition of Bi2O3 improves electron transfer, resulting in a synergistic enhancement of the oxidation signal. Square-wave voltammetry with SWCNT/Bi2O3 electrodes also provided reliable and accurate results and proved to be suitable for the quantitative determination of gallic acid with wide linearity (0.2–80 µM) and sensitivities of 12.5, 2.35, and 0.385 µA µmol−1 dm3 for low, medium, and high concentration ranges, respectively. The limit of detection was 0.06 µmol dm−3. Finally, the electrode was successfully applied for gallic acid determination in various seeds.