Electrochemical Impedance Spectroscopy as a Tool To Investigate the Electrochemical Behavior of Beetroot and Spinach...

The increasing demand for rapid and reliable methods to characterize the electrochemical behavior of plant-derived bioactive materials has motivated the exploration of alternative electroanalytical approaches. In this study Electrochemical Impedance Spectroscopy (EIS) is employed as the primary analytical tool to characterize interfacial properties of carbon paste electrodes (CP) modified with beetroot (BET) and spinach (SPI) extracts. Impedance parameters were extracted using equivalent circuit modeling and correlated with the antioxidant composition of the extracts. Modification with beetroot extract led to a pronounced decrease in the primary charge-transfer resistance from 6.94 × 10⁵ Ω (CP) to 2.72 × 10⁴ Ω (BET), indicating facilitated interfacial electron-transfer processes associated with betalain-rich layers. In contrast, the spinach-modified electrode exhibited a higher charge-transfer resistance (9.90 × 10⁶ Ω) and a diffusion-controlled impedance response, consistent with the formation of a more resistive interfacial film. The results demonstrate that EIS provides distinct and reproducible impedance signatures for extract-modified electrodes, reflecting differences in interfacial charge-transfer kinetics, capacitive behavior, and mass-transport limitations. This work highlights the usefulness of EIS for characterizing the electrochemical interfacial behavior of electrodes modified with plant-derived extracts.