Electrochemical quantification of thymol in Thymus vulgaris essential oil with a 3D-printed electrode

Thymol (TM), a monoterpenoid phenol with diverse antioxidant and antimicrobial properties, is of significant interest to the pharmaceutical, food, and agricultural sectors. Due to its importance, this study developed an electrochemical method for its quantification using a 3D-printed electrode made from a conductive carbon black/PLA filament (CB/PLA electrode). Electrochemical measurements were performed using square-wave voltammetry (SWV) in 0.1 mol L⁻1 Na2SO4 (pH 13). The potential was scanned from 0 to +0.80 V, exploiting the oxidation process of TM at approximately +0.30 V (vs. Ag|AgCl|KCl(sat.)). Under the optimized SWV conditions, a linear response was obtained in the concentration range of 75.00 to 337.50 µg/mL (r = 0.99). The proposed method demonstrated excellent analytical characteristics, including high stability (RSD < 9%; n = 6) and a satisfactory recovery value (89%). These results suggest minimal matrix interference, confirming the method's accuracy for analyzing real samples. This work highlights that the combination of 3D-printed electrodes and the SWV technique offers a selective approach for TM analysis. The reliability of the proposed method for quality control in thyme essential oil is confirmed, presenting a promising strategy for monitoring other bioactive compounds with a rapidly manufactured, reproducible, and low-cost electrode.