Determination of trace amounts of thymol and caffeic acid in real samples using a graphene oxide nanosheet modified electrode: application of experimental design in voltammetric studies

Abstract

A graphene oxide nanosheet modified glassy carbon electrode (GO/GCE) was used for the determination of thymol (Thy) and caffeic acid (CA). The GO-based sensor was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The oxidation peak current of the Thy and CA was determined in a 0.2 M Britton–Robinson (B–R) buffer solution and optimized by experimental design. A central composite rotatable design (CCRD) was used to evaluate the effects of the variables in the differential pulse voltammetry method (DPV). These variables include instrumental and experimental parameters. Under the optimized conditions the dynamic range for Thy and CA was from 2.0 to 200.0 μM and 1.5 to 270.0 μM and the detection limits were found to be 6.5 × 10⁻⁸ M and 2.5 × 10⁻⁹ M for Thy and CA, respectively. The electron transfer coefficient (α) as a kinetic parameter was also determined for the Thy and CA oxidation process. The results revealed that the modified electrode shows an improvement in anodic oxidation activity of Thy and CA due to a marked enhancement in the current response compared with the bare GCE. The modified electrode demonstrated good sensitivity, selectivity and stability. The prepared electrode was applied for the determination of Thy and CA in real samples such as a thyme plant and a eucalyptus inhaler drop.