MWNT-Based Electrode for the Voltammetric Quantification of Carvacrol

Glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWNTs) dispersed in anionic surfactant sodium dodecylsulfate (MWNTs/GCE) has been developed for the carvacrol quantification. The electrode modification provides electrocatalytic effect to carvacrol oxidation (the cathodic shift of the oxidation potential on 121 mV and 1.7-fold increase of the oxidation currents vs. GCE). The electrodes are characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The 8.4-fold higher effective surface area has been obtained for the modified electrode (75 +/- 2 mm(2)for MWNTs/GCE vs. 8.9 +/- 0.2 mm(2)for GCE). EIS data have shown 6-fold lower charge transfer resistance in comparison to GCE. The irreversible diffusion-controlled oxidation of carvacrol with participation of one electron and one proton has been proved. The parameters of electrooxidation have been calculated. Differential pulse voltammetric quantification in phosphate buffer pH 6.5 can be performed in the ranges of 0.1-25 and 25-150 mu M of carvacrol. The detection limit of 0.075 mu M has been achieved. The method developed has been successfully applied for the determination of total isopropylmethylphenols in oregano spices. The results obtained have been compared to independent spectrophotometric method data.