Sensitive voltammetric determination of thymol in essential oil of Carum copticum seeds using boron-doped diamond electrode

Abstract

Essential oil of Carum copticum seeds, obtained from a local shop, was extracted and content of thymol was analyzed using square-wave voltammetry at boron-doped diamond electrode. The effect of various parameters, such as pH of supporting electrolyte and square-wave voltammetric parameters (modulation amplitude and frequency), was examined. In Britton-Robinson buffer solution (pH 4), thymol provided a single and oval-shaped irreversible oxidation peak at +1.13 V versus silver/silver chloride potassium electrode (3 M). Under optimal experimental conditions, a plot of peak height against concentration of thymol was found to be linear over the range of 4 to 100 mu M consisting of two linear ranges: from 4 to 20 mu M (R-2 = 0.9964) and from 20 to 100 mu M (R-2 = 0.9993). The effect of potential interferences such as p-cymene and gamma-terpinene (major components in essential oil of C copticum seeds) was evaluated. Thus, the proposed method displays a sufficient selectivity toward thymol with a detection limit of 3.9 mu M, and it was successfully applied for the determination of thymol in essential oil of C copticum seeds. The Prussian blue method was used for validation of the proposed electroanalytical method.