Determination of isopropylmethylphenols in black seed oil by differential pulse voltammetry

A differential pulse voltammetric method is presented for the determination of isopropylmethylphenols (carvacrol and/or thymol) in phytotherapeutic black seed oils. The voltammetric behaviours of these phenols were examined in various buffer systems over the pH range 3.5-10.0. In Sörensen buffered methanol solution (3:7; v:v; pH 8.5), the differential pulse voltammograms exhibited reproducible peaks at Ep + 0.49 V vs. silver-silver chloride-potassium chloride 3 M for both carvacrol and thymol. Under these conditions, a plot of peak height against concentration of the isopropylmethylphenols was found to be linear over the range 0.25-2.5 microg/mL (r = 0.999). The detection limit was 0.04 microg/mL. The described voltammetric method was tested on two black seed oils available on the Austrian market.