Vitamin E determination in edible oils by reversed-phase dispersive liquid-liquid microextraction and screen-printed carbon electrodes

A novel simple, environmentally friendly and portable method to determine vitamin E in edible oils based on reversed-phase dispersive liquid-liquid microextraction combined with electrochemical detection using screen-printed carbon electrodes (SPCEs) has been developed. Vitamin E was extracted from oil samples into a 4 M HCl aqueous solution and determined by differential pulse voltammetry using SPCEs. The extraction conditions optimized by experimental design (i.e., Plackett-Burman and central composite designs) were: aqueous 4 M HCl extractant volume, 43 mu L; extraction time, 2 min; centrifugation time, 10 min; and centrifugation speed, 3000 rpm. The proposed method requires a standard addition calibration approach, and the working range showed good linearity from 0 to 20 mg L- 1, with a correlation coefficient ranging from 0.990 to 0.995 (N=5). The method-ological limit of detection was between 1 and 3 mg L- 1. The repeatability of the proposed method was evaluated at 15 mg L- 1, and the relative standard deviation ranged between 10 and 15% (n=5). For the quantification of vitamin E in ten commercial samples of olive, sesame, soybean, sunflower and a mixture of sunflower and corn oils, the volume of the extractant phase (i.e., 4 M HCl aqueous solution) was increased up to 100 mu L and satisfactory recoveries were obtained in the range of 85-115%, confirming the applicability of the method.