Voltammetric behavior and determination of tocopherols with partial least squares calibration:: analysis in vegetable oil samples

The voltammetric behavior of Vitamin E in the presence of olive oil is studied at the glassy carbon electrode, in a hexane-ethanol medium, with diverse techniques: sampled DC, differential pulse, and square-wave voltammetry. The influence of such variables as the hexane-ethanol proportion. sulfuric acid concentration, and instrumental parameters is studied. Separate voltammetric peaks are obtained for alpha-tocopherol and delta-tocopherol, but the peaks for beta-tocopherol and gamma-tocopherol overlap. For the simultaneous determination of alpha-, beta + gamma-, and delta-tocopherols in vegetable oils by the PLS-1 multivariate calibration method, the results using sampled DC and DPV voltammograms are compared. The DPV voltammograms are found to be the best data set. The proposed method is applied to the determination of the tocopherols in different vegetable oil samples. The olive oil samples needed a prior cleaning stage by solid-phase extraction on silica cartridges. The results are very acceptable. (C) 2004 Elsevier B.V. All rights reserved.