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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 α-tocopherol and δ-tocopherol, but the peaks for β-tocopherol and γ-tocopherol overlap. For the simultaneous determination of α-, β+γ-, and δ-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.

The determination of folic acid and its two main serum metabolites, 5-methyltetrahydrofolic acid and tetrahydrofolic acid, has been accomplished using four-way data modelled by the third-order multivariate calibration methods unfolded and N-dimensional partial least-squares (U-PLS and N-PLS), in combination with the separate procedure known as residual trilinearization (RTL). The four-way data were acquired by following the photochemical reaction of these compounds by on line irradiation with a UV lamp. The excitation-emission matrices (EEMs) were recorded as a function of the irradiation time, using a fast scanning spectrofluorimeter. The method achieves selectivity from the different rates at which the corresponding photoproducts of the folic acid derivatives are formed and degraded. Several N-dimensional chemometric algorithms were used and the method was applied to the determination of these compounds in serum samples. The best algorithms to perform the multivariate calibration were U-PLS and N-PLS in combination with the separate residual trilinearization procedure, achieving the second-order advantage. The approach allows minimizing or eliminating traditionally time-consuming sample pre-treatments and can facilitate quantifying an analyte in its native environment.