Rapid determination of sterols in vegetable oils by CEC using methacrylate ester-based monolithic columns.

A method for the determination of sterols in vegetable oils by CEC with UV-Vis detection, using methacrylate ester-based monolithic columns, has been developed. To prepare the columns, polymerization mixtures containing monomers of different hydrophobicities were tried. The influence of composition of polymerization mixture was optimized in terms of porogenic solvent, monomers/porogens and monomer/crosslinker ratios. The composition of the mobile phase was also studied. The optimum monolith was obtained with lauryl methacrylate monomer at 60:40% (wt:wt) lauryl methacrylate/ethylene dimethacrylate ratio and 60 wt% porogens with 20 wt% of 1,4-butanediol (12 wt% 1,4-butanediol in the polymerization mixture). Excellent resolution between sterols was achieved in less than 7 min with an 85:10:5 v/v/v ACN-2-propanol-water buffer containing 5 mM Tris at pH 8.0. The limits of detection were lower than 0.04 mM, and inter-day and column-to-column reproducibilities at 0.75 mM were better than 6.2%. The method was applied to the determination of sterols in vegetable oils with different botanical origins and to detect olive oil adulteration with sunflower and soybean oils.

Classification of vegetable oils according to their botanical origin using sterol profiles established by direct infusion mass spectrometry.

A simple and quick method to classify vegetable oils according to their botanical origin, based on direct infusion of sterol extracts into a mass spectrometer, was developed. Using mass spectrometry (MS) with either an electrospray ionization or an atmospheric pressure photoionization source, followed by linear discriminant analysis of the mass spectral data, oil samples corresponding to eight different botanical origins were perfectly classified with an excellent resolution among all the categories. An excellent correlation between the sterol profiles obtained by MS and by the official gas chromatography (with flame ionization detection) method was obtained. Thus, the proposed method is a promising alternative for sterol fingerprinting of vegetable oils, with the advantage that prior chromatographic separation is not required.

Determination of tocopherols in vegetable oils by CEC using methacrylate ester-based monolithic columns.

The separation and determination of tocopherols (Ts) in vegetable oils by CEC using methacrylate ester-based monolithic columns has been developed. The effects of pore size of the monolithic columns were studied, and the composition of mobile phase was optimized. The optimal pore size of the monolith was obtained with 12 wt% 1,4-butanediol in the polymerization mixture. Excellent resolution between tocopherols was achieved within 10 min analysis time with a 99:1 v/v MeOH-aqueous buffer containing 5 mM tris(hydroxymethyl)aminomethane at pH 8.0. The LODs were lower than 2.3 microg/mL, and interday and column-to-column reproducibilities at 25 microg/mL were better than 5.6%. Using a 93:7 v/v MeOH-aqueous buffer, both tocopherols and tocotrienols (T(3)s) of grapeseed and palm oils were resolved. Application to the detection of olive oil adulteration with low-cost edible oils was demonstrated.

Classification of vegetable oils according to their botanical origin using amino acid profiles established by direct infusion mass spectrometry.

Amino acid profiles, established by direct infusion mass spectrometry, have been used to classify vegetable oils according to their botanical origin. The proteins present in hazelnut, sunflower, corn, soybean, olive, avocado, peanut and grapeseed oils were precipitated with acetone, and the residue was hydrolyzed in acid medium, diluted in a hydrochloric acid/ethanol mixture, and infused into the mass spectrometer. The spectra of the hydrolyzed protein extracts showed [M+H]+ ions of the following amino acids: glycine, alanine, serine, proline, valine, threonine, cysteine, isoleucine + leucine, aspartic acid, lysine, glutamic acid, methionine, histidine, phenylalanine, arginine and tyrosine. These ions were used to construct linear discriminant analysis (LDA) models. The ratios of the ion signal intensities selected by pairs were used as predictors. With the sequential application of three LDA models, the eight botanical origin categories of the samples were well resolved.