Rapid Determination of alpha-Tocopherol in Vegetable Oils by Fourier Transform Infrared Spectroscopy

The aim of this study was to develop a rapid methodology for the analysis of alpha-tocopherol in vegetable oils as an alternative to the high-performance liquid chromatography (HPLC) methods: Fourier transform infrared (FT-IR) methodology. Thirteen vegetable oils (corn, peanut, soybean, sunflower and mixtures) commercially obtained were analysed by reverse-phase HPLC with fluorescence detection (FD) in order to obtain standard values for alpha-tocopherol. Validation tests were performed concerning the HPLC method. The HPLC method is valid for alpha-tocopherol analysis in the 1-90 mg/L linear range. Method repeatability was 3.6%, and accuracy results were within 70-95%. FT-IR spectra of the vegetable oils were acquired in the attenuated total reflection mode (45A degrees and 60A degrees crystals of ZnSe). To predict the alpha-tocopherol content in samples, calibration models were designed, and the partial least squares method was used to analyse data from FT-IR spectral region at 1,472-1,078 cm(-1). Results obtained showed that the calibration model implemented with a 45A degrees crystal is more suitable for the proposed analysis. Five extra samples of vegetable oils were analysed by HPLC/FD and by FT-IR. Using the calibration model implemented for FT-IR (45A degrees crystal), the alpha-tocopherol content in samples was determined. The results obtained by HPLC/FD and FT-IR were compared, and there were no significant differences among them. Results showed that FT-IR can be used as an alternative method for rapid screening of alpha-tocopherol in vegetable oils without sample pre-treatment.