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

Abstract

The aim of this study was to develop a rapid methodology for the analysis of α-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 α-tocopherol. Validation tests were performed concerning the HPLC method. The HPLC method is valid for α-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 (45° and 60° crystals of ZnSe). To predict the α-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 45° 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 (45° crystal), the α-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 α-tocopherol in vegetable oils without sample pre-treatment.