Determination of α-tocopherol in low-density polyethylene (LDPE) films by diffuse reflectance Fourier transform infrared (DRIFT-IR) spectroscopy compared to high performance liquid chromatography (HPLC) Original Research Article

Quantification of α-tocopherol (α-T) from plastics is currently performed by high performance liquid chromatography (HPLC) with fluorescence detection, which requires solvent extraction of α-T from the films. This stage is very time consuming and has the risk of incomplete extraction or α-T degradation. In this work, a non-destructive analytical method for quantification of α-T in low-density polyethylene (LDPE) films by diffuse reflectance Fourier transform infrared (DRIFT-IR) spectroscopy was developed. Standard films were fabricated to give a final concentration of α-T from 0.13 to 1.74% as quantified by an HPLC method (C18 columns with an isocratic elution with methanol:water (98:2) and fluorescence detection). HPLC analyses were performed by extracting the antioxidant from the films with tetrahydrofuran (THF) stabilized with BHT under controlled laboratory conditions (low-room temperature, light protection and cooled solvents). DRIFT-IR spectra were obtained for the standard films. The phenolic (C–OH) group vibration at 1209 cm−1 was used to quantify the α-T concentration. The LDPE band at 2019 cm−1 was used as internal standard. The ratio of the band heights (or areas) at 1209 cm−1/2019 cm−1 was used for quantification. Determination coefficients of 0.9997 and 0.9988 were obtained from the height and area ratio calibration curves (model equations), respectively. The predictive ability of the models were validated using the leave-one-out cross-validation approach based on the results from the solvent extraction and HPLC quantification technique performed under controlled laboratory conditions. This work is a response to a demand for analytical techniques that can be performed in a short time, are non-destructive, do not require solvents, and for which there is no need for controlled laboratory conditions.