Determination of α-tocopherol and α-tocopheryl acetate in diets of experimental animals: Study of stability in the diets

Abstract

A simple method is described which permits, avoiding saponification, α-tocopherol and α-tocopheryl acetate measurement in semi-synthetic diets for experimental animals by HPLC, with both UV and fluorescence detection. Phenyldodecane was chosen as internal standard with remarkable performances, and EDTA and BHT were added to prevent oxidation in aqueous and non-aqueous phases respectively. The mobile phase was methanol–water (94:6, v/v) at a flow-rate of 2 ml/min. Samples were homogenized and extracted twice with n-hexane by probe sonication. Extracts were evaporated to dryness and redissolved with chloroform–methanol (1:1, v/v). Validation parameters were studied between 25 ng and 6 μg for α-tocopherol and between 3 and 24.2 μg for α-tocopheryl acetate, which corresponds to the range of values in the existing diets. Results had correlation coefficients >0.99; recoveries >85%; R.S.D.<6%, so the method is adequate to control vitamin E intake in animals as well as vitamin E stability in food during storage.