Electroanalysis at ultramicroelectrodes of oils and fats - Application to the determination of Vitamin E

Differential pulse voltammetry at ultramicroelectrode (UME) has been applied to the determination of Vitamin E concentration in vegetable oils and fats mixed with solvent at 60 degreesC. The use of UME permits a low proportion of solvent in solution. The solvent was N-methyl-pyrrolidone in which the concentration of quaternary ammonium salt used as supporting electrolyte must be less than 0.01 M in order to prevent the formation of two non-miscible phases. Only one oxidation peak was observed by differential pulse voltammetry. This peak was attributed to the oxidation of all the tocols which constitute Vitamin E and which are not separately analysed by this method. a-Tocopherol was used as added standard in the determination of the global concentration of Vitamin E. Several commercial vegetable oils and pork lards were electroanalysed. This analytical method gives a good estimation of the total amount of Vitamin E compared with chromatographic results. In pork lards, the quantities measured are in the range 5 x 10(-5) to 1 x 10(-4) M. Lards arising from pork which had received a-tocopherol supplement diet can be detected. (C) 2001 Elsevier Science B.V. All rights reserved.