Colorimetric determination of tocopheryl acetate (vitamin E) in pure form and in multi-vitamin capsules

A simple, accurate and sensitive method for the determination of micro amounts of vitamin E (V(E)) in pure form and in multi-vitamin capsules is described. The method is based on the reduction of tetrazolium blue in slightly alkaline medium by vitamin E after extraction from aqueous EDTA medium with petroleum ether and transesterification. The oxidation reduction reaction occurs after 10 min of heating in a water bath at 90+/-2 degrees C, leading to the formation of a highly coloured formazan derivative. Different variables affecting the colour development were investigated and optimized. Absorbance measurements were made at 526 nm and the calibration graph was linear for 0.2-11.0 microg/ml of (V(E)) with relative precision of about 0.7-1.5% when the standard additions method is used.