Quantification of tocochromanols in vitamin E dietary supplements by instrumental thin-layer chromatography

Abstract

A variety of vitamin E dietary supplement capsules (DSC) based on different natural oils or synthesis products are currently found on the market whose vitamin contents need to be controlled before and after marketing. Here, we present an instrumental thin-layer chromatography (TLC) method which allows a direct determination of all tocopherols (T) and tocotrienols (T3) as well as α-tocopherol acetate simultaneously in one run with short analysis time. For this purpose, contents of the DSC were extracted, applied on silica gel 60 plates, and developed with n-hexane/ethyl acetate/acetic acid, 90:10:2 (v/v/v) as mobile phase. The UV scan of the plate at 293 nm was used for quantification based on the peak height. Following the scan, the plate was treated with 10% sulphuric acid in methanol which led to characteristic yellow-to-brown colouring of the tocochromanol spots which allowed to distinguish tocochromanols from matrix components with similar Rf values. In most cases, determined vitamin E contents matched well with the information listed on the label of the investigated DSC samples. The method is fast, easy to perform and gently treats the analytes as it requires no thermal treatment prior to quantification, which makes it suitable as a screening method.