Abstract
Highly specific and sensitive, the proposed fluorometric method for determining α-tocopherol is robust and fairly fast. Ithas been tested in parallel with a conventional thin layer chromatographic method on foods and feeds. The only necessarycleanup is the usual saponification. The unsaponificable fraction can be extracted with ethyl ether or, preferably, withExtrelut columns. Reagents and their solvents are added to the isooctane solution before each successive reaction and arethen eliminated by partition with water. The α-tocopherol (α-T) derivative always remains in isooctane. The first step isnitrosation and elimination of tocopherols and tocotrienols other than α-isomers. α-T is then oxidized to α-tocored (α-TR)with a mixture of sulfuric acid, ferric chloride, and iodine bromide. Α-TR is then condensed to a new reagent: 4,5-dimethylo-phenylenediamine. The phenazine formed is strongly fluorescent. Iodine and bromine add to the double bonds of α-tocotrienol present and quench the fluorescence of its phenazine.
Highlights
The determination of vitamin E in food or feedstuffs poses a difficult problem
liquid chromatography (LC) is faster than conventional methods, the separation of α-T in complex mixtures such as foods and feeds require 20 min or more
We found that a mixture of sulfuric acid, ferric chloride, and iodine bromide, dissolved in ethanol in given proportions, is able to form α-TR
Summary
The determination of vitamin E in food or feedstuffs poses a difficult problem. Eight natural homologs possess a vitamin activity: 4 tocopherols and 4 tocotrienols. Α-T is by far the most active compound. It is generally agreed that α-T accounts for about 80% of vitamin E supply in foods. It is the only homolog used in modern feeding. The other homologs have lower activities and it is difficult if not impossible to determine them all. As well as various substances, interfere in the determination of α-T
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