Letter | Published:

A Colour Reaction of Vitamin E with Vitamin K and Cysteine


A FEW crystals of vitamin K (2-hydroxy-3-methyl-1,4-naphthoquinone) and of cysteine (chorhydrate) are added to a solution containing 7–20 µgm./ml. of vitamin E (sodium phosphate of alpha-tocopherol). The solution is heated up to boiling point. About one minute after boiling the solution takes a blue tint. The intensity of colour is proportional to the content of vitamin E and increases during the following three minutes, finally rendering the solution opaque.

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