Distillation that is carried out under a high vacuum in an apparatus so designed as to permit molecules escaping from the warm liquid to reach the cooled surface of the condenser before colliding with other molecules and consequently returning to the liquid and that is used in the purification of substances of low volatility (as in the separation of vitamin A and vitamin E from fish-liver oils)

From a market perspective, the interest in natural substances to be used in food products is higher than for synthetic ones. Natural substances of commercial interest are present in complex mixtures made up of a number of different molecules. This is the case of tocopherols obtained from soya sludge. Most of the substances that are present in soya sludge are molecules of high molecular weight and are thermally sensitive. These properties hinder the separation or puritication of substances through traditional methods, because they are decomposed when subjected to high temperatures.