The distribution of vitamin A between light petroleum and aqueous methyl alcohol

THE difference in behaviour on partition between light petroleum and 80-90 % aqueous methyl alcohol has for long provided a useful means of differentiation and separation of the hydrocarbon carotenoids from the corresponding hydroxylated compounds-the xanthophylls [Kraus, 1872; Borodin, 1883; WilLstatter & Stoll, 1913]. The separation and extraction of carotenoids by this partition method can be controlled visually by the colour of the extract, but in analyses of biological materials containing carotenoids and vitamin A such as we have recently carried out on butter [Gillam et al. 1933], egg yolk [Gillam & Heilbron, 1935], and blood serum [Gillam & El Ridi, 1935], the question sometimes arises as to which phase contains the vitamin, which is, of course, colourless. In the analysis of butter it has usually been found that the vitamin A is divided between the petrol and alcohol phases rather irregularly, although Wolff et al. [1930] have shown that carotene and vitamin A can be separated by means of the phase test, the carotene going into the petrol phase whilst the vitamin goes into the alcohol phase. As however, the exact conditions for complete extraction were not speci- fied and vitamin A has no colour by which its extraction can be followed visually, we have carried out a series of determinations of the partition coefficient of vitamin A between light petroleum and various accurately known concentrations of aqueous methyl alcohol, the conditions being strictly controlled.