An Improved Method for Determination of Blood Carotene.

Abstract

Following closely upon the rapid accumulation of our knowledge regarding the relation of plant carotene to vitamin A, increasing interest has been manifested by investigators in the study of carotenoids. Thus far the investigations have been concerned chiefly with the carotene content of human and animal organism under different physiological and pathological conditions. The need of a suitable method for determining small amounts of carotene in the circulating blood has become quite apparent. The methods hitherto employed are more or less unsatisfactory in that they are impractical or non-specific. In some, fairly large amounts of blood are required for each estimation, which makes serial determinations difficult or impossible. Others are not specific and may lead to false results when they are used in the presence of other similarly reacting substances. The methods which involve the use of the yellow color of the carotin dye itself as an agent in the determination do not take into consideration that polyene dyes other than the carotenes, for example those of the xanthophyll type, may be part of the food intake and enter the blood. As a matter of fact, such instances were demonstrated by Palmer and other investigators long ago. It is but natural, therefore, that under such conditions the yellow color of the blood serum extracts will represent the resultant of different dye substances, whereas the chief aim of all these methods should be the determination of the real carotene content of the blood. The present method was devised to eliminate the above-mentioned errors. The carotenoids are precipitated completely from the blood serum by deproteination with alcohol. The dye is removed from the protein precipitate by repeated extraction with ether. After saponification of the lipoids and xanthophyll esters in the ether extract, the polyene hydrocarbons and xanthophyll dyes are separated from each other by dispersing them in a mixture of methyl alcohol and ether-petroleum-ether (“Entmischung”). The carotenes are contained in the upper layer, and may be determined in it colorimetrically.