Abstract
Deficiencies in Purification of Lipids by Petrol Ether. Resolution in petrol ether has been a classical procedure for analytical purification of extracted fats. Thus the blood fats extracted with Bloor's 1 efficient alcohol-ether mixture are, for certain analyses, dried and purified by resolution in petrol ether. 1 , 2 , 3 The non-lipid extractives, such as urea, glucose, amino acids, and inorganic salts, dissolve in varying amounts in the alcohol-ether, but they do not by themselves dissolve in petrol ether.
It has been recognized, however, that the petrol ether solutions show higher N:P ratios than could be expected from any of the known phosphatides. Several attempts have been made to identify the extra nitrogen. 4 , 5 , 6
The present writers have been able to identify most of it as urea, determinable with urease and other urea regeants. Urea by itself is insoluble in petrol ether, but dissolves measurably in it when the blood lipids are present. Measurable amounts of amino acids, determinable by the specific amino acid carboxyl method of Van Slyke and Dillon, 7 are also present.
On the other hand, petrol ether fails to redissolve the phosphatides completely. A fraction of them remains in the undissolved residue. It is slight in normal plasmas, but in certain pathological ones it may represent 40% of the phosphatides. It has the following properties suggestive of sphingomyelin: soluble in alcohol, insoluble in petrol ether, N/P ratio of 2, C/P ratio of about 45. All the other lipids seem to be completely redissolved by the petrol ether.
Proposed Extraction. The proteins and lipids are precipitated together by colloidal iron, and the water-soluble extractives are washed away. The lipids are then extracted by stirring up the wet precipitate with alcohol and ether.
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