POLYUNSATURATED FATTY ACIDS 789 



saturated fatty acids (C2 to Cs) by the additional precaution of buffering the 

 silica gel tube. Peterson and Johnson^'* reported that the even-chain acids 

 from C2 to Cio, and also forniic acid, could be separated by employing ben- 

 zene-a(|ueous sulfuric acid in Celite-packed tubes. This procedure is the 

 first which has found application in the fractionation of unsaturated fatty 

 acids. ^* Oleic and linoleic acids could be effectively separated by this method 

 to a degree not possible b}^ other fractionation methods. Abu-Xasr and 

 Holman^-^ isolated docosahexaenoic acid from cod-li\'er oil by adsorption on 

 charcoal in a modified Tiselius-Claesson apparatus, as described by Hol- 

 man and Hagdahl.*^ Abu-Xasr and Holman*^ also reported the prepara- 

 tion of eicosapentaenoic acid of 91% purity by the preliminary concentra- 

 tion of the saturated acid on silicic acid, followed by its adsorption on char- 

 coal in the modified Tiselius-Claesson apparatus. T\Tien silicic acid was 

 used as the adsorbent and a petroleum ether-chloroform mixture as the 

 eluant, these workers succeeded in preparing almost pure ethyl docosapen- 

 taenoate. 



Some of the highly purified esters of the pol.yimsaturated acids were pre- 

 pared by the workers at the Easten Regional Research Laboratories of the 

 United States Department of Agriculture, by adsorption on silicic acid 

 followed by fractionation. The products prepared included the methyl 

 esters of natural linoleic and linolenic acids, ''^ almost pure methyl arachido- 

 nate,^^ methyl eicosapentaenoate and methyl docosapentaenoate.^^ In 

 general, the procedure involved the separation of oleic acid from the mix- 

 ture by crystallization from acetone at a low temperature, the subsequent 

 removal of the nonsaponifiable matter, the preparation of the methyl esters 

 of the fatty acids, followed b}- their adsorption on silicic acid. Elution was 

 carried out with petroleum ether containing 0.25% ethyl ether. 



Simmons and Quackenbush^" employed a combined technic of chromato- 

 graphic separation and elution of 2,4-dinitrobenzenesulfenyl chloride deriv- 

 atives of unsaturated acids as a new ''isolation" method of analysis. 



« M. H. Peterson and M. S. Johnson, J. Biol. Chem., 174, 775-789 (1948). 



** C. L. Reinhold and H. J. Dutton, ./. A771. Oil Chemists' Soc, 25, 117-120, 120-124 

 (1948). 



« A. M. Abu-Xasr and R. T. Holman, J. Am. Oil Chemists' Soc, 31, 41-45 (1954). 



« R. T. Holman and L. Hagdahl, Anal. Chem., 23, 794-797 (1951). 



■" R. W. Riemenschneider, S. F. Herb, and P. L. Nichols, Jr., /. .4//(. Oil Chemists' Soc, 

 371-374(1949). 



*^ S. F. Herb, R. W. Riemenschneider, and J. Donaldson, J. Am. Oil Chemists' Soc, 28, 

 55-58 (1951). 



■*' S. F. Herb, L. P. Witnauer, and R. W. Riemenschneider, /. Am. Oil Chemists' Soc, 

 ^5, 505-507(1951). 



^ R. O. Simmons and F. W. Quackenbush, J. Am. Oil Chemists' Soc, SO, 614-616 

 (1953). 



