790 XIII. ESSENTIAL FATTY ACIDS 



The saturated acids do not react with 2,4-dinitrobenzenesulfenyl chloride, 

 whereas the derivatives of the unsaturated acids were found to be separable 

 into well-defined bands on MgS04 columns. They could be recovered as 

 individual compounds in an eluate of benzene/ether (95/5), with yields 

 above 95% in each case (oleic, linoleic, and linolenic acids). Zechmeister^^ 

 reviewed the subject of partition chromatography, and Holman^'^ has 

 more recently discussed the subject of separation of fatty acids from a 

 somewhat broader viewpoint. 



In 1955 Howton^^ reported that the bromine derivatives of the methyl 

 esters of polyunsaturated acids are "easily and cleanly separated by gradi- 

 ent elution from alumina chromatographic columns." 



Crombie, et al.}^ approached this problem by reversed-phase chromatog- 

 raphy. Alkaline permanganate oxidation was used to separate the satu- 

 rated from the unsaturated acids, which were eluted at equal rates. 



Inouye, Noda, and Hirayama^^ reported a reversed-phase paper chroma- 

 tographic procedure for the determination of mercuric acetate addition 

 compounds of unsaturated fatty acid esters. Silk and Hahn^^ have devised 

 a method for the analysis of pilchard oil based upon preliminaiy separation 

 of the unsaturated acids by the lithium soap-acetone technic, urea complex 

 fractionation, and molecular distillation. The unsaturated acids were 

 further resolved by reversed-phase partition chromatography, and the 

 chain length by complete hydrogenation followed by reversed-phase parti- 

 tion chromatography. 



{3) Chemical and Physical Methods for the Analysis of Polyunsaturated Acids 



The qualitative and quantitative determinations of the polyunsaturated 

 acids have posed exceedingly refractory problems, and they have only 

 recently been partially resolved. The earlier methods were tedious, and 

 of such uncertain interpretation that they were of little value. Frequently, 

 they were resolved by the very unsatisfactory expedient of measuring 

 changes of iodine value. It is obvious that only the simplest generaliza- 

 tions can be arrived at by such procedures. 



a. Thiocyanogen Number. With the advent of the thiocyanogen num- 



^' L. Zechmeister, Progress in Chromatography, 1938-1.947, Chapman & Hall, TiOndon, 

 1950. 



"» R. T. Holman, Progr. Chem. Fats and Other Lipids, 1, 104-126 (1953). 



" D. R. Howton, Science, 121, 704-706 (1955). 



" W. M. L. Crombie, R. Comber, and S. G. Boatman, Biochem. J., 69, 309-316 (1955). 



"Y. Inoiive, M. Noda, and O. Hirayama, ./. Am. Oil Chemists' Soc, 32, 132-135 

 (1955). 



" M. H. Silk and H. H. Hahn, Biochem. J., 57, 577-582 (1954). 



