792 Xni. ESSENTIAL FATTY ACIDS 



Mitchell, Kraybill, and Zscheile," in 1943, proposed the first standardized 

 empirical procedure for ascertaining the saturated, and mono-, di-, and 

 triethenoid acids by the use of alkali isomerization and spectrophotometric 

 measurements, combined with the determination of the iodine values. In 

 1944 the use of this procedure was extended to tetraenoic acids by Beadle 

 and Kraybill,^^ who reported the extinction coefficient for arachidonic 

 acid. 



The alkali-isomerization method for the determination of the polyun- 

 saturated acids now generally in use is essentially that described by Brice 

 and co-workers,^^ who employed new standards for extinction coefficients. 

 These standards were prepared from "natural" acids by chromatographic 

 procedures, rather than those used by Brice and Swain^" and by Brice el 

 al.,''^ which included bromination-debromination technics. 



The Spectroscopy Committee of the American Oil Chemists' Society^'- 

 has developed a modification of the above method in which ethylene glycol 

 is used for the saponification medium, and in which nitrogen gas is employed 

 to prevent oxidation. With some modifications, the same procedure has 

 been accepted by the American Oil Chemists' Society as a tentative method. 



Although the AOCS method can be carried out with 50 to 100 mg. of 

 sample, micromethods have been devised for use when limited amounts of 

 fat are available. Thus, Herb and Biemenschneider^^ devised a procedure 

 which requires only 1 to 10 mg. of fat, and microprocedures have been 

 devised for the determination of polyunsaturated acids in blood by O'Con- 

 nell et al.,'^* Wiese and Hansen.''^ 



d. Resume of Method for the Analysis of Polyunsaturated Acids. The 

 spectrophotometric method involving the alkali isomerization of poly- 

 unsaturated fatty acids is the most accurate and sensitive technic for the 

 determination of these several unsaturated acids. This procedure, how- 

 ever, does have some limitations. Thus, in the determination of linoleic 



"J. H. Mitchell, Jr., H. R. Kraybill, and F. P. Zscheile, Ind. Eng. Chem., Anal. Ed., 

 i5, 1-3(1943). 



«8 B. W. Beadle and H. R. Kraybill, /. Am. Chem. Soc, 66, 1232 (1944). 



89 B. A. Brice, M. L. Swain, S. F. Herb, P. L. Nichols, Jr., and R. W. Rieraenschneider, 

 J. Am. Oil Chemists' Soc, 29, 279-287 (1952). 



'» B. A. Brice and M. L. Swain, /. Opt. Soc. Amer., 35, 532-544 (1945). 



71 B. A. Brice, M. L. Swain, B. B. Schaeffer, and W. C. Ault, Oil & Soap, 22, 219-224 

 (1945). 



''"'■ R. C. Stillman, Report of the Spectroscopy Committee, J . Am. Oil Chemists' Soc, 

 ^6^,399-404(1949). 



" S. F. Herb and R. W. Riemenschneider, Anal. Chem., 25, 953-955 (1953). 



7* P. W. O'Connell, E. Lipscomb, and B. F. Daubert, Arch. Biochem. Biophys., 36, 

 304-310(1952). 



'5 H. F. Wiese and A. E. Hansen, /. Biol. Chem., 202, 417-423 (1952). 



