POLYUNSATURATED FATTY ACIDS 791 



ber test for the analysis of fats evolved by Kaufmann/'^ it became possible 

 to determine the unsaturated fatty acids, both qualitatively and quanti- 

 tatively, with considerably more facility and precision than had hitherto 

 been the case. Thiocyanogen reacts quantitatively with monoethenoid 

 acids, but with only one unsaturated linkage of diethenoid acids, and with 

 only two of the three double bonds of triethenoid acids. By combining the 

 information obtained from the iodine value and from the thiocyanogen 

 number, Kaufmann^^"^* was able to determine the unsaturated fatty acid 

 composition of fatty acid mixtures. The procedure has been standardized 

 by Lambou and Dollear,^^'^" and it is now an official method of the Amer- 

 ican Oil Chemists' Society {Official and Tentative Methods). ^^ 



b. Solubility of Bromide Derivatives. The relative solubilities of the 

 bromides of the unsaturated acids were employed by Ault and Brown, ^^ 

 Shinowara and Brown, ''^ Brown and Frankel,®'* and \\Tiite and Brown^^ for 

 the estimation of polyunsaturated acids. However, because of substitution 

 reactions, the partial solubilities of the bromides, the mutual solubility 

 effects, the formation of isomers, which becomes more serious as unsatura- 

 tion increases, and also the differences in the solubilities of the isomers, this 

 procedure is much less satisfactory for quantitative assays than are some of 

 those recently proposed. 



c. Spectrophotometric Determination. Chemical and metabolic studies 

 on the pol^omsaturated acids received a tremendous impetus as a result of 

 the observation of IVIoore^^ that methylene-interrupted double bonds in 

 polyunsaturated fatty acids become partially conjugated upon prolonged 

 saponification. Since conjugated double bonds absorb ultraviolet light 

 of specific wave lengths, whereas methylene-interrupted double bonds do 

 not possess this property, this discovery suggested a procedure which 

 might be emplo3^ed as a quantitative assay for the qualitative and quanti- 

 tative determination of small amounts of polyunsaturated fats and oils. 



58 H. P. Kaufmann, Z. Untersnrh. Lebensm., 51, 15-27 (1926). 



" H. P. Kaufmann, Arch. Pharm., 1925 (Sonderdruck), 1-47; Chem. AbsL, 20, 3243 

 (1926). 



58 H. P. Kaufmann, Anah/st, 51, Abst., 157-158, 264-265 (1926). 



°« M. G. Lambou and F. G. Dollear, Oil & Soap, 22, 226-232 (1945). 



M M. G. Lambou and F. G. Dollear, Oil & Soap, 23, 97-101 (1946). 



81 American Oil Chemists' Societ}^, Official and Tentative Methods, 1946, Sect. C, Cd, 

 2-38, pp. 1-6. 



" W. C. Ault and J. B. Brown, .1. Biol. Chem., 107, 615-622 (1934). 



8' S. Y. Shinowara and J. B. Brown, J. Am. Chem. Soc, 60, 2734-2738 (1938). 



" J. B. Brown and J. PVankel, /. Am. Chem. Soc, 60, 54-56 (1938). 



8» M. F. White and J. B. Brown, /. Am. Oil Chemists' Soc, 26, 385-388 (1949). 



«6T. Moore, Biochem. J., 31, 138-154 (1937). 



