506 THE TOCOPHEROLS 



The protective effect is believed to be in the tissues, since the vitamin A 

 of the unsupplemented cod hver oil diet did not diminish during storage 

 of the food or under conditions resembling those in the alimentary tract. 

 Of particular interest was the observation that methylene blue could par- 

 tially replace tocopherol in preventing the sterility of female rats on vita- 

 min E-deficient diets. Vitamin E is thus a biological antioxidant, or it can 

 maintain the integrity of certain enzymatic redox sj'^stems in which methy- 

 lene blue can replace the vitamin. 



( 



V. Estimation 



HENRY A. MATTILL 



A. QUANTIATIVE DETERMINATION I 



Quantitative methods for the determination of tocopherols include chemi- 

 cal, physical, and biological procedures. All are described and critically 

 evaluated in two recent volumes. ^ 



1. Chemical Assay 



The chemical methods are based largely on the assay of oxidation prod- 

 ucts. The most complete oxidation is that obtained in the Furter-Meyer 

 method with nitric acid, the color of the chroman-5 , 6-quinone being de- 

 termined spectrophotometrically or colorimetrically. Volumetric titration 

 methods have been developed with eerie sulfate- and lead tetraacetate.' 

 By means of the latter, almost pure tocopherylquinone can be prepared. 



A procedure was also devised for the simultaneous determination of to- 

 copherol, tocopherylquinone, and vitamin K,^- ^ involving oxidation to 

 quinone, reduction to the respective hydroquinones, and the use of 2,6- 

 dichloroindophenol. Immediate diminution of the blue color is a measure 

 of vitamin K; subsequent slower reduction is due to tocopherylhydroqui- 

 none. 



The most versatile and commonly used method is based on the oxidation 

 of tocopherol to tocopherylquinone by ferric chloride in the presence of 

 Q:,a:-dipyridyl, the resultant ferrous chloride being measured by the red 

 color produced.^ The blue color produced on the addition of potassium fer- 



1 P. Gyorgy, Vitamin Methods. Academic Press, New York, 1950, 1951. 



2E. Schulek and P. Rozsa, Z. anal. Chem. 126, 253 (1943). 



» A. Issidorides, J. Am. Chem. Soc. 73, 5146 (1951). 



' J. V. Scudi and R. P. Buhs, J. Biol. Chevi. 146, 1 (1942). 



fi N. R. Trenner and F. A. Bacher, J. Biol. Chem. 137, 745 (1941). 



6 A. Emmerie and C. Engel, Rec. irav. chim. 57, 1351 (1938). 



