V. ESTIMATION 507 



ricj'anide can also be used." Interfering substances such as vitamin A and 

 other materials readily oxidized under the conditions must be removed by 

 various means,^ such as selective adsorption on Floridin XS^ or clay/" treat- 

 ment with concentrated sulfuric acid," hydrogenation/- or high-vacuum'^ 

 or molecular distillation" of the tocopherols from extracts. Or the deter- 

 mination can be made before and after acetylation, the difference being a 

 measure of tocopherol.'" 



With minor modifications, tliis method has had wide use; typical ex- 

 amples are cited of its application to oils,'^' " foodstuffs,'^ plant'^ and ani- 

 mal-""-^ tissues and serum.-""*' 



In the presence of fats, the amount of color produced is greatly depressed, 

 for reasons as yet unknowTi;*- the effect varies \\-ith the nature and concen- 

 tration of the fat, and the interference is, of course, avoidable by prelimi- 

 nary separation of the unsaponifiable portion, with due care to prevent 

 loss due to the high temperature of saponification. 



The less sensitive potentiometric method by which tocopherol is oxidized 

 to tocopherylquinone with gold chloride** is subject to the same interfer- 



^ P. Meunier and A. Vinet, Compt. rend. 211, 611 (1940); An?i. chim. anal, et chim. 



appl. 23, 145 (1941). 

 8 J. G. Baxter, Biol. Symposia 12, 484^507 (1947). 

 ' A. Emmerie and C. Engel, Rec. trav. chim. 58, 283 (1939). 



10 P. Meunier and A. Vinet, Bull. soc. chim. biol. 24, 365 (1942). 



11 W. E. Parker and W. D. McFarlane, Can. J. Research, B18, 405 (1940). 



12 M. L. Quaife and R. Beihler, J. Biol. Chem. 159, 663 (1945). 



" J. Glavind, H. Heslet, and I. Prange, Z. Vitaminforsch. 13, 266 (1943). 

 » M. L. Quaife and P. L. Harris, Ind. Eng. Chem. Anal. Ed. 18, 707 (1946). 



15 A. Emmerie and C. Engel, Z. Vitaminforsch. 13, 259 (1943). 



16 A. Emmerie, Rec. trav. chim. 59, 246 (1940); 60, 104 (1941). 

 " J. Tosic and T. Moore, Biochem. J. 39, 498 (1945). 



18 M. L. Quaife and P. L. Harris, Anal. Chem. 20, 1221 (1948). 



19 M. E. Wall and E. G. Kelley, Ind. Eng. Chem. Anal. Ed. 18, 198 (1946). 



20 M. L. Quaife and M. Y. Dju, J. Biol. Chem. 180, 263 (1949). 



21 H. B. Devlin and H. A. Mattill, /. Biol. Chem. 146, 123 (1942). 



22 L. R. Hines and H. A. IMattill, /. Biol. Chem. 149, 549 (1943). 



23 H. Kaunitz and J. J. Beaver, J. Biol. Chem. 166, 205 (1946). 



2< M. L. Quaife, W. J. Swanson, M. Y. Dju, and P. L. Harris, Ann. N. Y. Acad. Sci. 



52, 300 (1940). 

 2* A. Emmerie and C. Engel, Rec. trav. chim. 58, 895 (1939). 



26 A. Emmerie, Rec. trav. chim. 61, 305 (1942). 



27 G. G. Mayer and H. Sobotka, J. Biol. Chem. 143, 695 (1942). 



28 A. S. Miuot, J. Lab. Clin. Med. 29, 772 (1944). 



29 M. L. Quaife and P. L. Harris, /. Biol. Chem. 156, 499 (1944). 



"> M. L. Quaife, X. S. Scrimshaw, and O. H. Lowry, /. Biol. Chem. 180, 1229 (1949). 

 " M. Farber, A. T. Milhorat, and H. Rosenkrantz, Proc. Soc. Exptl. Biol. Med. 



79, 225 (1952). 

 « H. Kaunitz and J. J. Beaver, /. Biol. Chem. 156, 653, 661 (1944). 



