V O L U M E 21, NO. 8, A U G U S T 1 9 4 9
1011
only for the determination of riboflavin but also for the determination of pyridoxine and nicotinic acid by the dynamic method. 4CKNOWLEDG.MENT
The authors wish to thank U. Miura, R. Oda, and M. Nishio of Kyoto University for valuahle advice and assistance in this investigation. LITERATURE CITED
1\11 Brown, E. B., Bina, A. F.. and Thomas. T. &JI..Biol. . Chem , 158,455 (1945).
(2) Conner, R. T., and Straub, G. J., IKD.ENG.CHEY.,ASAL. ED., 13,385 (1941). (3) Euler, H. von, and Adler, E., Z . physiol. Chem., 223, 105 (1934). (4) Fujiwara, M., and Kitamura, S., J a p a n . J . Hug., 2, 12 (1948). ( 5 ) Hennessy, D. J., IND.Esc;. CHEM.,ASAL. ED.,13, 216 (1941). ( 6 ) Herr, D. S., I n d . Eng. Chem., 37, 631 (1945). (7) Kharit, 9.Yu., and Khaustov, N. W.,Biochem. J . , 29, 34 (1935) (8) Koshara, IT., 2. physiol. Chem., 232, 101 (1935). (9) Ode, R., Shirnizu, H., and Nakayama, Y . , Chemistry of High Polymer, to be published. (10) Supplee, G. C., Ansbacher, S., Flanigan. G. E., and Hanfod. Z . M., J . Dairy Sei., 19, 215 (1936). K E C E I V F . ~September 22. 1948.
Volumetric Determination of Small Amounts of Iron Chromous Chloride as Reducing Agent WILLIAM D. COOKE, F R E D HAZEL, AND WALLACE RZ.
3ICNABB
University of Pennsylvania, Philadelphia, Pa. communication showed that chromous chloride Lamalgam 4 PREVIOUS gave excellent results when employed with liquid zinc as a reducing agent for ferric ions (f and that its favor),
Table I. Determination of Iron Fe Taken,
Fe Found,
hlg.
A1g.
%
9,047
9.022 9.013 9.026 9.018 9.020
-0 3
3.619
3.632 3.626 3.615 3.613 Mean 3 . 6 2 1
f0.3 +0.2 -0.1 -0.2
1.810
-0.3 f0.6 0 -0.1
Mean
1.805 1.820 1.810 1.808 1.811
+0.8
Mean
0.730 0,724 0.717 0.713 0.721
0,362
0.358 0.357 0.357 0.363 Mean 0 . 3 5 9
-1.1 -1.4 -1.4 $0.3
0.302
0.301 0.295 0.301 0.294 0.298
-0.3 -2.3 -0.3 -2.6
0.119 0.120 0.119
-0.8
Mean
0.724
Mean 0.120
0.120
Mean 0.120
Error, -0.4 -0.2 -0.3
0 -1.0 -1.5
0
-0.8 0
able application as a reducing agent depended upon the fact that the excess chromous ion is oxidized by atmospheric oxygen with no appreciable oxidation of the iron under the conditions of the experiment. Phenosafranine, a low potential redox indicator, was used to follow the reactions. Chromous chloride alone is a satisfactory reducing agent for small amounts of iron. The method can be applied to solutions containing 0.1 mg. to 10 mg. of iron satisfactorily; viith larger amounts of iron, the green color of the chromic ions interferes. A single determination can be carried out in 2 to 3 minutes n-ithout the use of an inert atmosphere. The reagents were used a t the concentrations shown in the following procedure and viere prepared by methods already described ( 1 ) . The average error for twelve determinations using between 1 and 10 mg. of iron was 0.250J0. The average error was 0.9% in sixteen determinations using less than 1 mg. of iron. Five to 25 ml. of ferric iron solution containing 0.1 to 9 mg. of iron are acidified with either sulfuric or hydrochloric acid, and 2 or 3 drops of 0.017, phenosafranine indicator are added. Chromous chloride solution is then added dropwise until the pink color of the indicator disappears and the solution becomes a light clear green. The solution is swirled until the pink color reappears (this color is not the same as the original pink because of the added chromic ions). A few drops of phosphoric acid and 0.05 to 0.1 ml. of a 0.16% diphenylamine sulfonate solution are added and the ferrous iron is titrated with a solution of potassium dichromate. A 0.007 i Y solution of potassium dichromate is used for amounts of iron greater than 1 mg. A 0.003 S solution is used for less than 1 mg. The end point is a purple color which is easily detected over the light pink or violet color of the solution. A correction of 0.05 ml. of 0.01 ?; potassium dichromate is subtracted for each 0.1 ml. of indicator used in the titration. In the titration of less than 1 mg. a solution of the oxidized form of the diphenylamine sulfonate was used and gave a blank of 0.01 ml. of 0.01 iz’ potassium dichromate for each 0.1 ml. of indicator. LITERATURE CITED
(1) Cooke, Hazel, and McNabb, ANAL.CHEM.,21, 643 (1949). RECEIVED November 19, 1948. Presented before the Meeting-in-Miniature. Philadelphia Section. AYERICAX CHEMICAL SOCIETY, January 20, 1949.
