Determination of Calcium in Blood and Plasma. 137 



and immediately centrifuged. After removal of the wash water 

 the precipitate is dissolved in 5 c.c. of approximately normal 

 sulfuric acid and, after heating in a water bath to 75 0 C, the 

 contents are titrated with 0.01 normal potassium permanganate. 

 (After precipitation of the calcium the method follows, with minor 

 modifications, that described by Halverson and Bergeim. 2 



Plasma. — Citrated plasma (5 c.c. in a 50 c.c. centrifuge tube) 

 is diluted with an equal volume (5 c.c.) of one per cent, ammonium 

 chloride and 10 c.c. of one per cent, ammonium oxalate are slowly 

 added. After standing 16 hours the precipitate is centrifuged, 

 washed and titrated as in the procedure for blood. 



The method has been checked by: 



1 . The determination of known amounts of calcium in solutions 

 having approximately the same mixture of salts as is found in the 

 blood. 



2. The ashing of whole blood and plasma in platinum dishes 

 and precipitation of the calcium by a modification of McCrudden's 3 

 method. 



3. The addition of known amounts of calcium to plasma and 

 recovery by the above method. 



The advantages of this method are: 



1. The small amount of sample necessary, 5 c.c. blood and 3 

 to 5 c.c. of plasma. 



2. The few reagents necessary and the relative ease of preparing 

 them free from calcium. 



3. The precipitation of the calcium in the presence of the 

 proteins. Methods 2> 4 now in common use require either ashing 

 or removal of the proteins by precipitation, operations which 

 greatly add to the chances for mechanical losses. 



The accuracy of this method lies between five and seven per 

 cent. 



2 Halverson, J. O., and Bergheim, O. J. Biol. Chem., 1917, 32, p. 159. 



3 McCrudden, F. H. J. Biol. Chem., 1909-10, 7, p. 83; /. Biol. Chem., 191 1- 

 12, 10, p. 187. 



4 Lamers, A. J. M. Z. Z. Gebiirts. u. Gynak., 1912, 71, p. 393. 

 Lyman, H. J. Biol. Chem., 1917, 29, p. 169. 



Marriott, W. McK., and Howland, J. J. Biol. Chem., 1917, 32, p. 233. 

 Jansen, W. H. Z. physiol. Chem., 1917-18, 101, p. 176. 

 Heubner, W., and Rona, P. Biochem. Z., 1919, 93, p. 187. 



/ 



