194 METHODS FOR THE ANALYSIS OF BLOOD 



The sodium citrate used as an anticoagulant must also be tested 

 for the presence of potassium. 



POTASSIUM IN BLOOD 



Method of Kramer l 



Principle. Similar to that in the method of Clausen, page 191. 



Procedure. Blood is collected by puncture of the median 

 basilic, median cephalic, or external jugular vein. Whole blood 

 is collected directly into a weighed platinum crucible and rapidly 

 weighed. Plasma or serum may be collected under oil as in the 

 Van Slyke and Cullen determination of the CO2 combining power 

 of blood plasma. To obtain plasma, potassium-free ammonium 

 oxalate or oxalic acid may be used as anticoagulant. Although 

 ammonium salts react with sodium cobalti-nitrite, the ammonia 

 is completely volatilized during the ashing. To obtain serum, 

 the blood is collected under oil in a centrifuge tube and allowed to 

 remain in the ice box until the serum has separated. If the blood 

 is collected in this manner or in a clean, dry test-tube the danger 

 of hemolysis will be reduced to a minimum. 2 



Potassium Method 



One c.c. of blood, 3 to 5 c.c. of clear plasma, or an equal amount 

 of serum is dried in a platinum dish over the steam bath, then in 

 the incubator at 110 C. for about one-half hour. The dish or 

 crucible is then placed in a flat-bottomed quartz dish, 10 cm. in 

 diameter and 6 cm. deep, in the bottom of which are placed several 

 pieces of porcelain. The outer dish is then heated with the low 

 flame of a large Meker burner until fumes begin to come off. The 

 heating is continued until no more fumes are given off, when 

 the flame is turned on full until the charred material is immobile. 

 The large dish is then covered with a quartz plate and heating 

 continued until the material is completely ashed. 3 The platinum 



1 Kramer: Jour. Biol. Chem., 1920, 41, 263. 



2 Owing to the large amount of potassium present in corpuscles even a 

 moderate amount of hemolysis introduces considerable error. 



* The ashing often proceeds rapidly at first, then some residual carbon 

 is left which does not readily become oxidized. At this stage the ash is dis- 

 solved in a little concentrated hydrochloric acid, evaporated over the steam 



