SODIUM IN BLOOD 183 



to make a special standard as in method (6) for inorganic phos- 

 phates in plasma. 



SODIUM IN BLOOD 



Method of Kramer 1 



Principle. After ashing blood, serum or plasma, sodium is 

 precipitated by use of potassium pyroantimonate as Na2HoSb2O7. 

 6H20. The precipitate is collected in a crucible, dried and 

 weighed. 



Procedure. The ash of 1 or 2 c.c. of blood, serum, or plasma 

 obtained as described for the potassium method (see page 194) is 

 dissolved in water, in a platinum dish, using 0.5 c.c. of water for 

 each c.c. of serum, plasma, or blood. Solution may be aided by 

 the addition of a drop or two of N hydrochloric acid. The solution 

 is then made slightly alkaline with freshly prepared 10 per cent 

 KOH solution. Fifteen c.c. of the reagent and one-fifth of the 

 entire volume of absolute alcohol 2 are then added. Precipitation 

 occurs at once. The mixture is stirred, allowed to stand for at least 

 two hours (preferably over night), then transferred to the wet pad 

 of a weighed Gooch crucible as in the potassium method (see 

 page 194). It is then washed four or five times with 3 c.c. portions 

 of 30 per cent alcohol, dried at 110 C., cooled in a desiccator, and 

 weighed. 1 mg. of sodium yields 11.08 mg. of precipitate. All 

 reagents should be tested for the presence of sodium and ammonium 

 salts, especially the potassium hydroxide. A blank determination 

 should be done and the result subtracted from the Na determi- 

 nation in the sample. Most of the laboratory reagents will give a 

 slight precipitate with the potassium pyroantimonate reagent. 



Preparation of the Reagent. Potassium pyroantimonate 

 (J. T. Baker, c.p. analyzed chemicals), 2 gms. of the powder, is 

 added to 100 c.c. of boiling water in a 350 c.c. Pyrex flask and 

 heating continued until no more dissolves. It is then cooled 

 rapidly under the tap and 3 c.c. of 10 per cent KOH are added, 

 and the solution is stirred and filtered. The clear filtrate consti- 

 tutes the reagent. Although one may be able to precipitate sodium 



1 Kramer: Jour. Biol. Chem., 1920, 41, 271. 



2 The addition of too much alcohol will precipitate some of the reagent, 

 which is itself not very soluble and hence the results will be too high. 



