DIRECT DETERMINATION OF SODIUM IN SERUM 189 



DIRECT DETERMINATION OF SODIUM IN SERUM 



Method of Kramer and Tisdall * 



Principle. Serum is treated directly with the potassium 

 pyroantimonate reagent and alcohol. The precipitate is collected 

 in a weighed Gooch crucible, dried, and weighed. 



Procedure. Two c.c. of serum are transferred to a platinum 

 dish. To these are added 10 c.c. of the potassium pyroantimonate 

 reagent followed by 3 c.c. of 95 per cent alcohol. The alcohol 

 should be added drop by drop and the specimen stirred with a 

 rubber-tipped rod. After standing forty-five minutes, the pre- 

 cipitate is transferred to a weighed Gooch crucible and washed 

 with 8 to 12 c.c. of 30 per cent alcohol. The crucible is dried at 

 110 C. for one hour, 2 cooled in a desiccator for thirty minutes 

 and weighed. The weight of the precipitate divided by 11.08 

 equals the number of mg. of sodium present in the sample. 



Preparation of the Potassium Pyroantimonate Reagent 



Five hundred c.c. of distilled water are heated to boiling in a 

 Pyrex flask and approximately 10 gms. of potassium pyroanti- 

 monate (J. T. Baker) are added. The boiling is continued from 

 three to five minutes, the flask immediately cooled under running 

 water, and when the contents are cold 15 c.c. of 10 per cent KOH 

 (alcohol- washed) are added. The reagent is then filtered through 

 ash-free filter paper into a paraffined bottle. Frequently some of 

 the undissolved potassium pyroantimonate will pass through even 

 the best filter paper. If the reagent is allowed to stand twenty- 

 four hours after filtering, all the undissolved potassium pyroanti- 

 monate will settle to the bottom. The supernatant fluid is then 

 clear and may be used as long as it remains so. The reagent 

 keeps perfectly well at room temperature for at least one month. 

 10 c.c. of this reagent will precipitate 11 mg. of sodium. The 

 10 per cent KOH should also be kept in a paraffined bottle. 



Before the reagent is used for the first time, it should be tested 

 for the presence of sodium and also the fact ascertained that none 



1 Kramer and Tisdall: Jour. Biol. Chem., 1921, 46, 467. 



2 The crucible is placed in the oven the temperature of which is gradually 

 raised to 110 C. 



