URIC ACID 43 



The solution is cooled in running water, 1.5 c.c. of 10 per cent 

 sodium hydroxide are added, and the total creatinine is determined 

 as in the preformed creatinine determination using 1 mg. of 

 creatinine as a standard. The method has been found to give 

 good results in the presence of glucose and other sugars. 



Morris has suggested that in the case of diabetic urines the 

 total creatinine be determined after precipitation of the creatine 

 and creatinine with picric acid. The method is not recommended 

 as a regular procedure. 



URIC ACID 



Folin-Shaffer Method * 



Principle. The uric acid is precipitated as ammonium urate 

 by the addition of ammonia, the precipitate filtered off, washed 

 and titrated with potassium permanganate. A preliminary treat- 

 ment with an ammonium sulphate-uranium acetate solution is 

 for the purpose of removing interfering organic substances. The 

 method gives accurate results. 



Procedure. Introduce 100 c.c. of urine into an Erlenmeyer 

 flask, add 25 c.c. of the Folin-Shaffer reagent and after shaking 

 the flask to thoroughly mix the fluids allow the mixture to stand, 

 with or without further stirring, until the precipitate has settled 

 (five to ten minutes). Filter, transfer 100 c.c. of the filtrate to 

 a 200 c.c. Erlenmeyer flask, and 5 c.c. of concentrated ammonium 

 hydroxide and allow the mixture to stand for twenty-four hours. 

 Transfer the precipitated ammonium urate quantitatively to a 

 filter paper, using 10 per cent ammonium sulphate to remove the 

 final traces of the urate from the flask. Wash the precipitate 

 approximately free from chlorides by means of 10 per cent 

 ammonium sulphate solution, remove the paper from the funnel, 

 open it, and by means of hot water rinse the precipitate back 

 through the funnel into the flask in which the urate was originally 

 precipitated. The volume of fluid at this point should be about 

 100 c.c. Cool the solution to room temperature, add 15 c.c. of 

 concentrated sulphuric acid and titrate at once with N/20 

 potassium permanganate, K^M^Og, solution. The first tinge 

 of pink color which extends throughout the fluid after the addi- 

 1 Folin and Shaffer: Zeit. physiol. Chem., 1901, 32, 552. 



