292 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Estimation of Uric Acid. 



A. Uric acid is readily oxidised by potassium permanganate and 

 converted into allantoine and other products of its oxidation. Use 

 is made of this reaction for its estimation. From solutions, such as 

 urine, in which other organic substances are present, the uric acid 

 must be precipitated before it can be estimated (p. 554). 



O5N potassium permanganate (1-581 gm. per litre) is commonly 

 used in the process. 



The permanganate solution is placed in^a burette with a glass tap 

 (rubber cannot be used as it is attacked by permanganate). The level 

 of the liquid in the burette is most conveniently read by holding a 

 lighted match behind it. 



100 c.c. of a solution of uric acid, or the same volume of a solution 

 containing a weighed quantity of uric acid, or solid urate ('5-1 gm. 

 dissolved in water containing soda and diluted to i litre), are placed 

 in a flask or beaker, 20 c.c. of concentrated sulphuric acid are added, 

 the solutions are well mixed and the permanganate is run in whilst 

 the solution is hot. 



At first every drop of permanganate is decolorised before it 

 diffuses through the liquid. The end point is reached as soon as a 

 drop produces a pink flush throughout the liquid. This pink colour 

 disappears on standing ; another drop of permanganate will again 

 produce a pink flush. This can be continued for some time so that 

 the first pink flush must be carefully looked for. 

 Calculation : 



I c.c. of 'O5N KMnO 4 corresponds to 0x30375 gm. uric acid. 

 . . x c.c. correspond to x x '00375 gm. in 100 c.c. solution. 



B. By means of the colour reaction with phosphotungstic acid Folin has 

 shown that quantities of uric acid amounting to i mg. in i c.c. can be ac- 

 curately estimated. This method is particularly uselul for estimating uric 

 acid in blood and can be used for estimating uric acid in small quantities of 

 urine (pp. 565, 580). 



