COLORIMETRIC METHOD FOR URIC ACID IN URINE 51 



Benedict and Hitchcock have examined the method of 

 Folin and Denis and have suggested a number of important 

 modifications. 



Procedure. Measure such an amount of urine as will contain 

 from 0.7 to 1.3 mg. of uric acid (2 to 4 c.c. is usually the correct 

 amount) into a centrifuge tube, dilute with water to about 5 c.c. 

 and add 15 to 20 drops of an ammoniacal silver magnesium solu- 

 tion. Mix the contents of the tube with a small stirring rod 

 and centrifuge the tube for one or two minutes. Pour off the 

 supernatant liquid, as completely as possible, by inverting the tube, 

 allowing it to drain a moment, and then touching the inside of the 

 lip of the tube with a towel or piece of filter paper. Add to the 

 residue in the tube 2 drops of 5 per cent solution of potassium 

 cyanide to dissolve the silver urate, stir the mixture thoroughly 

 with a thin rod, for half a minute, add a few drops (0.5 to 1.0 c.c.) 

 of water, and stir again. Two c.c. of the uric acid reagent are 

 added and the mixture stirred again, after which add 10 c.c. of 

 20 per cent sodium carbonate solution, transfer quantitatively to 

 a 50 c.c. flask, and at the end of about one-half minute, dilute to 

 mark. Compare this solution in the Duboscq colorimeter with 

 a simultaneously prepared solution obtained by treating 5 c.c. 

 of the standard uric acid solution, contained in a 50 c.c. flask, 

 with 2 drops of the potassium cyanide solution, 2 c.c. of the uric 

 acid reagent, 10 c.c. of 20 per cent sodium carbonate solution, 

 diluting to the mark at the end of about one-half minute. The 

 standard solution is best set at a height of 15 mm. in the colorim- 

 eter. 



Calculation. The reading of the standard divided by the 

 reading of the urine gives the number of milligrams of uric acid 

 in the amount of sample taken. 



COLORIMETRIC METHOD FOR DETERMINATION OF 

 URIC ACID IN URINE 



Folin and Wu 1 



Principle. Uric acid is precipitated as the urate by means of 

 silver lactate. Silver urate is then dissolved in an alkaline solu- 

 tion of sodium cyanide, and a uric acid reagent is then added. Thi 



and Wu; Jour. Biol. Chem., 1919, 38, 459, 



