46 METHODS FOR THE ANALYSIS OF URINE 



This proportion may be used for the calculation no matter 

 what volume of urine (5, 10, or 15 c.c.) is used in the determina- 

 tion. The 10 represents 10 mg. of creatinine which gives a 

 color equal to 3.1 mm., whether dissolved in 5, 10, or 15 c.c. 

 of fluid. 



Calculate the quantity of creatinine in the twenty-four hour 

 urine specimen. 



Use of Pure Creatinine Standards 



Instead of using as a standard a potassium dichromate solu- 

 tion as above indicated, a solution of pure creatinine is to be 

 recommended. By using this certain arbitrary factors are 

 eliminated and the method becomes of more general applicability. 

 The standard need not be set at a definite mark as is necessary 

 in the case of dichromate and temperature and time have less 

 influence on the accuracy of the results. A stock solution of pure 

 creatinine is made by dissolving 1 gm. of the substance in sufficient 

 N/10 HC1 to make a liter. This solution contains 1 mg. of 

 creatinine per cubic centimeter. In carrying out the deter- 

 mination treat 10 c.c. of the stock solution in the same way and 

 at the same time as the 10 c.c. sample of urine. Compare in the 

 colorimeter. The calculation is simple. The reading of the 

 standard divided by the reading of the urine gives directly the 

 number of milligrams of creatinine per cubic centimeter of urine. 



CREATININE 



Folin's Microchemical Modification 1 



Principle. The principle is the same as that of the original 

 colorimetric method. This procedure is to be recommended 

 particularly where only small amounts of material are available. 



Procedure. One c.c. of the standard creatinine (see above) 

 solution (1 mg. per c.c.) is measured into a 100 c.c. volumetric 

 flask and 1 c.c. of urine into another; 20 c.c. of saturated picric 

 acid solution (measured with a cylinder) are added to each and 

 then 1.5 c.c. of a 10 per cent solution of sodium hydroxide. At 

 the end of ten minutes the flasks are filled up to the mark with 



Jour. Biol. Chem., 1914, 17, 469. 



