CREATINE AND CREATININE 101 



prevent the growth of bacteria or moulds in the solution. Five 

 c.c. of this solution contains exactly 1 mg. of uric acid. 



CREATINE AND CREATININE 



Methods of Folin 1 



Preformed Creatinine. Measure 10 c.c. of blood into a 50 c.c. 

 volumetric flask or, better, into a 50 c.c. shaking cylinder which 

 can be closed with a glass stopper. Fill to the 50 c.c. mark with 

 saturated picric acid solution and shake a few times. Add about 

 1 gm. of dry picric acid to the mixture and shake for five minutes. 

 Transfer the mixture to centrifuge tubes, throw down the sediment 

 and precipitate and pour the supernatant liquid through a filter. 

 This is the most economical process where but little blood is 

 available. If desired, however, double quantities of blood and 

 reagents may be taken and filtration carried out without prelimi- 

 nary centrifugation. This process removes the protein materials 

 and leaves the creatine and creatinine in the filtrate which is a 

 saturated picric acid solution. The preformed creatinine is then 

 determined colorimetrically. For this purpose a standard solution 

 of creatinine for comparison is necessary. This standard solution 

 should contain 0.2 mg. of creatinine in 100 c.c. of saturated picric 

 acid solution. 



Take 20 c.c. portions each of the filtrate and of the standard 

 solution. To each solution then add exactly 1 c.c. of 10 per cent 

 NaOH from a burette. (If the blood filtrate become turbid on 

 addition of alkali it must be centrifuged or filtered.) Allow to 

 stand for ten minutes and compare the colors directly in the 

 colorimeter without further dilution. The standard creatinine 

 solution may be set advantageously at 20 mm., although this is 

 not necessary. 



Calculation. Since the blood was diluted five times in the 

 precipitation procedure and as the standard for comparison con- 

 tains 0.2 mg. of creatinine per 100 c.c., it is merely necessary to 

 divide the reading of the standard by the unknown to obtain 

 without further calculation the number of milligrams of creatinine 

 in 100 c.c. of blood. 



1 Folin: Jour. Biol. Chem., 1914, 17, 475. 



