562 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Estimation of Creatinine. 



This method is the same as described on p. 555, but smaller quantities- 

 are used ; a creatinine standard is used instead of bichromate. 



i c.c. of urine + 20 c.c. of picric acid solution + 1*5 c.c. of 10 per cent, 

 caustic soda from a burette are placed in a 100 c.c. measuring flask. At the 

 same time i c.c. of standard creatinine solution is treated in the same way. 



After 10 minutes the flasks are filled to the mark with water, the contents 

 are mixed and the colour comparison is made. The standard is set at 10, 

 15, or 20. 



standard 



i = merm. creatinine in i c.c. urine. 



unknown 



The determination must be repeated with more or less urine if the reading 

 is less than f or more than i times that of the standard. 



The creatinine standard should not be diluted so that 5 c.c. of it can be 

 measured out instead of i c.c., and 5 c.c. of the urine should not be diluted 

 to 500 c.c., but 5 c.c. of urine diluted 4 times (i : 4) may be used, or 5 or 

 10 c.c. of standard may be used. In the latter case 5 c.c. of alkali must be 

 added. If the urine is so dilute that 5 c.c. are necessary, the standard should 

 also be diluted to 5 c.c. with water before adding the picric acid and soda. 



Standards of o - 5 and 0*2 mgm. of creatinine may be used. Other 

 creatinine solutions may be similarly estimated. 



Estimation of Creatine. 



The conversion of creatine into creatinine in small quantities is effected 

 by heating with picric acid. 



Enough urine to give 0-7-1-5 mgm. creatinine is measured into a 200 

 c.c. weighed conical Jena glass flask, 20 c.c. of picric acid and 130 c.c. of 

 water are added. The solution is gently boiled over a micro-burner for about 

 one hour, a few small pebbles being introduced to promote even boiling ; the 

 heat is increased so that it evaporates to rather less than 20 c.c. The flask is 

 placed on the balance and water is added so that the contents weigh 20-25 gm. 

 The solution is cooled and 1*5 c.c. of 10 per cent, sodium hydroxide are 

 added. At the same time a standard i mgm. of creatinine is prepared. 



The conversion can be effected in an autoclave by heating with the 

 picric acid for half an hour at 120, cooling and adding the soda as above. 



