ANALYSIS OF URINE 555 



Creatinine. 



Creatinine is estimated by Folin's adaptation of the Jaff colour re- 

 action of creatinine with picric acid and caustic soda (p. 171). Folin 

 found that a layer 8 mm. deep of ^N potassium bichromate solution 

 had the same colour as a layer 8 'I mm. deep of a solution prepared 

 from 10 mgm. of pure creatinine, picric acid and caustic soda. By 

 comparing the colour of an unknown solution with that of bichromate 

 in a Duboscq colorimeter, the amount of creatinine can be determined 

 as the colours are directly proportional. 



Procedure. 



10 c.c. of urine are measured with a pipette into a 500 c.c. measur- 

 ing flask, 1 5 c.c. of saturated picric acid solution and exactly 5 c.c. of 

 I o per cent, sodium hydroxide are added. The mixture is allowed to 

 stand for 5-7 minutes and diluted to 500 c.c. with water. The colour 

 of this solution is compared with that of ^N bichromate in a colorimeter. 



The bichromate solution is placed in one of the cups of the colori- 

 meter and the depth through which the colour is viewed is adjusted to 

 & mm. by means of the screw and the vernier on the scale. The un- 

 known is placed in the other cup. The comparison is made by altering 

 the depth by means of the screw on this side of the instrument until the 

 colours match. Readings should be taken by matching from too light 

 and from too dark and the mean of 6-IO readings should be taken. 



The result is calculated as follows : 



Suppose 9*5 mm. of the unknown match 8 mm. of the bichromate, 

 then since 8'i mm. of the bichromate corresponds to 10 mgm. of 

 creatinine and since the readings are proportional, 



o ., 



10 x -7-, or 8-4 mgm., creatinine are present in 10 c.c. urine. 

 Hence the amount in the 24 hours' quantity is calculated. 



Creatine + Creatinine. 



Though creatine is not normally present in urine, it appears in 

 certain pathological conditions. 



It is estimated by conversion into creatinine as described on p. 168. 



The difference between the estimations of creatinine and creatine 

 + creatinine gives the amount of creatine. 



Benedict l gives the following procedure : 



A volume of urine containing between 7 and 12 mgm. of total 

 creatinine is put into a small flask or beaker together with 10-20 c.c. 

 of N hydrochloric acid and a pinch or two of powdered or granulated 

 lead. The effect of the lead is to prevent pigment formation. The 

 mixture is boiled nearly to dryness over a flame and then evaporated to 

 dryness on a water-bath or by holding the vessel in the hand and heat- 

 ing carefully. The residue is dissolved in 10 c.c. of hot water and the 

 solution rinsed through a plug of cotton or glass wool into a 500 c.c. 

 measuring flask; 20-25 c.c. of picric acid solution are added and 7-8 

 c.c. of 10 per cent, sodium hydrate containing 5 per cent, of Rochelle 

 salt, which prevents turbidity due to the presence of lead hydroxide. 

 After 5-7 minutes the volume is made up to 500 c.c. and the colour 

 compared with the standard. 



J J. Biol. Chem., 191 j, 18, 192. 



