552 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Amino Acids. 



The exact estimation of the amino acids in urine is troublesome to effect. 

 A very close approximation is given by the difference between the ammonia 

 and " ammonia " values. It is more accurately obtained by performing the 

 ammonia estimation by Folin's method using 50 c.c. of urine and 50 c.c. of 

 baryta water. The remainder in the cylinder is washed into a 250 c.c. 

 measuring flask, diluted to the mark, mixed and filtered; 100 c.c. portions of 

 the filtrate are neutralised to phenolphthalein with - 2N hydrochloric acid ; 

 10 c.c. of neutralised formalin are added and the solution is titrated with -iN 

 alkali. 



The value multiplied by f-J is the amount in 25 c.c. of urine. Hence the 

 amount in the 24 hours' quantity. It is best expressed in terms of nitrogen'. 



Total Nitrogen. 



This estimation is carried out by Kjeldahl's method as described 

 *>n pp. 35-38. 



5 c.c. of urine are heated with 10 c.c. of pure sulphuric acid and 

 a small crystal of copper sulphate till oxidation is complete. 



The ammonia formed is distilled off and collected in 50 c.c. 

 iN H 2 SO 4 . 



Titration with 'iN NaOH gives the amount of -iN NH 3 in 5 c.c. of 

 urine. 



Hence the amount of nitrogen in the 24 hours' quantity (2000 c.c), 

 e-g. 



Suppose 100 c.c. -iN H 2 SO 4 were taken and 66 c.c. -iN NaOH used. 

 Difference = 34 c.c. -iN H 2 SO 4 = 34 c.c. -iN NH 3 = 34 c.c. -iN nitrogen. 

 = 34 x 0-0014 gm. N in 5 c.c. of urine. 

 = 19*04 gm. in 2000 c.c. 



Urea. 



(1) The most rapid method of estimating urea is the hypobromite 

 method as described on p. 1 34. 



5 c.c. of urine are treated with 25 c.c. of hypobromite solution and 

 the volume of nitrogen evolved is measured. 



As 354 c.c. of nitrogen at o and 760 mm. pressure are evolved 

 by I gm. of urea or -47 gm. of nitrogen as urea, the amount of urea 

 or urea nitrogen in 5 c.c. urine can be calculated. Hence the amount 

 in the 24 hours' volume. 



Other substances such as ammonia, creatine, uric acid, evolve 

 nitrogen under these conditions, but it is very small in comparison. 



The method gives good comparative values for clinical work. 



(2) The most accurate method of estimating urea is by the hydro- 

 lysis of the urea by urease. 



It is carried out exactly as described on p. 136 using 5 c.c. urine 

 and collecting the ammonia in 50 c.c. of 'iN acid containing a few 

 drops of alizarin red. 



Since the ammonia of the urine is included in this estimation its 

 amount must be deducted. 



