Ammonia. 



The estimation of ammonia in urine until 1902 was a matter ot 

 considerable trouble on account of the length of time required to per- 

 form an analysis, but in that year Folin introduced his aeration method 

 for removing the ammonia from urine made alkaline with sodium 

 carbonate. 



Folin' s Method. 



The apparatus required for this estimation is the same as that used in 

 estimating urea by means of urease (p. 136). 



25 c.c. of urine are placed in the tall gas cylinder together with 

 i gm. of anhydrous sodium carbonate and a few c.c. of toluene or paraffin. 

 The cylinder is connected to the receiver containing 10 or 20 c.c. of 'iN 

 acid coloured with a few drops of alizarin red as indicator. 



The cylinder is placed in a bath at 40 and a good air current is passed for 

 i hour (longer if the suction is not rapid). The liquid in the receiver is 

 titrated with 'iN alkali. 



The results are expressed in gm. of NH 3 , or better in terms of nitrogen as 

 ammonia per 24 hours' quantity of urine (2000 c.c.) Thus suppose 6-0 c.c. 

 alkali were required. 

 10 6*0 = 4*0 c.c. *iN NH 3 



= 4 x -0017 gm. NH 8 or 4 x -0014 gm. N as ammonia 



2000 2000 



= 4 x -0017 x - gm. NH 3 ,or4 x -0014 x - - gm. N as ammonia per 24 hours. 



Various modifications of this method have been put forward, e.g. using 

 baryta instead of sodium carbonate. In this case the amount of amino acids 

 can be estimated in the remainder (below). 



Estimation of "Ammonia". Ammonia -f Amino Acids. 



In 1908 Malfatti showed that the ammonia in urine could be 

 rapidly estimated by titrating neutralised urine after the addition of 

 formaldehyde. The method depends upon the fact that when a neutral 

 solution of an ammonium salt is treated with formaldehyde, combination 

 occurs with the formation of hexamethylenetetramine (urotropin) with 

 the liberation of a corresponding amount of acid which can be titrated 

 with 'iN NaOH. The reaction is 



4 NH 4 C1 + 6CH a O = N 4 (CH 2 ) 6 + 6H 2 O + 4 HC1 

 4 HC1 + 4 NaOH = 4 NaCl + 4 H 2 O. 



The amount so obtained is higher than the value obtained by the 

 Folin method and is due to the presence in the urine of small amounts of 

 amino acids which also react with formaldehyde (p. 145). The result 

 is therefore the amount of ammonia and amino acids. 



Since the amino acids are present only in very small amounts, the 

 value can be used as an expression of the ammonia content. The 

 method is particularly useful for clinical work. 



Procedure. 



To the neutralised urine remaining after the acidity estimation are 

 added 10 c.c of formalin which has been diluted with 2 volumes of 

 water and neutralised with -iN alkali to phenolphthalein. 



The pink colour of the urine disappears ; -iN alkali is run in from 

 a burette until a permanent pink colour is again obtained. The number 

 of c.c. required is noted. 



The result is expressed in gm. of NH 3 or gm. of ammonia N. 



