URINE 503 



may be determined and a correction applied, or the ammonia may be 

 removed by means of phosphotungstic acid. Phosphates also inter- 

 fere by obscuring the end-point and are removed by the addition of 

 barium salts. 



It must be borne in mind that polypeptides and still more complex 

 protein derivatives likewise react with formol to a certain degree so 

 that the results do not strictly represent "ammo-acid nitrogen." 



The method is, with some modifications involving the preparation 

 of the solution to be titrated, applicable in the determination of amino- 

 acids in any medium, e.g., urine, protein digests, etc. When poorly 

 dissociated acids, e.g. some fatty acids, are present, these will in part 

 be included in the result and lead to values which are too high. Certain 

 of the amino-acids when present in large amounts will give erroneous 

 results, but in the ordinary urine or digest these errors are either 

 negligible or compensate each other. In the titration of colored solu- 

 tions the control solution which is necessary in this method must be 

 colored to correspond with the color of the unknown solution. 



Procedure. The determination of the amino-acids is carried out as follows : 

 The solution to be analyzed, if carbonates, phosphates and ammonia are absent, 

 is made neutral to litmus (paper) and the solution titrated with formalde- 

 hyde as below. 1 In case carbonates, phosphates or ammonia are present a 

 preliminary treatment is necessary which will vary according to the quantity 

 of ammonia present. 



(a) For Small Amounts of Ammonia. Applicable to most urines. Fifty 

 c.c. of the material under examination is pipetted into a 100 c.c. measuring 

 flask and i c.c. phenolphthalein solution 2 and 2 grams of solid barium chloride 

 are added ; the whole is shaken, to saturate the solution with barium chloride ; 

 saturated barium hydroxide solution is added until the red color of the phenol- 

 phthalein develops and then an excess of 5 c.c. is added. The flask is filled 

 to the graduation mark with water, shaken and permitted to stand for 15 minutes, 

 after which it is filtered through a dry filter. Eighty c.c. of the clear red filtrate 

 (which corresponds to 40 c.c. of the liquid under examination) are placed in 

 a 100 c.c. measuring flask, neutralized to litmus and diluted to 100 c.c. with 

 freshly boiled water. Equal portions of this solution, 40 c.c. (equivalent to 

 1 6 c.c. of the original solution), may be taken for analysis, one for the formol 

 titration and the other for the determination of ammonia nitrogen. 3 



(b) For Large Amounts of Ammonia. After the treatment with phenol- 

 phthalein, barium chloride, and barium hydroxide, and the solution has been 

 diluted to 100 c.c. as in (a) above, the ammonia is distilled off, in vacuo. 4 



1 As a standard of comparison the litmus paper used for neutralization is contrasted with 

 a similar piece dipped in a phosphate solution having a neutral reaction (M/I5 KH 2 PO 4 and 

 M/is Na 2 HP0 4 ). 



2 A solution of 0.5 gram of phenolphthalein in 50 c.c. of alcohol and 50 c.c. of water. 



3 The determination of ammonia may be dispensed with in case a separate determina- 

 tion is made. 



4 For particulars with regard to the distillation, etc., see Henriques and Sorensen: Zeit. 

 physiol. Chem., 64, 137, 1909. 



