Determination of Amino-acid Nitrogen in Urine. 109 

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Determination of the amino-acid nitrogen in the urine. 

 By S. R. BENEDICT and J. R. MURLIN. 



[From the Cornell University Medical College.] 



Since the abandonment of the Pfaundler method for deter- 

 mination of the amino-acid nitrogen of the urine, the only direct 

 methods proposed which have met with any favor, are the gaso- 

 metric method of D. D. Van Slyke and the titration method of 

 Henriques and Sorensen. In our hands the Van Slyke method as 

 originally described 1 has not proved entirely satisfactory, (1) be- 

 cause of the difficulty of removing all the ammonia after conversion 

 of urea, and (2) because poly-peptids and other condensation 

 products of amino-acids, e. g., hippuric acid, are estimated as well 

 as free amino-acid nitrogen. The method, therefore, probably 

 gives results which are too high. 



The Henriques and Sorensen method as improved by the 

 authors themselves 2 likewise presents some difficulties. For ex- 

 ample, as objected by de Jager and since admitted by Henriques 

 and Sorensen, in the presence of large quantities of ammonia the 

 total titration is less than the sum of the ammonia N and amino- 

 acid N done separately. It is therefore necessary first to remove 

 the ammonia. Henriques and Sorensen recommend for this the 

 method of Krieger and Reich slightly modified. This is essentially 

 the method well known in this country by Shaffer's name. Since 

 the method is based on distillation under diminished pressure, it is 

 not adapted to rapid determinations in a series of urines simul- 

 taneously. Besides, as used by Henriques and Sorensen, we have 

 not been able to obtain as high ammonia figures as by the Folin 

 method. Use of the latter method for removal of ammonia, while 

 perfectly satisfactory for small samples of urine (10 or 20 c.c.) is 

 not satisfactory for a sample large enough to give a titration for 

 amino-acid nitrogen (40-50 c.c). 



Another objection to the Henriques and Sorensen procedure 

 is the difficulty of titration with phenolphthalein in a barium 

 filtrate because of interference of carbon dioxide. 



1 Proc. Soc. Exp. Biol, and Med., 1910, VII, p. 47. 



2 Zeitschr. f. physiol. Chemie, 1909, LXIV, p. 120. 



