PROTEINS 



THE QUANTITATIVE DETERMINATION OF ALIPHATIC 

 AMINO GROUPS 



Method of Van Slyke. 1 Principle. This method for the determination of 

 aliphatic amino nitrogen is based on the measurement of the nitrogen gas evolved 

 in the reaction, 



RNHH-HNO 2 =ROH+N 2 +H 2 0. 



During the process the following reaction also takes place, the nitrous acid solution 

 decomposing spontaneously with the formation of nitric oxide. 



2 HNO 2 =HNO 3 +NO. 



FIG. 34. VAN SLYKE AMINO NITROGEN 

 APPARATUS. 



FIG. 35. SECTION or VAN SLYKE 

 APPARATUS. 



This latter reaction is utilized in displacing all the air of the apparatus with nitric 

 oxide. The amino solution is then introduced, evolution of nitrogen mixed with 

 nitric oxide resulting. The oxide is absorbed with alkaline permanganate solution 

 and the pure nitrogen measured in a special gas burette shown in the figure. 

 Procedure. The determination is carried out in three stages: 

 i. Displacement of Air by Nitric Oxide Water from F (see Figs. 34 and 35), 

 fills the capillary leading to the Hempel pipette and also the other capillary as 

 far as c. Into A one pours a volume of glacial acetic acid sufficient to fill one- 

 1 Van Slyke: Jour. Biol. Chem., 12, 275, 1912; 16, 121 and 125, 1913. 



