288 TITRIMETRIC METHODS 



mixture given above, 150 /xl. acetone containing naphthyl red is 

 added, and titration with 0.05 A^" alcoholic hydrochloric acid is per- 

 formed in the usual manner (page 303). 



AMIDE, PEPTIDE, AND NITRATE NITROGEN 



Borsook and Dubnoff (1939) described methods for amide,. pep- 

 tide, and nitrate nitrogen which were adapted to 0.1 ml. samples 

 containing as little as 0.3 jag. nitrogen. These methods all involve 

 determination of ammonia, a diffusion cell technique, and an electro- 

 metric titration, a glass electrode being used by the authors. 

 Whether or not one wishes to follow this particular procedure for 

 the estimation of ammonia, the initial steps in the methods of Bor- 

 sook and Dubnoff can still be utilized; the details are given below. 



Borsook and Dubnoff Methods for Amide, Peptide, 

 and Nitrate Nitrogen 



Amide Nitrogen 



SPECIAL REAGENTS (in addition to those required for determination of 

 ammonia) 



S N Sulfuric Acid. 



2.9 N Sodium Hydroxide. 



PROCEDURE 



1. Pipette 0.2 ml. sample into a Kjeldahl digestion tube. Add 

 0.1 ml. 3 A^ sulfuric acid, and mix. 



2. Cover with a tin-foil cap and place in a boiling water bath 

 for 3 hr. 



3. After the hydrolysis, cool and add 0.1 ml. 2.9 N sodium 

 hydroxide, mixing well during the addition. 



4. Determine the ammonia nitrogen and subtract from this 

 value the ammonia nitrogen present before hydrolysis as measured 

 by a separate analysis. The difference is the amide nitrogen. 



Nitrate Nitrogen 



SPECIAL REAGENTS (in addition to those required for determination of 

 amide and ammonia nitrogen) 



Devarda Alloy (finely powdered). 

 S5% Sodium Hydroxide. 



