Kjeldahl’s Method for Estimation of Nitrogen

This is a very convenient method but its use is restricted. This method but it’s use is restricted. This method is suitable for estimating nitrogen in those organic compounds in which nitrogen is linked to carbon and hydrogen. The method is not used in the case of nitro, azo and azoxy compounds. The method is extensively used for estimated nitrogen in food, fertilizers and agricultural products.

Principle:- the method is based on the fact that when the nitrogenous compound is heated with concentrated sulphuric acid in presence of copper sulphate, the nitrogen present in the compound is quantitatively converted to ammonium sulphate. The ammonium sulphate so formed is decomposed with excess of alkali and the ammonia evolved is estimated volumetrically. The percentage of nitrogen is then calculated from the amount of ammonia.