Kjeldahl nitrogen determinations are performed on a variety of food substances. The Kjeldahl method may be broken down into three main steps: digestion, distillation, and titration.
1. Digestion: is accomplished by boiling a homogeneous sample in concentrated sulphuric acid. The end result is an ammonium sulphate solution.
2. Distillation: excess base is added to the digestion product to convert the ammonium salt to ammonia.
3. Titration: the amount of nitrogen in a sample can be calculated from the quantified amount of ammonia in the receiving solution. The ammonia is captured either with a carefully measured excess of a standardised acid solution (back titration) or a boric acid solution (direct titration)