The Kjeldahl method is a means of determining the nitrogen content of organic and inorganic substances.
Although the technique and apparatus have been altered considerably over the past 100 years, the basic principles introduced by Johan Kjeldahl endure today. The Kjeldahl method may be broken down into three main steps:
Digestion - the decomposition of nitrogen in organic samples utilizing a concentrated acid solution. This is accomplished by boiling a homogeneous sample in concentrated sulfuric acid. The end result is an ammonium sulfate solution.
Distillation - adding excess base to the acid digestion mixture to convert NH4 + to NH3, followed by boiling
and condensation of the NH3 gas in a receiving solution.
Titration - to quantify the amount of ammonia in the receiving solution. The amount of nitrogen in a sample can be calculated from the quantified amount of ammonia ions in the receiving solution.