Page 85 - Analytical Chemistry I E-book
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Determination of nitrogen-containing compounds
Kjeldahl Method
• Nitrogen occurs in a wide variety of substances of interest in research,
industry, and agriculture.
• Examples include amino acids, proteins, food products, drugs, fertilizers,
explosives, and dyes.
• The most common method for determining organic nitrogen is the Kjeldahl
method , which is based on acid-base titration.
• The Kjeldahl method consists of three steps: digestion , distillation and
titration.
• Digestion: The purpose of this step is to break down the bonds that hold the
atoms together, and convert large molecules into smaller ones. The sample is
decomposed by boiling the sample with concentrated sulfuric acid (H2SO4).
As the organic material is decomposed, the carbon is converted to carbon
dioxide, the hydrogen is converted into water and the nitrogen to ammonium
ions. The end result is ammonium sulfate solution.
