In order to solve the problem of determining accurate nitrogen content in a sample, Kjeldahl developed a method which involves a two-step reaction: a distillation and a back titration.
He found that ammonium salts can be produced by the reaction between organic compounds and sulfuric acid; this step is a digestion.
Ammonium salts produced from this step were collected and, in a second process, reacted with lye.
The ammonia produced in this step was distilled and dissolved in a standardized solution of hydrochloric acid or sulfuric acid.
Finally, this solution was back titrated with caustic soda to indirectly measure nitrogen.

During the 1880s, Kjeldahl used potassium sulfate to raise the boiling point of the acid and mercury as a catalyst to speed the decomposition.
For the back titration process of the released ammonia, he used boric acid buffer solution.

On 7 March 1883, Kjeldahl presented his method at the Danish Chemical Society.
In order to solve the problem of determining accurate nitrogen content in a sample, Kjeldahl developed a method which involves a two-step reaction: a distillation and a back titration. He found that ammonium salts can be produced by the reaction between organic compounds and sulfuric acid; this step is a digestion. Ammonium salts produced from this step were collected and, in a second process, reacted with lye. The ammonia produced in this step was distilled and dissolved in a standardized solution of hydrochloric acid or sulfuric acid. Finally, this solution was back titrated with caustic soda to indirectly measure nitrogen.
During the 1880s, Kjeldahl used potassium sulfate to raise the boiling point of the acid and mercury as a catalyst to speed the decomposition. For the back titration process of the released ammonia, he used boric acid buffer solution.
On 7 March 1883, Kjeldahl presented his method at the Danish Chemical Society.
Johan Kjeldahl