The Kjeldahl method is recognized as the most accurate in determining the total nitrogen content of solid and liquid samples. Based on the mineralization of the test organic compound in concentrated sulfuric acid at the boiling point of this acid. The test substance is oxidized to carbon dioxide and water, and the nitrogen in it is released as ammonia, which forms an ammonium salt in the presence of sulfuric acid.

Setting limits - up to 1 mg Kjeldahl nitrogen in the test sample.The best results are obtained when the sample is 10-15 mg of ammonium nitrogen.