Kjeldahlin

Kjeldahlin is a chemical process used for the quantitative determination of nitrogen content in organic compounds. Invented by the Danish chemist Johan Kjeldahl in 1883, the method is widely employed in analytical chemistry for the analysis of food, feed, soil, and water, as well as in the pharmaceutical and environmental industries. The Kjeldahl method involves the digestion of a sample in concentrated sulfuric acid, which converts organic nitrogen to ammonium sulfate. The ammonium sulfate is then heated with a strong base, such as sodium hydroxide, to liberate ammonia gas. This ammonia gas is subsequently trapped in a solution of boric acid, where it reacts to form ammonium borate. The amount of ammonia, and thus the nitrogen content of the original sample, is determined by titrating the ammonium borate with a standardized solution of acid, typically hydrochloric acid or sulfuric acid. The end point of the titration is usually detected using an indicator like methyl red. The Kjeldahl method is considered a reference method for determining total nitrogen, though it does not measure certain forms of nitrogen, such as nitro and azo groups, or inorganic nitrogen compounds like nitrates and nitrites, unless these are first reduced to ammonia. Despite its limitations, the Kjeldahl method remains a reliable and widely accepted technique for nitrogen analysis due to its accuracy and robustness.