Kjeldahlmenetelmää

The Kjeldahl method is a standard analytical chemistry procedure for determining the nitrogen content of a sample. Developed by Danish chemist Johan Kjeldahl in 1883, it is widely used in food analysis, agriculture, and environmental monitoring. The method involves several steps. First, the sample is digested in concentrated sulfuric acid, usually at high temperatures, in the presence of a catalyst. During this process, organic nitrogen compounds are converted into ammonium sulfate. Following digestion, the solution is made alkaline, typically with sodium hydroxide, which liberates ammonia gas. This ammonia is then distilled into a receiving solution, commonly boric acid, where it is trapped. Finally, the amount of trapped ammonia is quantified by titration with a standard acid solution. The results obtained are then used to calculate the total nitrogen content of the original sample. The Kjeldahl method is considered a reference method for protein determination, as most proteins contain nitrogen. However, it does not measure non-protein nitrogen, and its accuracy depends on the assumption that all nitrogen in the sample is converted to ammonia, which may not always be true for certain nitrogen-containing compounds.