What is a Kjeldahl digestion for nitrogen determination?
Samples are digested in a solution of sulfuric acid, potassium sulfate and a catalyst (mercuric oxide or cupric sulfate). Organic nitrogen compounds are converted into ammonium. Kjeldahl nitrogen is the sum of organic nitrogen and ammonia nitrogen. Nitrogen can be determined by using an FIA system, where the sample pH is raised to a basic pH. The in-line neutralization of the sample converts the ammonium to ammonia, which reacts with a series of reagents to produce a reaction product, the absorption of which is directly proportional to TKN concentration.
