How it began
Johan Kjeldahl worked at the Carlsberg Laboratory, where his task was to study scientifically the processes involved in making beer. While examining proteins during malt production he devised a new way to determine nitrogen content. He presented it in 1883 at a meeting of the Danish Chemical Society and published it that year in the reports of the Carlsberg Laboratory and in chemical journals abroad.
How it works
The method has three steps. In digestion, a sample is boiled in concentrated sulfuric acid, which breaks it down and leaves the nitrogen as an ammonium sulfate solution. In distillation, an excess of base is added to turn the ammonium into ammonia gas, which is boiled off and condensed into a receiving solution. In titration, the ammonia in that solution is measured, and the nitrogen in the sample is calculated from it.
What changed first
The method was faster and more accurate than any way of measuring nitrogen available at the time. Soon after it was published, different chemists made numerous modifications and improvements to it. In the same year accounts of it also appeared in German in the Zeitschrift fur Analytische Chemie and in English in Chemical News.
Where it stands today
The method handles a wide range of samples in food, feed, beverages, environmental testing, chemicals and pharmaceuticals. Total Kjeldahl nitrogen serves as a stand-in for protein in food and is a required figure in regulatory reporting at many water treatment plants. Bodies including AOAC International, the EPA and ISO have approved it. A maker of the equipment notes that it may not be the fastest method.
