The Kjeldahl analysis is extremely versatile, as it can handle a very wide range of samples from food & feed (grain, meat, fish, milk, dairy, fruit, vegetables), beverages, environmental (agriculture, oilseeds, soil, fertilizers, water, wastewater, sludge) to chemical and pharmaceutical industries (paper, textiles, rubber, plastic, polymer).
TKN in Environmental Analysis
Total Kjeldahl nitrogen (TKN) is the sum of organic nitrogen, ammonia (NH3), and ammonium (NH4+) in the chemical analysis of soil, water and wastewater. To calculate Total Nitrogen (TN), the concentrations of nitrate-N and nitrite-N are determined and added to the total Kjeldahl nitrogen.
Today, total Kjeldahl nitrogen is a required parameter for regulatory reporting at many water treatment plants.
TKN and Proteins
Total Kjeldahl nitrogen is used as a surrogate for protein in food samples. The conversion from TKN to protein depends on the type of protein present in the sample and what fraction of the protein is composed of nitrogenous amino acids.
However, the range of conversion factors is relatively narrow. Example conversion factors, known as N factors, for foods range from 6.38 for dairy and 6.25 for meat, eggs and corn to 5.70 for wheat flour, and 5.46 for peanuts.
The secret of a correct TKN determination
In most cases, the key to a successful Kjeldahl analysis can be the sample preparation step (before the digestion phase).
This method might not be the fastest method to use but thanks to the high reliability will always give satisfactory results if performed correctly (and following Standards).