Almost all food and animal feed contains nitrogen/protein. The protein content is calculated from the percentage of nitrogen determined in a sample, and it is a key criterion for the quality and price of a product. This means that this analysis is very important to the food and animal feed industry.
After analytical testing, products are labelled with the relevant nutritional information for consumers. This declaration is subject to mandatory regulations in national and international laws for producers.
The nitrogen/protein analysis according to Kjeldahl is up to date still the reference method in analytics. With its high degree of versatility, the method is suitable for many applications, e.g. food analysis, feed analysis, soil or water analysis. In addition to the versatility, the very high precision also speaks for the method. Particularly in case of highly inhomogeneous sample material, there is hardly any alternative to Kjeldahl due to the high weight of the sample.
While acid digestion according to Kjeldahl destroys the organic sample in a rather rustic way, combustion offers a more elegant and time-saving option. The sample is oxidised in a controlled manner and the resulting gaseous products are subjected to further analysis.