Kjeldahl’s nitrogen determination is still part of the European Pharmacopoeia (Ph. Eur. 2.5.9 “Determination of Nitrogen by sulfuric acid digestion” or monograph “Urea”) and the USP (USP <461> “Nitrogen determination”). The method was developed back in 1883 by the chemist Johan Kjeldahl and can be used for many different nitrogen-containing substances.

In the first step, carbon (C) is oxidized to carbon dioxide (CO2) and sulphuric acid (H2SO4) is reduced to sulphur dioxide (SO2) by boiling the sample with a catalyst and an excess of sulphuric acid. The nitrogen is bound in the solution in the form of ammonium sulphate. The next step is water vapor distillation. By adding a strong base (usually NaOH), the sulphuric acid is neutralized, and ammonia is released. Using water vapor distillation, this is quantitatively introduced into an acid template. Finally, the nitrogen content of the sample can be determined by titration.

We are pleased to be able to include this analytical method in our portfolio from 2025. If the determination of nitrogen using Kjeldahl is relevant for your products or starting materials, we will be glad to advise you.