The ammonium sulphate present in the digested sample is converted into ammonia gas, heated and distilled. The ammonia gas is led into an acid trapping solution where it dissolves and becomes a trapped ammonium ion once again. Using the Kjeldahl distillation, nitrites and nitrates are not detected. In order to quantify these elements, a reduction of the sample is necessary (using Devarda alloy) before the Kjeldahl digestion stage.
VELP Kjeldahl distillation units offer different levels of automation, from entry-level distillation to distillation with automatic reagents addition and residues aspiration, up to fully automated system with integrated colorimetric titration.