Ammonium in fertilizers – Rapid and reliable determination by thermometric titration

Nitrogen is a primary macronutrient for plants and is a constituent of amino acids and thus proteins. In fertilizers, nitrogen is provided in the form of nitrate or ammonium, as plants are only able to take up these two nitrogen ions. As amino acids can only be built from ammonium, a distinction between ammonium nitrogen and nitrate nitrogen in fertilizers helps to select the right fertilizer for the plants.

Traditionally the ammoniacal nitrogen is determined Kjeldahl digestion followed by titration. In this Application Note, an alternative method is presented, where the ammoniacal nitrogen is determined by a redox titration with sodium hypochlorite. Various solid and liquid NPK fertilizers with ammoniacal nitrogen contents between 1.5 and 13.5% were analyzed. The analysis by thermometric titration is highly robust, requires no sample preparation at all for liquid NPK fertilizers and only minimal sample preparation for solid NPK fertilizers. One determination takes only about 2 minutes.