Determination of Total Ammonium Nitrogen in Pig and Cattle Slurry: Sample Preparation and Analysis

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Abstract
In order to supply the correct amount of ammonium to the crop when slurry is spread on the field, it is necessary to know the ammonium concentration. Slurry is a heterogeneous substance and there is a risk that organic N-compounds and the ionic strength will interfere with the determination of ammonium. The usability of five different methods for the determination of ammonium in solution has been tested on 18 different cattle and pig slurries and compared to a manual distillation titration technique. Colorimetric determination using an autoanalyzer and an automatic titration distillation device using MgO were highly accurate, and the precision was close to 1%. Distillation with NaOH caused interference from hydrolysable organic compounds. An ammonium electrode could be used, but the accuracy was not good. When using the automatic titration distillation device, samples should immediately be transferred to Kjeldahl flasks with water or acidified to prevent loss of volatile ammonia, unless they are to be distilled within 30 min.