Best @ Buchi: Nitrogen Determination with Kjeldahl

Buchi Kjeldahl Distillation and Titration SolutionsThe Best @ Buchi series are information bulletins highlighting the important real-world applications for Buchi products. The first one we present focuses on achieving low detection and quantification limits for nitrogen determination with Kjeldahl. Select here for a PDF version of this Best @ Buchi bulletin.
The Buchi lab equipment used in this research included a Automatic Kjeldahl K-370 (see below), a distillation unit with an integrated titrator, and a Kjeldahl K-371 which is a 24 position autosampler.
Kjeldahl is one of the most commonly used techniques to determine the protein content in food and feed samples. The detection and quantification limits are important characteristics of kjeldahl analytical methods. The impact of the concentration of boric acid, the addition of potassium chloride, and the concentration of the titration solution on the detection and quantification limits were investigated.

Buchi Auto Kjeldahl K-370

Results:  The best results were obtained by using 2% boric acid with 3g potassium chloride per liter. A titration solution of 0.005 M HCl worked best. With these parameters, detection limits for distillation of standard solutions as low as 0.008 mg nitrogen and quantification limits of 0.02 mg nitrogen can be achieved.