Nitrogen and total protein determination in pharmaceutical products are described in the European Pharmacopoeia (Ph. Eur.) and in the Pharmacopoeia of the United States (USP). Therein, different titration techniques are specified. The Ph.Eur. is using back titration in the presence of the indicator methyl red mixed solution and the USP is using potentiometric and colorimetric boric acid titration.
In this application note, the three different titration techniques were compared and the reproducibility was determined. The nitrogen content of two toxoid samples was determined by sulfuric acid digestion using the KjelDigester K-449 followed by steam distillation and titration applying the BUCHI KjelMaster System K-375 / K-376.