Nitrogen and total protein determination in pharmaceutical products are described in the European pharmacopoeia (Ph.Eur.) methods 2.5.9. and 2.5.33. method 7 [1, 2]. In the pharmacopoeia of the United States (USP), nitrogen determination is described in method 461 . 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 boric acid titration. The aim of the following study was to determine the reproducibility and to compare the different titration techniques. Therefore, the nitrogen content of a biotechnologically repared peptide sample for intravenous use was determined by sulfuric acid digestion with the SpeedDigester K-439, followed by steam distillation and titration applying the BUCHI KjelMaster System K-375 / K-376.
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