Improved method of nitrogen determination by indophenol reaction

• Published in: Bunseki kagaku Vol. 10; no. 4; pp. 387 - 392
• Main Authors: NAKAI, Shuryo, TSUCHIYA, Fumiyasu
• Format: Journal Article
• Language: English
• Published: Tokyo Japan Science and Technology Agency 1961
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.10.387

The causes of errors in the indophenol colorimetry for nitrogen determination were made clear. The most important factor was the reaction temperature, which was followed by the method of mixing with antiformin, pH of the reaction mixture, and volume of reagents. In the modified method by the authors, the procedures were improved as follows. 1. All procedures for the determination should be done at room temperature. 2. Digested sample after addition of phenol, NaOH and carbonate buffer should be rapidly poured into a test tube containing antiformin reagent. 3. Quantities of carbonate buffer were increased as to diminish the influence by pH of reaction mixture. 4. The best combination of volumes of phenol and antiformin was used. In the modified method the coefficient of variation of determination was improved to be 1.5%. A large number of determinations was made on nitrogen contents of milk and milk products by this simplified and rapid method.