Shanghai Xinzhuang Instrument Co., Ltd. is a leading company that integrates R&D, manufacturing, and sales. With a strong focus on innovation and technological advancement, the company continuously drives strategic, technical, and product innovations, maintaining its leadership in the field of scientific instruments. The company is committed to making meaningful contributions to the progress of human society and striving to build a globally recognized brand. By pushing the boundaries of Chinese scientific instruments, Shanghai Xinzhuang aims to achieve global recognition and excellence.
The Kjeldahl nitrogen method is a widely used analytical technique for determining total nitrogen content in various samples. This standard outlines the procedure for measuring Kjeldahl nitrogen, which includes ammonia nitrogen and organic nitrogen compounds that can be converted into ammonium salts under the digestion conditions specified. These compounds typically include proteins, amino acids, nucleic acids, urea, and similar substances containing nitrogen in a trivalent form. However, it excludes certain nitrogen compounds such as azides, nitrates, nitrites, nitriles, hydrazines, and others that do not react under these conditions.
This method is applicable to the analysis of Kjeldahl nitrogen in industrial wastewater, lakes, reservoirs, and other contaminated water sources. The measurement range varies depending on the concentration of nitrogen in the sample. For low concentrations, larger sample volumes are taken, followed by digestion and distillation, with ammonia determined using spectrophotometry. When the concentration is high, smaller sample volumes are used, and acid titration is employed for the final determination.
The minimum detectable concentration is 0.2 mg/L when using a 10 mm cuvette with a sample volume of 50 mL. The principle of the method involves digesting the sample with sulfuric acid, which converts organic nitrogen into ammonium sulfate. Potassium sulfate is added to raise the boiling point, while mercury salts act as catalysts to speed up the digestion process. After digestion, the solution is made alkaline, and ammonia is distilled and absorbed in boric acid. The ammonia content is then measured by titration or spectrophotometry.
To ensure accuracy, mercury complexes formed during digestion must be broken down using sodium thiosulfate before the distillation step. All reagents used in this method should be of analytical grade unless otherwise specified. Ammonia-free water is essential for accurate results and can be prepared using ion exchange or distillation methods. Common reagents include sulfuric acid, potassium sulfate, mercuric sulfate solution, sodium thiosulfate-sodium hydroxide solution, and boric acid solution.
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