What Is The Principle Of Kjeldahl Nitrogen Determination Pros And Cons?

Technical Knowledge 2022-02-23 09:15:03
The Kjeldahl method was first proposed in 1883 by the Danish chemist Kedall. Due to the simple equipment requirements, it has become a classic method for protein determination since it was proposed, and is widely used in protein detection. The Kjeldahl method can only convert organic nitrogen into inorganic ammonium through high-temperature digestion with sulfuric acid, while nitrate nitrogen (such as nitrate and nitrite) cannot be converted.

Therefore, the Kjeldahl method is suitable for foods, agricultural products, cosmetics, medicines, etc. that do not contain nitrate nitrogen. This article introduces in detail what the principle of Kjeldahl nitrogen determination is and the advantages and disadvantages of Kjeldahl nitrogen determination method.

1. The principle of Kjeldahl nitrogen determination

The Kjeldahl method is a method for determining the total nitrogen in a compound or mixture. Digestion of samples with concentrated sulfuric acid under catalyst conditions converts organic nitrogen to inorganic ammonium salts, and then converts ammonium salts to ammonia under alkaline conditions. It is distilled with water vapor and absorbed by excess boric acid solution, and then titrated with standard hydrochloric acid to calculate the amount of nitrogen in the sample. Since the nitrogen content of protein is relatively constant, the protein content can be calculated from its nitrogen content, protein content = nitrogen content * 6.25.

2. Advantages and disadvantages of Kjeldahl method


1. Can be used in protein analysis of all foods;

2. The operation is relatively simple;

3. The experiment cost is low;

4. The results are accurate, and it is a classic method for protein determination;

5. A modified method (micro Kjeldahl method) can be used to determine trace amounts of protein in the sample.


1. The final determination is total organic nitrogen, not protein nitrogen;

2. The experiment time is too long (at least 2H to complete);

3. Poor accuracy, the accuracy is lower than the biuret method;

4. The reagents used are corrosive.

Among them, the Kjeldahl method is used to determine the protein content of the instrument is the Kjeldahl analyzer.

Tags Kjeldahl analyzer Kjeldahl nitrogen determination Kjeldahl method protein determination determining the total nitrogen
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