Kjeldahl Nitrogen Analyzer and Precautions During the Digestion Process
Proteins are essential components of human cells, making the intake of protein from food highly important for human life activities. Therefore, determining the protein content in food is also a crucia
Proteins are essential components of human cells, making the intake of protein from food highly important for human life activities. Therefore, determining the protein content in food is also a crucial task. With the development of instrument technology, the Kjeldahl Nitrogen Analyzer is now commonly used for protein determination. Numerous experiments have shown that the Kjeldahl Nitrogen Analyzer can overcome the shortcomings of manual methods, providing results that conform to international standards. It is fast, stable, and highly recommended as an essential tool for determining protein content.
However, it is important to note that the pretreatment digestion process is also critical. This requires the use of an intelligent digestion furnace. To ensure the accuracy of the results when using the Kjeldahl Nitrogen Analyzer to measure protein content, the following precautions must be observed:
The digestion time should be carefully controlled. If the time is too long, ammonia may be lost; if the digestion time is too short, the digestion will be incomplete, leading to a lower total nitrogen value. As a general guideline, start with a low flame and maintain a temperature of 420°C for about 2 hours for adequate digestion.
When placing the sample into the digestion tube, ensure that it does not adhere to the neck of the tube. If it does, rinse it down with a small amount of water to avoid incomplete digestion, which may result in lower test results.
The ratio of potassium sulfate to sulfuric acid is crucial for successful digestion. It affects the boiling point of the acid and the required digestion time. Adding potassium sulfate can raise the temperature and accelerate the breakdown of organic matter, but too much potassium sulfate can increase the boiling point, leading to the breakdown of ammonium bisulfate and the release of ammonia, causing nitrogen loss. Therefore, when the sulfuric acid is consumed or when the sample contains high fat content, the amount of sulfuric acid should be increased.
If the sample has a high sugar or fat content, control the heating temperature during digestion. You may add a small amount of n-octanol, liquid paraffin, or an anti-foaming agent to reduce foam formation.
If the sample is difficult to digest to a clear and transparent solution, cool the digestion tube, add a few drops of hydrogen peroxide, and then continue heating until complete digestion is achieved.
Before using the nitrogen analyzer, run a blank distillation to eliminate any residual ammonia in the tubing, which helps reduce errors.
The intensity of the heat source plays a significant role in rapid and complete digestion. During the entire digestion process, avoid using a high flame. Instead, gradually heat with a moderate boiling temperature, starting with a low flame, to prevent protein on the walls from losing nitrogen due to the absence of sulfuric acid.
When placing the digested sample tube into the distillation chamber, prevent ammonia loss by ensuring that the solution does not overflow during distillation. Before placing the digestion tube into the sealing ring, gently rotate the tube by hand to ensure a tight seal.
Prior to using the alkali delivery tube of the nitrogen analyzer, rinse it with a sodium hydroxide solution. After use, rinse it thoroughly with distilled water. Do not leave alkali in the tubes for prolonged periods to prevent blockages after storage.
For companies still using Kjeldahl Nitrogen Analyzers, the above precautions are of significant reference value.
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