Introduction to the principle of Kjeldahl nitrogen analyzer

Kjeldahl nitrogen analyzer is an instrument
that calculates the protein content by determining the nitrogen content in a sample based on the principle of constant nitrogen content in proteins.
Because its protein content measurement calculation method is called Kjeldahl nitrogen determination method, it is called Kjeldahl nitrogen analyzer, also known as nitrogen analyzer, protein analyzer, crude protein analyzer
.
The organic compound is coheated with sulfuric acid so that the nitrogen in it is converted to ammonium
sulfate.
In this step, potassium sulfate is often added to the mixture to increase the boiling point
of the intermediate product.
The end point of the analytical process of the sample is well judged because the mixture becomes colorless and transparent (dark at first) and a small amount of sodium hydroxide is added to the resulting solution and then distilled
.
This step converts the ammonium salt into ammonia
.
The total amount of ammonia (directly determined by the nitrogen content of the sample) is determined by the reverse titration method: the end of the condensing tube is immersed in a boric acid solution
.
Ammonia reacts with acid, while excess acid is titrated
with sodium carbonate under the indication of methyl orange.
The result obtained by titration is multiplied by a specific conversion factor to obtain the result
.
Kjeldahl nitrogen analyzer instruments use Kjeldahl methods to detect ammonia, protein nitrogen content, phenol, volatile fatty acids, sulfur dioxide, ethanol and other contents
in grains, food, feed, water, soil, silt, sediments and chemicals.
With a fairly good cost performance, only the titration process requires manual operation, which is very suitable for routine testing
in laboratories and inspection institutions.
Widely used in food, crops, seeds, soil, fertilizers and other samples of nitrogen content or protein content analysis
.