What is the Kjeldahl method?

Scientists use the Kjeldahl method to analyze the percentage of organic nitrogen in the substance. Nitrogen levels can then be used to determine the amount of protein. The full name of the method is Kjeldahl method of nitrogen analysis - sometimes a protein analysis is sometimes used instead of nitrogen analysis, but the terms apply to the same method.

Chemist Johan Kjeldahl first introduced his method of Danish chemical society in 1883. He found that because nitrogen is the main element of the protein, nitrogen analysis could be used to determine the amount of protein in the substance. It has improved since then, but the basic method remains in place.

The Kjeldahl method consists of three steps, commonly called digestion, distillation and titration. Digestion spreads nitrogen over ammonia and distillation separates ammonia from other components. The amount of ammonia is calculated using titration, then the amount of nitrogen and protein can be calculated on the basis of ammonia.

During the step of digestion is a small sample of a substance to be analyzed this mixture warms upAt a very high temperature - up to 750 ° F (about 400 ° C) - about an hour, then cool. The reactions that take place in the heated mixture decompose large molecules into smaller components, including ammonium ions.

The distillation step transforms ammonium ions into ammonia gas by adding sodium hydroxide to the mixture. Then the solution temperature increases and converts ammonia to volatile gas that rises in steam. The Para is captured in a solution such as hydrochloric acid or borithic acid.

ammonia trapped in acid neutralizes a part of the acid, which means it reduces pH. The amount of acids that this neutralization is titrated by a base such as sodium hydroxide. A dye is added to the acid and ammonia solution that changes color when the pH is changed. The acid is then added to a small amount of base until the solution changes in color. The amount of base needed to achieve this end point can be used to calculate the quantityAmmonia in the original solution.

To calculate the amount of nitrogen, the scientist must first know the number of molds of acid and base that were present in the final solution. The subtraction of moths of the base from the moths of acid gives moths ammonia. The ammonia moths in the final solution are the same as nitrogen moths, so this number is multiplied by the 14 - atomic weight of nitrogen - to find a grams of nitrogen.

The

percentage of nitrogen is located by the distribution of nitrogen grams with the total grams in the original sample and multiplying 100. Protein Kjeldahl protein method detects the multiple percentage of nitrogen with conversion factor. This conversion factor is usually 6.25, with the exception of several substances such as wheat and dairy products.