Kjeldahl finds a method... Science

A method for the ages...

Danish chemist Johan Kjeldahl (1849-1900) painted by Otto Haslund (1842-1917); Original color painting located in the boardroom of the Carlsberg Laboratory in Copenhagen. Photo: Wikimedia Commons  

If the discovery of the structure of DNA that we looked at last week is etched in science history through the announcement that was made in a pub, what we will be discussing today again has a pub-connect. For the Kjeldahl method to determine nitrogen content in an organic compound was developed initially to solve a beer-related problem.

Born to a medical officer in a small Danish village called Jaegerspris, Johan Kjeldahl went to the Royal Polytechnic College in Copenhagen after completing his schooling. He received his Master’s degree in natural sciences and took the post of an assistant at a chemical laboratory of the Royal Agricultural College in Copenhagen in 1873.

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What is a round bottom flask with a long wide neck that is used in the determination of nitrogen called? Send your answers to ganesh.a.s@thehindu.co.in with your details. [subject: nitrogen]
Last week’s answer
Rosalind Franklin, who did not win the Nobel Prize, was also involved in determining the double-helix structure of DNA. Lakshmi K.Shanmughan of Class VI, Bharatiya Vidya Bhavan, Bhimavaram was among those who got it correct. Congratulations!
Danish chemist C. T. Barfoed was the head of the department here and his laboratory was primarily concerned with analytical chemistry, both qualitative and quantitative. Barfoed realised that his young assistant was not only adept at determining the exactness in chemical research, but also greatly appreciated its significance.

So when J. C. Jacobsen, the director of the Carlsberg Brewery and a friend of Barfoed, realised the value of applied chemistry and set up a chemical laboratory, Kjeldahl was appointed a chemist there on Barfoed’s suggestion in 1875. This lab was devoted to methods and processes that were of particular interest to the brewing industry. Kjeldahl soon became absorbed in the protein content of grains used in the industry (protein content has a say in the beer produced), which in essence implied finding out the nitrogen content of the samples.

Combustion analysis was employed during these times to find the C: H: N (carbon, hydrogen, nitrogen) ratio of an organic compound. While the art had been perfected in the case of carbon and hydrogen, nitrogen proved to be trickier owing to contamination by air and incomplete combustion giving out nitrogen oxides.

As Kjeldahl’s work on protein required a series of analyses, he wanted to do away with combustion all together. He found that he could generate ammonium ions quantitatively by digesting the samples in concentrated sulphuric acid in the presence of permanganate.

The digested solution was diluted and transferred to a round-bottomed, long-necked distillation apparatus, which also now bears Kjeldahl’s name. The ammonia produced on reaction with alkali was distilled into standard acid, which when back titrated could indirectly measure the amount of nitrogen.

Photo: Wikimedia Commons

Photo: Wikimedia Commons  

In the Carlsberg annual report for 1882-82, Kjeldahl included this method and presented it on March 7, 1883 to the Danish Chemical Society. News spread like wildfire and within no time the Kjeldahl method of determining nitrogen content was universally adopted.

Even though other methods that are more accurate and faster have evolved over the years, Kjeldahl method continues to be in use as it is extremely versatile. Be it food or feed (grains, milk, vegetables, etc.), beverages or industry produce (paper, fertilisers, etc.), any sample can be handled by this method to find its nitrogen content.

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Printable version | Dec 2, 2021 3:53:03 PM | https://www.thehindu.com/in-school/sh-science/a-method-for-the-ages/article8320677.ece

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