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Scientist Highlight: Johan Kjeldahl

They say science runs in the family, and this was certainly the case for Johan Gustav Christoffer Thorsager Kjeldahl! Son of a physician (Jørgen Kjeldahl), Johan was born in Jægerspris, a small town on the Northern part of the island of Zealand in eastern Denmark. He was educated at the Roskilde Gymnasium and went on to study applied natural sciences at the Royal Polytechnical College in Copenhagen where he received his Masters degree in 1973, with high honours.

His first position was an assistant within the chemical laboratory of C. T. Barfoed, based at the Royal Agricultural College in Copenhagen. The lab was primarily focused on analytical chemistry (both quantitative and qualitative), and Kjeldahl honed his skills whilst developing a talent for ‘exactness’ in chemical research. Barfoed recognised ability within his assistant, and when his friend Mr J. C. Jacobsen recognised the value of analytical chemistry in brewing and set to open a lab within his factory, Kjeldahl was recommended to run the operation. On October 1st, 1876, Kjeldahl was officially appointed the Head of the Chemical Department of the Carlsberg Laboratory.

It didn’t take long for Kjeldahl to become absorbed in the analysis of protein content for grains used within the industry during malt production (known to have a direct impact on the amount of beer being produced – less protein = more beer!). The way to ascertain protein content at the time relied on combustion analysis to work out the ratio of carbon, hydrogen, and nitrogen of organic compounds. This method was often problematic for nitrogen analysis due to contamination and incomplete combustion, leading to the production of nitrogen oxides.

Kjeldahl was determined to develop a method that did not require combustion of the sample. He discovered that he could generate ammonium ions through introducing and digesting samples with concentrated sulphuric acid in the presence of permanganate.

The resultant digested solution was then transferred to a specialised long-necked round bottom flask, now known as Kjeldahl’s Flask. Reaction with an alkali formed ammonia would then be distilled into a standard acid (HCl or H2SO4) and back-titrated, in order to indirectly calculate the nitrogen content.

The method was first described in the 1882 Carlsberg annual report and on March 7th, 1883, Kjeldahl presented his method and research findings to the Danish Chemical Society. It didn’t take long for his method to spread around the world and become the gold-standard method for nitrogen/protein analysis!

Although Kjeldahl died on the 18th of July 1900, his method is still used frequently today due to its versatility when it comes to protein analysis.

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