Johan Kjeldahl

Johan Kjeldahl

Johan Gustav Christoffer Thorsager Kjeldahl (born August 16, 1849 in Jægerspris ; † July 18, 1900 in Tisvilde ) was a Danish chemist who mainly dealt with the sugar and protein metabolism in plants and the development and improvement of chemical analysis methods. From 1876 until his death, he headed the chemistry department of the Carlsberg Laboratory in Copenhagen and became known for developing a method for measuring the nitrogen or protein content of organic samples .

This method, named Kjeldahl's nitrogen determination or Kjeldahlometry after him, found practically universal dissemination and acceptance in analytical chemistry shortly after its introduction . Especially in the field of food chemistry it has been established as a reference standard for determining the protein content up to the present. Johan Kjeldahl was accepted for his work in the Royal Danish Academy of Sciences and in the Academy of Sciences in Christiania and was awarded the Knight's Cross of the Dannebrog Order .

Life

education

Johan Kjeldahl in his laboratory; Reproduction of a picture by Otto Haslund, 1896–1897

Johan Kjeldahl was born in 1849 as the son of the district doctor and later judicial councilor Jørgen Pedersen Kjeldahl (1805–1899) and his wife Johanne Georgine, née. Lohmann (1810–1910) was born in Jægerspris on the island of Zealand . He graduated from the State High School in Roskilde by 1867 and then studied at the Polytechnic School ( Polyteknisk Læreanstalt ) in Copenhagen , currently Denmark's Technical University , from which he graduated in 1873 with the state examination as a candidate in applied science. He then worked for two years in the chemical laboratory at the Agricultural College ( Landbohøjskole ) in Frederiksberg as an assistant to Christen Thomsen Barfoed , who focused on chemical analysis and who published Barfoed's sample in 1873 to distinguish between monosaccharides and di- , oligo- or polysaccharides .

Worked at the Carlsberg Laboratory

In May 1875, after Barfoed recommended him to the founder of the Carlsberg brewery Jacob Christian Jacobsen , Johan Kjeldahl moved to the Carlsberg Laboratory , which was established in the same year and where he headed the chemistry department from October 1876 until his death. He was initially concerned with technical control examinations in the context of beer production , but later turned to scientific issues. Among his students was the botanist and physiologist Wilhelm Johannsen , who worked at the Carlsberg Laboratory from 1881.

As Johan Kjeldahl was extremely critical of his own research and demanding in terms of checking and validating his results, he published only a few papers, especially in the later course of his career. In addition, in the last few years of his life he occasionally suffered from depression , which caused his work to be interrupted due to repeated recovery cures. He remained unmarried all his life and, according to historical traditions, was considered shy and modest, as well as friendly and helpful towards his co-workers.

death

Johan Kjeldahl died in July 1900 about a month before his 51st birthday while bathing in Tisvilde , a holiday and recreation spot on the Danish Kattegat coast (for the cause of death, see notes on the literature). His successor at the Carlsberg Laboratory was Søren Sørensen , who headed the chemical department until 1938.

Scientific work

Studies on beer production

In his first years at the Carlsberg Laboratory, Johan Kjeldahl devoted himself in particular to the analysis of beer and wort as well as investigations into the influence of temperature and other external factors on the activity of sugar-forming enzymes . In the years 1878, 1879 and 1881 he published three treatises in the reports of the laboratory ( Meddelelser fra Carlsberglaboratoriet ) and described, among other things, an improvement in the titration with Fehling's solution used for sugar detection . His initially mainly application- related work on enzymes also led him to plant physiological studies on the metabolism of carbohydrates and to investigations of the enzyme invertase , then called "invertin" , which is sometimes also referred to as "saccharase".

The Kjeldahl nitrogen determination

Representation of the original Kjeldahl apparatus for his method for nitrogen determination; Woodcut by Johan Frederik Rosenstand, published 1883

Johan Kjeldahl became known in particular through the Kjeldahl nitrogen determination he presented in 1883 , which he developed from 1881 to investigate the protein transformation during the germination of plant seeds and to be able to determine the protein content of grain during the brewing process . In accordance with the guidelines for employees of the Carlsberg Laboratory that no result of theoretical or practical significance should be kept secret, he first presented the process to the Danish Chemical Society ( Kemisk Forening ) in a lecture on March 7, 1883. He also published it in the same year in the reports of the Carlsberg Laboratory and in the journal for analytical chemistry .

In addition to its original application, the method made it possible to determine the protein content in a large number of foods , environmental samples and other test material of animal or plant origin . Shortly after its introduction, it also made it possible to work on biochemical questions about protein metabolism in living beings, the investigation of which had previously not been possible or only with significantly more complex and lengthy methods. With the help of the method, other scientists were able to show, for example, that physiologically occurring proteins contain practically no azo , nitro and nitroso groups. The basis of this proof was that the nitrogen contained in these functional groups , in contrast to nitrogen in amino groups, cannot be converted directly with sulfuric acid to ammonium sulfate , the first step in Kjeldahl's nitrogen determination, but must be reduced beforehand, and that a previous reduction does not lead to any or resulted in only minor differences in the measured nitrogen content.

The Kjeldahl nitrogen determination was quickly improved by other scientists. In 1885, for example, Hermann Wilfarth described the use of metallic catalysts to accelerate the reaction, and Jan Willem Gunning four years later the addition of potassium sulfate . Several thousand publications appeared in the following decades on further optimizations such as the use of a higher reaction temperature and adaptations to certain sample materials. The German entrepreneur Carl Heinrich Gerhardt from Bonn brought the first devices to carry out the method on the market as early as 1884 .

More work

Johan Kjeldahl himself used the method he had developed for measuring nitrogen only occasionally and did not carry out any systematic studies on protein chemistry.In the following years, he was mainly concerned with investigating the hydrolysis of starch . In addition, he described the influence of oxygen as an important source of error in the determination of sugars by reducing copper salt solutions . Through this work he contributed to the revision of the data known at the time on the reducing properties of various carbohydrates. In further studies he investigated the optical rotation ability of vegetable proteins and also demonstrated the amino alcohol choline as a component of beer.

Reception and aftermath

Meaning of his life's work

The beginning of the 1883 publication on Kjeldahl's nitrogen determination in the Zeitschrift für Analytische Chemie

The method for nitrogen measurement developed by Johan Kjeldahl found almost universal distribution within a very short time due to its broad applicability, simple apparatus implementation and high precision and reproducibility . The method is therefore an important contribution to the development of organic chemistry at the end of the 19th century and, at that time, allowed, among other things, the precise determination of the protein content of body fluids in the field of physiological chemistry or clinical chemistry for the investigation of pathophysiological and diagnostic questions.

Its most important advantages compared to other methods used at the time, such as the combustion methods by Jean-Baptiste Dumas and Anselme Payen and the method by Heinrich Will and Franz Varrentrapp called the Will-Varrentrapp method , proved to be robustness against disruptive influences as well as the low level Time required, which enabled a correspondingly high sample throughput . In addition, the Kjeldahl nitrogen determination is the reference standard in food analysis for determining the protein content up to the present. Routine analysis can now be carried out using appropriate technical equipment and ready-to-use reagents in automated form and with a correspondingly high degree of standardization.

In addition to the method developed by Johan Kjeldahl, the glass flask he designed for the digestion of organic materials as a Kjeldahl flask is named after him. His name has also entered scientific usage in the English-speaking world in the form to kjeldahl / kjeldahlize a sample or the sample was kjeldahled / kjeldahlized as a verb to describe the treatment of a sample according to his method. Analogous to this, the words Kjeldahlisierung or kjeldahlisierung are used as technical terms in German .

Awards

Johan Kjeldahl was admitted to the Royal Danish Academy of Sciences in 1890 and to the Norwegian Academy of Sciences in Christiania in 1892 , and in the same year he was appointed adjunct professor. The University of Copenhagen awarded him an honorary doctorate in 1894 , in addition he received the Knight's Cross of the Dannebrog Order (for the year of the award, see notes on literature).

Works (selection)

• Studies on carbohydrates in barley and malt, with special attention to the occurrence of cane sugar. In: Meddelelser fra Carlsberglaboratoriet. 1/1881. Pp. 339-379
• New method for the determination of nitrogen in organic bodies. In: Journal for Analytical Chemistry. 22 (1) / 1883. Pp. 366-382
• Investigations into the behavior of the sugar types towards copper solutions. In: Meddelelser fra Carlsberglaboratoriet. 4/1895. Pp. 1-62
• About the determination of the types of sugar. Wiesbaden 1896

literature

The article is based entirely on the literature listed below. The biographical information is based in particular on a retrospective by D. Thorburn Burns published on the occasion of the 100th anniversary of the publication of his method, as well as a résumé of Stig Veibel published on the 100th anniversary of his birthday, and was accompanied by entries in two contemporary lexical works ( Nordisk familjebok and Dansk biografisk lexicon ). The information about his scientific work comes mainly from the obituary published by Wilhelm Johannsen.

The exact cause of death while bathing in Tisvilde is mentioned in the obituary by Johannsen and in the Biographical Encyclopedia of Scientists as a heart attack, while in the review by Burns and in the article by Hugh A. McKenzie a stroke is given. The award of the Knight's Cross of the Dannebrog Order took place according to the obituary in 1892, according to the Burns article, however, in 1898. The Nordisk familjebok and the Dansk biografisk lexicon contain no further information on either aspect.

• Kjeldahl, Johan Gustav Christoffer Thorsager . In: Theodor Westrin (Ed.): Nordisk familjebok konversationslexikon och realencyklopedi . 2nd Edition. tape 14 : Kikarskten – Kroman . Nordisk familjeboks förlag, Stockholm 1911, Sp. 176 (Swedish, runeberg.org ).
• SM Jørgensen: Kjeldahl, Johan Gustav Christoffer Thorsager . In: Carl Frederik Bricka (Ed.): Dansk biografisk Lexikon. Tillige omfattende Norge for Tidsrummet 1537-1814. 1st edition. tape 9 : Jyde – Køtschau . Gyldendalske Boghandels Forlag, Copenhagen 1895, p. 190-191 (Danish, runeberg.org ).
• Wilhelm Johannsen: Johan Kjeldahl. Obituary in: Reports of the German Chemical Society. Issue 33 (3) / 1900. German Chemical Society, pp. 3881-3888
• Stig Veibel: John Kjeldahl (1849–1900). In: Journal of Chemical Education. 26 (9 )/1949. American Chemical Society, pp. 459-461, ISSN  0021-9584
• D. Thorburn Burns: Kjeldahl, the Man, the Method and the Carlsberg Laboratory. In: Analytical Proceedings. 21/1984. Royal Society of Chemistry, pp. 210-214, ISSN  0144-557X .
• Kjeldahl, Johan Gustav Christoffer Thorsager. In: John Daintith, Sarah Mitchell, Elizabeth Tootill, Derek Gjertsen: Biographical Encyclopedia of Scientists. Second edition. IOP Publishing, Bristol and Philadelphia 1994, ISBN 0-7503-0287-9 , Volume 1, pp. 488/489.
• Hugh A. McKenzie: The Kjeldahl Determination of Nitrogen: Retrospect and Prospect. In: Trends in Analytical Chemistry . 13 (4 )/1994. Elsevier, pp. 138–144, ISSN  0165-9936 (biographical information pp. 138/139; explanations on the discovery, further development and significance of Kjeldahl's nitrogen determination pp. 139–143).
• Kjeldahl Analysis. In: Louis Rosenfeld: Four Centuries of Clinical Chemistry. Gordon & Breach Science, Amsterdam 1999, ISBN 90-5699-645-2 , pp. 60-62.

Web links

Commons : Johan Kjeldahl  - collection of images, videos and audio files

• e-Learning for Quantitative Analysis: Kjeldahl Method. Illustrated description of Kjeldahl's nitrogen determination

This version was added to the list of articles worth reading on December 27, 2007 .