Johan Gustav Christoffer Thorsager Kjeldahl ( 16 August 1849 – 18 July 1900), was a

Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish a ...

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

who developed a method for determining the amount of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

in certain

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

s using a

laboratory technique A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physici ...

which was named the

Kjeldahl method The Kjeldahl method or Kjeldahl digestion () in analytical chemistry is a method for the quantitative determination of nitrogen contained in organic substances plus the nitrogen contained in the inorganic compounds ammonia and ammonium (NH3/NH4+) ...

after him.

Professional life

Kjeldahl worked in

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at the

Carlsberg Laboratory The Carlsberg Research Laboratory is a private scientific research center in Copenhagen, Denmark under the Carlsberg Group. It was founded in 1875 by J. C. Jacobsen, the founder of the Carlsberg brewery, with the purpose of advancing biochemica ...

, associated with

Carlsberg Brewery Carlsberg A/S (; ) is a Danish multinational brewer. Founded in 1847 by J. C. Jacobsen, the company's headquarters is in Copenhagen, Denmark. Since Jacobsen's death in 1887, the majority owner of the company has been the Carlsberg Foundation. T ...

, where he was head of the ''Chemistry department'' from 1876 to 1900. Carlsberg Laboratory

He was given the job to determine the amount of protein in the

grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

used in the

malt Malt is germinated cereal grain that has been dried in a process known as " malting". The grain is made to germinate by soaking in water and is then halted from germinating further by drying with hot air. Malted grain is used to make beer, wh ...

industry. Less

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

meant more

beer Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from ce ...

. Kjeldahl found the answer was in developing a technique to determine nitrogen with accuracy but existing methods in

analytical chemistry Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...

related to proteins and

biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...

at the time were far from accurate.

Kjeldahl method

In order to solve the problem of determining accurate nitrogen content in a sample, Kjeldahl developed a method which involves a two-step reaction: a

distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

and a

back titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...

. He found that

ammonium salt The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

s can be produced by the reaction between

s and

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

; this step is a

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

. Ammonium salts produced from this step were collected and, in a second process, reacted with

lye A lye is a metal hydroxide traditionally obtained by leaching wood ashes, or a strong alkali which is highly soluble in water producing caustic basic solutions. "Lye" most commonly refers to sodium hydroxide (NaOH), but historically has been u ...

. The ammonia produced in this step was distilled and dissolved in a standardized solution of

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

. Finally, this solution was back titrated with

caustic soda Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alka ...

to indirectly measure nitrogen. During the 1880s, Kjeldahl used

potassium sulfate Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the inorganic compound with formula K2SO4, a white water-soluble solid. It is commonly used in fertilizers, pro ...

to raise the boiling point of the acid and

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

as a catalyst to speed the decomposition. For the back titration process of the released ammonia, he used

boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolves ...

buffer solution A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is ...

. On 7 March 1883, Kjeldahl presented his method at the

Danish Chemical Society The Danish Chemical Society ( da, Kemisk Forening) was founded in 1879. The nonprofit organization aims to advance the chemical sciences in Denmark. By 1 November 2003, there were approximately 870 members. The revenue received from membership fees ...

Legacy

Johan Kjeldahl died on 18 July 1900 in

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Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...

at the age of 50.

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, 1900-07-19. His laboratory technique for nitrogen and protein analysis is still the universally accepted method for this analysis. Although other methods claim to be faster and more efficient, none can cope with the variety of sizes or conditions of samples than Johan Kjeldahl's original method. Kjeldahl equipment is used extensively all over the world.

Literature

*Jessen-Hansen, H. (1932) Johan Kjeldahl, pp. 169–172 in: Meisen, V. Prominent Danish Scientists through the Ages. University Library of Copenhagen 450th Anniversary. Levin & Munksgaard, Copenhagen.

References

{{DEFAULTSORT:Kjeldahl, Johan 1849 births 1900 deaths Danish chemists Carlsberg Laboratory staff