Question: What is the titration invented by the Danish chemist famous for the concept of pH used for?

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Merle Randall: Merle Randall (January 29, 1888 – March 17, 1950) was an American physical chemist famous for his work with Gilbert N. Lewis, over a period of 25 years, in measuring reaction heat of chemical compounds and determining their corresponding free energy.  Together, their 1923 textbook ""Thermodynamics and the Free Energy of Chemical Substances"" became a classic work in the field of chemical thermodynamics.

Paul D. Boyer: Paul Delos Boyer (born July 31, 1918) is an American biochemist, analytical chemist, and a professor of chemistry at University of California Los Angeles (UCLA) .  He shared the 1997 Nobel Prize in Chemistry for research on the "enzymatic mechanism underlying the biosynthesis of adenosine triphosphate (ATP)" (ATP synthase) with John E. Walker, making Boyer the only Utah-born Nobel laureate; the remainder of the Prize in that year was awarded to Danish chemist Jens Christian Skou for his discovery of the Na+/K+-ATPase.  He is the oldest living Nobel laureate at age 99 .

Thomsen–Berthelot principle: In thermochemistry, the Thomsen–Berthelot principle is a hypothesis in the history of chemistry which argued that all chemical changes are accompanied by the production of heat and that processes which occur will be ones in which the most heat is produced.  This principle was formulated in slightly different versions by the Danish chemist Julius Thomsen in 1854 and by the French chemist Marcellin Berthelot in 1864.  This early postulate in classical thermochemistry became the controversial foundation of a research program that would last three decades.

Poul Bjørndahl Astrup: Poul Bjørndahl Astrup (4 August 1915 – 30 November 2000) was a Danish clinical chemist famous for inventing a CO electrode and co-inventing the concept of base excess.

Edward Asselbergs: Edward Anton Maria Asselbergs (1927–1996) was a Dutch-Canadian food chemist famous for inventing the modern process of producing instant mashed potato flakes.

Sørensen formol titration: The Sørensen formol titration(SFT) invented by S. P. L. Sørensen in 1907 is a titration of an amino acid with potassium hydroxide in the presence of formaldehyde.  It is used in the determination of protein content in samples.

Karl Fischer titration: Karl Fischer titration is a classic titration method in analytical chemistry that uses coulometric or volumetric titration to determine trace amounts of water in a sample.  It was invented in 1935 by the German chemist Karl Fischer.  Today, the titration is done with an automatized Karl Fischer titrator.

Bergnart Carl Lewy: Bergnart (Bernhard) Carl Lewy was a Danish chemist; born in Copenhagen on 5 July 1817.  He died there on 1 January 1863.  He obtained the degree of graduate of pharmacy in 1835, and then studied chemistry for three years at the polytechnic school.  In 1839 he studied in Berlin (Ph.D.), and spent the winter of 1839-40 in Rome.  He then obtained a position as assistant in the private laboratory of J. B. Dumas in Paris.

Karl Friedrich Mohr: Karl Friedrich Mohr (November 4, 1806 – September 28, 1879) was a German chemist famous for his early statement of the principle of the conservation of energy.  Ammonium iron(II) sulfate, (NH)Fe(SO).6HO, is named Mohr's salt after him.

S. P. L. Sørensen: Søren Peder Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and alkalinity.  He was born in Havrebjerg, Denmark.

Supporting paragraphs: Sørensen formol titration S. P. L. Sørensen
Answer: the determination of protein content