Johan Kjeldahl
Johan G. C. T. Kjeldahl (1849-1900), was a Danish chemist who developed the Kjeldahl method for determining nitrogen in certain organic compounds using sulfuric acid, potassium sulfate, and a catalyst (often cupric sulfate), to convert the nitrogen to ammonia which is distilled off and measured. Kjeldahl worked in Copenhagen at the Carlsberg Laboratory, associated with Carlsberg Brewery where he was head of the Chemistry department from 1876 to 1900. He needed to determine the amount of protein in the grain used in making the beer. Less protein meant more beer. Kjeldahl used hot sulfuric acid to digest the grain with the addition of a salt (potassium sulfate) to raise the boiling point of the acid and a cataylst to speed the decompostion. Kjeldahl used mercury as a catalyst. Sodium hydroxide is used to neutralize the solution which is distilled in to a boric acid buffer solution. The buffer solution was titrated back to its starting point to yield a measure of the released ammonia. On March 7, 1883, Kjeldahl presented his method at the Danish Chemical Society. This method with an updated catalyst and higher temperatures is still in widespread use more than a hundred years later.
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