Sulfuric acid Kjeldahl digestions

Kjeldahl Method. A method of detg the N in an organic compd by digesting the substance with coned sulfuric acid in the presence of catalysts such as selenium, Devarda s alloy, etc. This treatment transforms the N into Amm sulfate. By adding an excess of caustic and distg the liberated ammonia into a measured quantity of standard sulfuric acid (which is later titrated), it is possible to determine the amount of N in the substance... 

In the Kjeldahl method, pulverized coal is boiled coal with concentrated sulfuric acid containing potassium sulfate and a suitable catalyst to reduce the time for digestion. The catalyst is usually a mercury salt, selenium itself, or a selenium compound, or a mixture of the two. Selenium is regarded as being particularly advantageous. 

Nitrogen in organosilicon compounds can be determined by the standard Kjeldahl method. Both silicon and nitrogen can be determined on the same sample by digesting it in concentrated sulfuric acid to which a drop of mercury has been added 18 the silica is filtered from the diluted acid, and ammonia is distilled from the filtrate after alkali sulfide and caustic solution have been added. The distilled ammonia is absorbed in standard acid, and the excess of acid is titrated in the usual manner. 

In the Kjeldahl method, the organic compound is digested with concentrated sulfuric acid, which converts combined nitrogen into ammonium sulfate. The solution is then made alkaline. The ammonia thus liberated is distilled, and its amount is determined by titration with standard acid. For example, the ammonia... 

Kjeldahl flask A long-necked flask used for the digestion of samples with hot. concentrated sulfuric acid. 

The Kjeldahl nitrogen method is based on the fact that, upon digestion with sulfuric acid and catalysts, the organic material is destroyed and most forms of nitrogen are converted to ammonia. When the digestion mixture is made alkaline, the ammonia is released. The ammonia is removed by distillation, absorbed, and titrated. These reactions can be represented as follows ... 

A protein sample is analyzed by digesting it with sulfuric acid to convert protein nitrogen to ammonium sulfate (Kjeldahl digestion). The digested sample is diluted to 100.0 ml,... 

Methods of Analysis.—Analyses for nitrogen were made by the semimicro Kjeldahl method, using the apparatus described by Redemann. Sulfuric acid, copper sulfete, and potassium sulfate were used in the digestion mixture hydrogen peroxide was found not to be needed. 

The Kjeldahl digestion method is used to determine only the ammonia nitrogen content. Sodium hydroxide or magnesium oxide is used to raise the pH to above 12 to liberate the ammonia upon distillation, which is collected in a known amount of sulfuric acid. The excess sulfuric acid is titrated with sodium hydroxide and the percentage ammonia nitrogen is determined. Only ammonia-based fertilizer material should be analyzed using this method. 

Kjeldahl nitrogen is the classical assay for crude protein in meat, consisting essentially of a catalyst-aided (sulfate salts and copper or mercury) digestion with concentrated sulfuric acid at elevated... 

In the classical Kjeldahl method, the proteins are digested (wet oxidized) in sulfuric acid with a catalyst (mercury and selenium tablets now succeed by the much safer potassium and copper sulfate tablets). An acid solution of ammonium sulfate is formed which is then diluted in water. The solution is made alkaline with sodium hydroxide and heated to distil off ammonia into excess standard acid sulfuric acid. The excess acid is back-titrated with standard sodium hydroxide to determine the amount of ammonia. It is more usual now to use boric acid in which to collect the ammonia and titrate with standard hydrochloric acid. The Kjeldahl procedure has been partially automated in systems such as the Kjeltec Analyzer. Total protein can be calculated as nitrogen content x 6.38. 

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