Sulfuric acid Kjeldahl method

Kjeldahl method analychem Quantitative analysis of organic compounds to determine nitrogen content by interaction with concentrated sulfuric acid ammonia Is distilled from the Nff4S04 formed. kel,dal, meth-ad )... 

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... 

M.I. Fauth H. Stalcup, AnalChem 30,1670— 72(1958) Be CA 53, 2929(1959) [Evaluation of six methods for detn of nitrogen in NGu. (Nitro N methods tested are modified nitrometer — greatest precision of the six acetate-buffered titanous chloride transnitration with sulfuric acid and Bowman-Scott). Total N methods are modified Kjeldahl and micro-Dumas — better of these two. The titanous chloride and trans-nitration methods are satisfactory]... 

KJELDAHL TEST. An analytical method for determination of nitrogen in certain organic compounds. It involves addition of a small amount of anhydrous potassium sulfate to the test compound, followed by healing the mixture with concentrated sulfuric acid, often with a catalyst such ns copper sulfate. As a result ammonia is formed. Alter alkaly/ing the mixture with sodium hydroxide, the ammonia is separated by distillation, collected in standard acid, and the nitrogen determined by back-iilruiion. 

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. 

Analysis. The heating value, ash content, and sulfur distribution of the raw and treated coals were determined according to ASTM procedures (7). Iron in the extracts of the raw and treated coals was determined by titration with a cerium (IV) solution. Iron in the residues from the acid extractions of the raw and treated coals was determined spectrophotometrically using ferrozine (20). The liquid extracts were analyzed for total sulfur (as sulfate) by ion chromatography after separation of the sulfate from nitrate on an alumina column (21). Nitrogen was determined in the raw and treated coal and in their nitric acid-extracted residues by a modified Kjeldahl method. 

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. 

An often used method for the detn of either aminoid or nitrate nitrogen is the decompn-volumetric Kjeldahl (or Chenel) procedure in which the sample is decompd with coned sulfuric acid and suitable catalyzers to yield amm sulfate quant. After release with strong alkali, the ammonia is quant distd into an excess of standard add and back-titrated with standard alkah (See Vol 1, A616-R Vol 2, C46-L ... 

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... 

In the Kjeldahl method, the sample is decomposed in hot, concentrated sulfuric acid to convert the bound nitrogen to ammonium ion. The resulting solution is then cooled, diluted, and made basic. The liberated ammonia is distilled, collected in an acidic solution, and determined by a neutralization titration. 

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 ... 

Protein was determined by the method of Lowry (7) after hydrolysis with 0.2N NaOH (100°C, 15 min). Total nitrogen was measured by the micro-Kjeldahl method with sulfuric acid/hydrogen peroxide reagentj the ammonia was detected with Nessler s reagent. Glucose was measured by standard colorimetric assay using dinitrosalicylic acid. Starch was hydrolyzed with concentrated HC1 and then determined as sugar. 

Cyanide is determined by a modified Kjeldahl method. A suitable sample is distilled with 125 ml. of 3 A sulfuric acid 100 ml. of the distillate is caught in a solution of 0.1 N sodium hydroxide, which is then titrated with standard silver nitrate solution. Potassium and chromium are determined on the same sample. The sample is decomposed with aqua regia, evaporated to diyness, and taken up with water, and chromium(III) hydroxide is precipitated by addition of ammonia. The filtrate is evaporated with sul-... 

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. 

Nitrogen is determined by the Kjeldahl method. Nitrogen is transformed in ammonium sulfate by treatment with concentrated sulfuric acid at 900°C. Afterwards it is liberated as ammonia in a steam stream that passes through a diluted acid solution and a titration with alkali (see ISO 332, ASTM D3179). 

Kjeldahl method Ammonia produced by the oxidation of the enzyme by concentrated sulfuric acid is measured using the indophenol technique 0.5-1 Opg ml" ... 

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