Kjeldahl determination of nitrogen

Figure 5-3 Absolute error in the micro-Kjeldahl determination of nitrogen. Each dot represents the error associated with a single determination.

Difficulties in the Kjeldahl determination of nitrogen (c), center chiefly on the problem of digestion. Variable factors known to influence the completeness (and speed) of conversion of protein nitrogen into ammonia by sulfuric acid digestion include the following sources of error ... 

Calcium cyclamate, Ci2H2406N2S2Ca,2H20, Mol. Wt. 432-6. This material is officially assayed in the U.S.P, by a Kjeldahl determination of nitrogen but it may be determined through its organic sulphur content,... 

Kjeldahl method An analytical method for the determination of nitrogen particularly in organic materials. The N is converted to NH with cone. H2SO4 and catalysts. After neutralization the NH j is distilled ofT and estimated by titration after absorption. 

Equipment for automated Kjeldahl determinations of organic nitrogen in water and solid samples is supplied by Tecator Ltd. Their Kjeltec system 1 streamlines the Kjeldahl procedure resulting in higher speed and accuracy compared to classical Kjeldahl measurements. 

A titrimetric method that has been used for many years for the determination of nitrogen or protein in a sample is the Kjeldahl method. Examples of samples include grain, protein supplements for animal feed, fertilizers, and food products. It is a method that often makes use of the back titration concept mentioned above. We will now describe this technique in detail. 

The determination of nitrogen in petroleum products is performed regularly by the Kjeldahl method (ASTM D3228), the Dumas method, and the microcoulomet-ric (ASTM D3431) method. The chemiluminescence method is the most recent technique applied to nibogen analysis for petroleum and is used to determine the amount of chemically bound nitrogen in liquid samples. 

The original method for the determination of nitrogen by sulphuric acid-digestion was published by Kjeldahl in 1883 and fully described by Burns (1984). Many modifications have since been made with various catalysts and acid mixtures. 

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. 

The standard procedure of nitrogen determination by many laboratories is the Kjeldahl method (ASTM D-3179 ISO 333), although there are the standard methods that involve the Dumas technique (DIN 51722) and the gasification procedure (DIN 15722). Neutron activation analysis has also been proposed for the determination of nitrogen in coal, coal ash, and related products (Volborth, 1979a). 

Nitrogen determination by perchloric acid digestion of coal without catalysts is reportedly safe and much more rapid than the conventional Kjeldahl procedure. Nitrogen is determined in the digest by the usual ammonia evolution and titration. However, extreme care should be taken whenever perchloric acid is used. Nuclear reactions have been applied successfully to the determination of nitrogen in coal. 

DIN 15722. Testing of Solid Fuels Determination of Nitrogen Content Dumas Method. DIN 51722. Testing of Solid Fuels Determination of Nitrogen Content Semi-Micro Kjeldahl Method. 

ISO 333. Determination of Nitrogen Semi-micro Kjeldahl Method. 

N. B. Kiriakidis, Determination of nitrogen by the Kjeldahl method , Chim. Chron. Genike Ekdose, 1996, 58, 401—404. 

Johan Kjeldahl first described his method for the determination of nitrogen in proteinaceous materials in 1883, when he was director of the Chemical Laboratory at the Carlsberg Foundation. At that time there was a pressing need for a more convenient and reliable procedure. Wanklyn s albuminoid ammonia method gave low and erratic results. Kjeldahl developed a succession of modifications that resulted in a technique very different from Wanklyn s - one which is still substantially the same today.65 66... 

Kjeldahl method for determination of nitrogen in organic compounds The... 

The authors found that the determination of nitrogen in PV.N in a nitrometer or by the Kjeldahl method did not give reliable results. It was ncccssar> to use the Dumas method. According to Diepold [25] the method of titration with Fe 11 also gives reliable results. 

Kjeldahl flask. A round bottom flask with a long wide neck that is used in the determination of nitrogen by Kjeldahl s method. 

Kjeldahl method A titration method for the determination of nitrogen in organic compounds in which the nitrogen is converted to ammonia, which is then distilled and determined by a neutralization titration. 

G.L. Miller, E.E. Miller, Determination of nitrogen in biological materials, improved Kjeldahl-Nessler method, Anal. Chem. 20 (1948) 481. 

The Kjeldahl method for the determination of nitrogen is the one generally used in the analysis of food-products and other complex mixtures. The substance to be analyzed is heated with concentrated sulphuric acid until it is completely oxidized. The nitrogen present is converted into ammonia, which unites with the excess of sulphuric acid to form ammonium sulphate. The amount of ammonia formed is determined by treating the mixture of the acid and ammonium salt with an excess of sodium... 

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