Kjeldahl Method for Nitrogen

Magnesium nitride MgsNa + 6H2O 3Mg(OH)2 + 2NH3 Kjeldahl method for nitrogen Methanol and compounds that release ammonia, range 1% water... 

A satisfactorj method for treatment of organic arsenic consists in digestion with sulfuric acid (in the presence of starch) by analogj to the Kjeldahl method for nitrogen. Qualitatively the arsenic may be detected as sulfide and quantitatively by iodimetric methods. (J. Chem. Soc. 100, 1356 (1916 ). The Marsh test ser es for the detection of traces of arsenic. 

The Kjeldahl method for nitrogen determination is a good example of a back titration. The sample (for example, a food product) is oxidized by concentrated sulfuric acid to remove carbonaceous matter. Excess sodium hydroxide solution is then added, and the ammonia released is carefully distilled off into a known volume of standard acid, such as 0.1 M boric acid. The excess acid is then titrated with standard alkali. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

Bradstreet, R. B. The Kjeldahl Method for organic Nitrogen. New York London Academic Press 1965. 

Bradstreet, R. B. "The Kjeldahl Method for Organic Nitrogen," Academic Press, New York, 1965 p. 200. 

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

The classical method for nitrogen determination is the Kjeldahl procedure. The method is very precise and well... 

Bradstreet RB (1965) The Kjeldahl Method for Organic Nitrogen. Academic Press. 

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... 

In the early studies of ammonium fixation there was much uncertainty as to the amount of fixed ammonium present in untreated soils. The capacity of the soil for fixing ammonium could be determined readily by the methods already mentioned, but such techniques furnished no information on the amount of fixed ammonium present initially. Since surface soils usually fixed less ammonium than did subsoils, it seemed likely that this was because the surface soils already contained fixed ammonium, and also potassium. Determination of naturally-occurring fixed ammonium was difficult because it was not known if the Kjeldahl method for total nitrogen actually accounted for all of the fixed... 

O—H, and N—H. These bands enable the quantitative characterization of polymers, chemicals, foods, and agricultural products for analytes such as water, fatty acids, proteins, and the like. In many cases, the use of NIR reflectance spectroscopy has been able to replace time consuming, classical wet chemical analyses, such as the Kjeldahl method for protein nitrogen and the Karl Fischer titration for water content. The NIR region has been used for qualitative studies of hydrogen bonding, complexation in organometallic compounds, and solute-solvent interactions because the NIR absorptions are sensitive to intermolecular forces. 

Proteins in foods can be measured by NIR reflectance spectrometry with no sample preparation. This has replaced the standard Kjeldahl protein nitrogen determination, which required extensive sample preparation to convert protein nitrogen to ammonia, distillation of the released ammonia, and subsequent titration of the ammonia. The replacement of the Kjeldahl method for routine analysis by NIR has permitted online measurement of protein in food and beverage products. The Kjeldahl method is required for assaying the materials used to calibrate the NIR and for method validation. 

Skepticism People don t trust NIR (yet). Management still tends to adhere to the tried and trusted methods, such as forms of the Kjeldahl test for nitrogen or protein. Even the extremely efficient Dumas (combustion) method for nitrogen has been slow in widespread adoption, although in good hands it is more efficient and precise than any Kjeldahl method. 

Daun, J.K. and DeClercq, D.R. 1994. Comparison of combustion and Kjeldahl methods for determination of nitrogen in oilseeds. JAOCS, 71(10), 1069-1072. 

Analysis methods for nitrogen in nickel have been examined within BCR on cast metal (36). Although the nitrogen content in the sample was low (about 1 >g/g) an acceptable agreement was found between photon activation analysis, charged particle activation analysis, the Kjeldahl method and reducing fusion (Table VI-14). With the latter method some discrepancies were however noted low results (a) could be explained by too low extraction temperatures. A study carried out using photon activation showed that a temperature of 2000"C or more is recommended (see 3.3.1.1). 

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. 

The two chief methods for estimating nitrogen in organic compounds are (i) the Dumas method, which can be applied to all organic compounds (ii) the Kjeldahl method, which is of more restricted application, but which is frequently used in biochemical and physiological work. Its limitations are indicated in the description of the method (p. 492). 

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