Nitrogen, determination Kjeldahl method

On average, the Kjeldahl nitrogen determination method takes about 2 to 3 hr to complete... 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

Possible hazards introduced by variations in experimental techniques in Kjeldahl nitrogen determination were discussed [1]. Modem variations involving use of improved catalysts and hydrogen peroxide to increase reaction rates, and of automated methods, have considerably improved safety aspects [2], An anecdote is given of the classic technique when sodium hydroxide was to be added to the sulphuric acid digestion and was allowed to trickle down the wall of the flask. It layered over the sulphuric acid. Gentle mixing then provoked rapid reaction and a steam explosion [3],... 

The Kjeldahl total nitrogen determination method is not very sensitive, hut it suits well for analyzing insoluble samples without preceding disintegration. Automated Kjeldahl protein estimations are used especially in food analysis. 

Total nitrogen determinations in barley and malt gave slightly higher results by the Dumas than by the Kjeldahl method. The Dumas method was adopted as the reference method by the Analysis Committee of the Institute of Brewing27. Comparison of the results obtained by the Kjeldahl method with those of automatic N analyzers is mentioned in Section III.A.2 above. 

The whole column, apart from a small portion of the sediment, is sam pled in this way. The chemical checks were carried out every 15 days, determining pH, Conductivity, C.O.D., Ammoniacal Nitrogen, Orthophosphate Phosphorus and, furthermore, each month Total phosphorus, Total Kjeldahl Nitrogen, Total Solids and Volatile Solids. The methods utilized are those indicated in the Standard Methods (A.P.H.A., 1980). The amount of matter particles sedimented in the tanks was estimated with the use ol appropriate sampling devices located at the bottom of the tanks and withdrawn after a variable permanence of 40 to 60 days. 

Total and nitrate nitrogen were determined by Kjeldahl and colorimetric methods, respectively (29,30). Organic matter was determined by the wet oxidation method of Walkley (31). Soil pH was determined with a glass electrode in a 2 1 mixture of water and soil. 

We will describe the autoanalysis method based on Faithfull (1971a) which uses the same Kjeldahl acid digest solution as that used for the nitrogen determination (see Discussion 7.7). The proper development of the yellow colour of the phosphovanadomolybdate complex is sensitive to the pH,... 

Protein solubilities of soy flour and extrudates in the following solvent systems were determined by the micro-Kjeldahl method ( 9). A portion (0.1 g) of finely-ground sample (No. 60 sieve) was extracted with 9.9 ml of solvent for 1 hr at room temperature followed by centrifugation and filtration. An aliquot of the supernatant was used for nitrogen determination. 

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. 

Basic Protocol 1 Nitrogen Determination Using the Kjeldahl Method Bl.2.1... 

Measurements on a-Methylstyrene—Acrylonitrile. Polymerizations were carried out in dilatometers without solvent. Initiator was azobis-isobutyronitrile. At 100 °C the reaction was initiated thermally. At 0° and 20 °C the reaction was carried out in flasks in a thermally controlled room. Yields were below 5%. The composition of the copolymers was calculated from nitrogen determination (Kjeldahl method). In an older reference (29) polymerizations were carried out at 20°, 50°, 60°, and... 

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). 

The Kjeldahl-Gunning macro method is the one most widely used for determining nitrogen (ASTM D-3179). By this method, any nitrogen present in the... 

International Standard Organization. 1984. Water quality. Determination of Kjeldahl nitrogen. Method after mineralization with selenium. ISO 5663. International Organization for Standardization, Case Postale 56, CH-1211, Geneva 20 Switzerland. 

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