Nitrogen analysis, Kjeldahl procedure

Kjeldahl nitrogen analysis Procedure for the analysis of nitrogen in organic compounds. The compound is digested with boiling H2S04 to convert nitrogen into NHj", which is treated with base and distilled as NH into a standard acid solution. The moles of acid consumed equal the moles of NH3 liberated from the compound. 

For 15 N-measurements about 2 mg of pure uric acid were degraded by a modified Kjeldahl procedure and molecular nitrogen liberated for analysis of its isotope content by Li 0 Br (Ross and Martin, 1970) For 13 C-analysis uric acid was combusted according to Winkler and Schmidt (1980). Uric acid concentrations were measured enzymatically (Zailner, 1963). 

Kranz and co-workers [126] have shown that acrylonitrile can he determined in styrene - butadiene - acrylonitrile terpolymers via a determination of organic nitrogen by the Kjeldahl procedure. Styrene units can be can be determined by infrared spectroscopy. Butadiene units can be determined by the iodine monochloride procedure. The compositional analysis and details of the microstructure of butadiene - acrylonitrile copolymers can be obtained by Raman spectroscopy [127]. 

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]. 

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). 

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. 

Other major shale constituents such as C, H, N, and S are determined by thermal decomposition and instrumental detection methods. Oxygen is determined by 14 MeV neutron activation analysis. Parr or Leco BTU bomb combustion and subsequent ion chromatographic determination is used for halogens, sulfate and nitrate. Ion chromatography is also suitable for anionic characterization of shale process waters. Two analytical procedures for oil shales should be used with caution. Kjeldahl nitrogen procedure has been found to give reproducible but considerably low results for certain oil... 

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