Nitrogen, determination

The 5-nitrofurfurylidene hydrazide of 4-hydroxybenzoic acid obtained was washed with water and methanol end was dried at a moderate temperature. It weighed 23 g (83.7% yield), and melted at 298°C. The percentage nitrogen determined by the micro-Dumas method was 15.41% (theory 15.27%). 

Another extremely important application area for FNA and RFNA is to either directly nitrate or be used in mixed acids to nitrate raw materials to yield widely used expls and proplnt ingredients (Refs 29,31,33,38 39). Also see under Nitration in this Vol Analytical. Analysis and assay procedures for nitric acid may be found in Refs 1, 2,10,11,15, 17, 27, 29, 34, 35, and in this Vol under Nitrogen Determinations in Energetic Materials. 

L34-R to L44-R Hypergolic Propellants in Vol 7, H254-L to H259-R Nitrogen Determination in Energetic Materials, and Mass Spectrometry in this Vol... 

Nonaqueous Titration Methods. See under Nitrogen Determination in Energetic Materials in this Vol... 

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]. 

Association Franjaise de Normalisation, Kjeldahl Nitrogen Determination with Microwave Sample Preparation, Rept NF V03-100 (1992). 

Nitrogen determination indicates a purity of 99.5 per cent. The product remains colorless for at least one year if... 

Kjeldahl digestion, 22 88 Kjeldahl nitrogen determinations, for paper, 18 99... 

Marsh et al. [47] have described an apparatus based on an autoanalyser system for the automatic preparation of soil extracts for mineral nitrogen determination. It consists of a reagent adder, which adds the correct volume of extractant for an approximately weighed amount of soil, and a sample preparation unit, which mixes, filters, dilutes and loads samples on to an autoanalyser sampler. A labour saving of 60% is achieved in this method compared to manual method. Examples are given of the determination of nitrate plus nitrate nitrogen and ammonium nitrogen. 

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. 

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],... 

Hedges, J.I., and J.H. Stem 1984. Carbon and nitrogen determinations of carbonate-containing solids. Limnology and Oceanography 29(3) 657-663. 

A procedure given by Zahn and Wiirz (89) was followed. 0.5 gm of the carbon was agitated with 25 ml of a 1 if solution of DNFB in dimethyl-formamide (DMF) for 20 hours. In order to neutralize the HF set free, 10 ml of a 1% aqueous solution of NaHCOj were added. The reaction products were washed and extracted successively with DMF, dilute HCl, methanol, and ether. Nitrogen determinations, Kjeldahl as well as Dumas determinations, gave identical results. Treatment with p-nitrobenzoylchloride followed standard procedures. 

Attempts were made in my laboratory to determine carbonyl groups with various carbonyl reagents, e.g., hydroxylamine, semicarbazide or dinitrophenylhydrazine. With hydroxylamine, oximes were formed to an extent that was equivalent to the difference between NaOEt and NaOH consumption. Errors due to binding of hydroxylammonium ions, which would show up in nitrogen determinations as well, were prevented either by methylation of the acidic groups with diazomethane or by ion exchange with dilute sodium hydroxide oximes are stable towards dilute alkali. However, only half the quantity of carbonyl groups reacted with semicarbazide or with dinitrophenylhydrazine. 

Robotic automation of total nitrogen determination by chemiluminescence 184... 

ROBOTIC AUTOMATION OF TOTAL NITROGEN DETERMINATION BY CHEMILUMINESCENCE... 

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,... 

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. 

Polymerization was carried out in CH2CI2 under nitrogen. Determined by H NMR analysis of the reaction mixture. Estimated by GPC based on polystyrene standards [ 14]. 

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