Determination of nitrogen

Nitrogen is determined by the classic Kjeldahl method, in which the nitrogen is converted to ammonium ions, distilled from an alkaline solution and determined by acid titration. Various catalysts have been used for the conversion to ammonium ions. The one suggested here works satisfactorily. 

Weigh a sample containing 0.02-0.03 g nitrogen and place it in the Kjeldahl flask. Liquids and pastes may be weighed into a small plastic 

Add five selenium catalyst tablets, 25 ml concentrated sulphuric acid (caution corrosive) and two or three glass beads. 

Set up a blank experiment in the same way but omitting the sample. If the sample was weighed in a capsule, include a similar capsule in the blank. 

Clamp both flasks with their necks inclined at about 45° and heat over low bunsen flames until fumes appear above the acid solution. Continue heating until the liquid becomes clear, then for a further 30 min. Heat the blank for the same time as the sample. Allow to cool. 

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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. 

Fig. XVII-5. Schematic detector response in a determination of nitrogen adsorption and desorption. A flow of He and N2 is passed through the sample until the detector reading is constant the sample is then cooled in a liquid nitrogen bath. For desorption, the bath is removed. (From Ref. 28. Reprinted with permission from John Wiley Sons, copyright 1995.)...

Phenol sulfonic acid (determination of nitrogen as nitrate water analysis for nitrate) dissolve 25 g pure, white phenol in 150 mL of pure concentrated H2SO4, add 75 mL of fuming H2SO4 (15% SO3), stir well and heat for two hours at 100°C. 

U.S. EPA, Method SCI-Determination of Nitrogen- and Phosphorus Containing Pesticides in Ground Water hy GCj NPD, draft, Apr. 15, 1988 available from U.S. EPA Environmental Monitoring and Support Laboratory, Cincinnati, Ohio, 1988. 

B. Langfoid and I. H. Stice, The Determination of Nitrogen and Oxygen by Inert Gas Fusion, Teledyne Wab Chang Corp., Albany, Oieg., 1994. 

Determination of Nitrogen by FP-228 Organic Nitrogen Terminator, LECO Corp., St. Joseph, Mich., 1985. 

If chloride is present, saturated aqueous silver acetate solution should be added in amounts slightly more than the calculated quantity prior t o the addition of concentrated sulphuric acid. The procedure may be applied to the routine analysis of mixtures of nitric and sulphuric acids, and to the determination of nitrogen in esters such as nitroglycerine and nitrocellulose the latter are easily hydrolysed by strong sulphuric acid after dispersal in glacial acetic acid. 

Carter et al, Modified Devarda Method for the Determination of Nitrogen in Nitrocellulose ,... 

Cellulose Chemistry , London (1947), 245—47 22) B.T. Fedoroff, Rapid Method for the Determination of Nitrogen Content of Nitrocellulose by the Ferrous Ammonium Sulphate Method , PACLR 122871 (1948) 23) J. Pearson... 

Detn of N in NC by the Nitron method and comparison of results with those obtained by nitrometer] 5) W.C. Cope G.B. Taylor, The Determination of Nitrogen in Substances Used in Explosives , USBurMines, Tech Paper 160, Washington, DC (1917), 18-20... 

Mariotti, A., Germon, J.C., Hubert, P., Kaiser, R, Letolle, R., Tardieux, A. and Tardieux, P. 1981 Experimental determination of nitrogen kinetic isotope fractionation some principles illustration for the denitrification and nitrification processes. Plant and Soil 62 413-430. 

Another analytic procedure based on HPLC has been developed for the quantitative determination of nitrogen-containing corrosion inhibitors [1194]. The method was primarily developed for the analysis of certain oil pipeline condensate samples. 

Some methods were proposed for the determination of nitrogen oxides based on the reaction with ozone [128, 129] ... 

There is one case where total destruction of soil organic matter and its constituents is standard practice and that is in the determination of nitrogen... 

The effect of storage of water samples before determination of nitrogen and carbon associated with particulate matter was investigated. Freezing of the samples, and storage at 5°C, both affected the results obtained, but changes were minimized if the samples were filtered immediately after collection and the particulate matter stored on the filter paper. It is recommended that samples for determination of particulate carbon and nitrogen should be filtered immediately, and analysed as soon as possible. 

Pelts and Belcher [46] have described a semi-automated method for the simultaneous determination of nitrogen and phosphorus in soil. Up to 40 samples are digested with sulphuric acid using a copper sulphate-sodium sulphate catalyst at 370°C for 2.25h in a thermostatically controlled block. Nitrogen is then determined in the 0.2-2.25% range as ammonia by automatic colorimetric analyses of the indophenol blue complex at 630nm. 

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 the pure product was performed by the usual method of slow distillation with excess of dilute sodium hydroxide solution, the evolved ammonia being collected, during 4 hr. distillation, in standard acid, and determined by titration as usual, with methyl orange as indicator. The yield of ammonia corresponded to 18-19 per cent of nitrogen in this sample. Calculated for FCH2CONH, N= 18-18 per cent. The standard fiuoroacetamide was therefore 100 per cent pure. 

TABLE FOR CALCULATIONS IN THE DETERMINATION OF NITROGEN BY DUMAS METHOD... 

Collect the eluate in fractions of about 4 ml and combine the fractions corresponding to each peak. For each combined fraction carry out the determination of nitrogen as per BP (1993). Not more than 10% of the total nitrogen is present in the combined fraction associated with non-retained proteins. 

Edgell KW, Jenkins EL, Lopez-Avila V, et al. 1991. Capillary column gas chromatography with nitrogen-phosphorus detection for determination of nitrogen- and phosphorus-containing pesticides in finished drinking waters Collaborative study. J Assoc Off Anal Chem 74 295-309. 

For the determination of nitrogen- and phosphorus-containing pesticides in water by extraction with dichloromethane and detection by GC-NPD... 

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. 

Dumas method analychem A procedure for the determination of nitrogen in organic substances by combustion of the substance. dti-ma. meth-od dunnite See ammonium picrate. da.nTt)... 

Determination of Nitrogen- and Phosphorus-Containing Pesticides in Water by GC with a Nitrogen-Phosphorus... 

Nitrate ISEs can also be used for determination of nitrogen oxides after oxidation to the pentavalent form (for example with H2O2) [39, 41, 101, 109, 150]. The nitrate ISE system is also useful for 2,4-dichlorophenoxyacetate [73] and for tetrathionate [215]. 

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