Reduction of nitrate

Qualitative Analysis. Nitric acid may be detected by the classical brown-ring test, the copper-turnings test, the reduction of nitrate to ammonia by active metal or alloy, or the nitrogen precipitation test. Nitrous acid or nitrites interfere with most of these tests, but such interference may be eliminated by acidifying with sulfuric acid, adding ammonium sulfate crystals, and evaporating to alow volume. 

Nitrate and Nitrite. Nitrate is usually present in trace quantities in surface waters but occasionally occurs in high concentrations in some groundwaters. If present in excessive amounts, it can contribute to the illness infant methemoglobinemia. Nitrate is an essential nutrient for many photosynthetic autotrophs. Nitrite is an intermediate in the reduction of nitrate as well as in the oxidation of ammonia it is also used as a corrosion inhibitor in some industrial processes. 

Nitrous oxide may also be obtained by the controlled reduction of nitrates or nitrites, decomposition of hyponitrites, or thermal decomposition of hydroxylamine. 

Chemical reduction of nitrates has also been employed ... 

Nitrites are usually obtained by the mild reduction of nitrates, using C, Fe or Pb at moderately elevated temperatures, e.g. ... 

This enzyme is of wide occurrence in bacteria where it is concerned with the reduction of nitrate and CO2 as well as sulphur. Methods for its estimation depend on measuring some activity of hydrogenase by (a) dye reduction (benzyl viologen or methylene blue), (b) isotopic exchange and (c) evolution of molecular hydrogen. Interpretation of quantitative results is difficult due to the complex relationship between the enzyme cell structure and the particular method selected. ... 

Nitrites are the salts of nitrous acid, discovered by Scheele in 1774. The inorganic nitrites, with die general formula M.N02, where M is a metal, are well known. They are all insol in w with the exception of the alkali nitrites. Nitrites may be prepd either by thermal decompn of alkali nitrates 2KN03 2KNOJ + 02 or by reduction of nitrates by C or Pb 2KN03 + C 2KN02 + C02. The lone pair of electrons in the nitrite ion is sterically significant consequently, the nitrite ion is bent ... 

There are two important hydrogenation (or reduction) — titration procedures for the detn of N as ammonia. The Devarda method involves the quant reduction of nitrates to ammonia in alkaline soln using an Ai-Cu-Zn alloy. The ammonia evolved is distd into standard sulfuric acid... 

Nitrous acid, the parent acid of the nitrites, has not been isolated in pure form but is widely used in aqueous solution. Nitrites are produced by the reduction of nitrates with hot metal ... 

Re(V) reduction of nitrate in 10 M hydrochloric acid to give nitrite and ReO is rapid and is followed by a slower reaction of Re(V) with NOJ of stoichiometry... 

The Fe(II) reduction of nitrate displays a nitrogen isotope effect of... 

Bacteria have been Implicated in the formation of N-nitroso compounds under a wide variety of conditions representing both vitro and vivo situations Mechanisms of participation and/or catalysis Include a) decrease of the pH of the system, b) reduction of nitrate to nitrite, c) adsorption of amine onto the cell surface or cytoplasmic membrane, d) actual enzymatic formation. The literature of the field will be reviewed and experimental evidence which tests the above mechanisms will be presented ... 

We conclude that the major role of bacteria in the nitrosa-tion of dimethylamine is the reduction of nitrate to nitrite and the lowering of the pH of the medium. Furthermore, the complex medium Itself catalyzes nitrosation. The nature of this catalysis is not known, although it could be due to the presence of carbonyl compounds, cysteine, or a variety of other compounds which are known to catalyze nitrosation (17). 

N-Nitrosamines, formed principally from the reaction of naturally occurring secondary amines with nitrites that may be added to foods or produced by bacterial reduction of nitrates, have been identified in many food systems including cured meat products, nonfat dried milk, dried malt and beer. In addition, the presence of less volatile and non-volatile N-nitroso compounds or their precursors in foods have been suggested from a number of model system studies. 

The nitrite results from reduction of nitrate by bacteria abnormally present in the gastric mucosa and the gastric cavity. The bacteria grow situ because the pH is elevated as a result of loss of HCl secretion secondary to the loss of parietal cells and their replacement by intestinal-type epithelium. Parietal cells are lost as a result of chronic atrophic gastritis. What... 

Bacteria have been isolated using reduced anthraquinone-2,6-disulfonate (HjAQDS) as electron donor and nitrate as electron acceptor (Coates et al. 2002). The organisms belonged to the a-, p-, y-, and 5-subdivision of the Proteobacteria, and were able to couple the oxidation of H AQDS to the reduction of nitrate with acetate as the carbon source. In addition, a number of C2 and C3 substrates could be used including propionate, butyrate, fumarate, lactate, citrate, and pyruvate. 

Ridley H, CA Watts, DJ Richardson, CS Butler (2006) Resolution of distinct membrane-bound enzymes from Enterobacter cloacae SKLDla-1 that are responsible for selective reduction of nitrate and selenate anions. Appl Environ Microbiol 12 5173-5180. 

Hence, TPD and TPSR data obtained over the binary catalyst showed that the presence of a net reducing environment did not play any significant role in the decomposi-tion/reduction of nitrates stored over Ba. Indeed a partial reduction of stored NO could... 

Complex (21), a Con-cyclam analogue, is very active for the reduction of N02 and NH2OH intermediates and catalyzes the complex electrochemical conversion of N03 to NH3 325 Gold electrodes modified with cobalt-cyclam incorporated in Nafion films,324 or by electropolymerization of the pyrrole-substituted cobalt cyclam (22)326 have shown catalytic activity for the reduction of nitrate in strongly basic media. 

Reduction of nitrates or nitrites by sodium amalgam in the presence of water has been used to prepare salts of hyponitrous acid. 

Sigman et al. [134] have described a bacterial method for measuring the isotopic composition of seawater nitrate at the natural-abundance level. The method is based on the analysis of nitrous oxide gas (N2O) produced quantitatively from nitrate by denitrifying bacteria. The classical denitrification pathway consists of the stepwise reduction of nitrate (NOp to nitrite (N02), nitric oxide (NO), nitrous oxide (N2O), and dinitrogen (N2) ... 

Bajic and Jaselskis [153] described a spectrophotometric method for the determination of nitrate and nitrite in seawater. It included the reduction of nitrate and nitrite to hydroxylamine by the zinc amalgam reactor (Jones reductor) at pH 3.4 and reoxidation of the product with iron (III) in the presence of ferrozine. Interference by high levels of nitrite could be eliminated with azide treatment. Levels of nitrate of 0.1 mg/1 could be detected with a precision of 3% in the presence of large amounts of nitrite and chloride. 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

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