Nitrate test

For the test to determine the ability of microbes to reduce nitrate to nitrite, see Nitrate reductase test.

A nitrate test is a chemical test used to determine the presence of nitrate ion in solution. Testing for the presence of nitrate via wet chemistry is generally difficult compared with testing for other anions, as almost all nitrates are soluble in water. In contrast, many common ions give insoluble salts, e.g. halides precipitate with silver, and sulfates precipitate with barium.

The nitrate anion is an oxidizer, and many tests for the nitrate anion are based on this property. Unfortunately, other oxidants present in the analyte may interfere and give erroneous results.

Brown ring test

A common nitrate test, known as the brown ring test^[1] can be performed by adding iron(II) sulfate to a solution of a nitrate, then slowly adding concentrated sulfuric acid such that the sulfuric acid forms a layer above the aqueous solution. A brown ring will form at the junction of the two layers, indicating the presence of the nitrate ion.^[2] Note that the presence of nitrite ions will interfere with this test.^[3]

The overall reaction is the reduction of the nitrate ion by iron(II) which is oxidised to iron(III) and formation of a nitrosyl complex.

NO₃^- + 3Fe²⁺ + 4H⁺ → 3Fe³⁺ + NO + 2H₂O

[Fe(H₂O)₆]²⁺ + NO → [Fe(H₂O)₅(NO)]²⁺

It should be noted here that Fe is not in its usual +2 oxidation state but is in a +1 Oxidation state and the NO is also in a +1 oxidation state.

Devarda's test

Main article: Devarda's alloy

Devarda's alloy (Cu/Al/Zn) is a reducing agent. When reacted with nitrate in sodium hydroxide solution, ammonia is liberated. The ammonia formed may be detected by its characteristic odor, and by moist red litmus — very few gases other than ammonia evolved from wet chemistry are alkaline.

3 NO−
3 + 8 Al + 5 OH⁻ + 18 H₂O → 3 NH₃ + 8 [Al(OH)₄]⁻

Aluminium is the reductant in this reaction.

Diphenylamine test

Diphenylamine may be used as a wet chemical test for the presence of the nitrate ion. In this test, a solution of diphenylamine and ammonium chloride in sulfuric acid is used. In the presence of nitrates, diphenylamine is oxidized, giving a blue coloration. This reaction has been used to test for organic nitrates as well,^[4] and has found use in gunshot residue kits detecting nitroglycerine and nitrocellulose.^[5]

Other oxidants such as chlorate, bromate, etc. interfere by similarly oxidizing diphenylamine. They may be removed by reduction with sodium sulfite. Where nitrite is present, a false negative result may be observed due to sulfite reducing nitrate in the presence of nitrite.

The diphenylamine test may be selective for nitrate by reducing nitrite with sodium azide, prior to treatment with sodium sulfite.^[6] Other derivatives have been reported as well.^[7]

See also

• Nitrite test

References

1. ^ Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
2. ^ Mascetta, Joseph A. Barron's How to Prepare for the SAT II: Chemistry, 7th edition. Barron's Educational Series, Inc., 2002. p208.
3. ^ Holltzclaw, H; Robinson, W. College Chemistry with qualitative analysis, 8th edition, D. C. Heath and Company:Lexington, MA, 1988, p. 1007.
4. ^ http://nvl.nist.gov/pub/nistpubs/jres/049/3/V49.N03.A05.pdf
5. ^ Pamela K. Walker and Philip J. Rodacy (2002). Field Test Kit for Gunshot Residue Detection. Sandia National Laboratories. http://prod.sandia.gov/techlib/access-control.cgi/2001/013942.pdf. 
6. ^ Suter, Hans A.; Suter, Patricia H. (1956). "A selective spot test for nitrate ion". Microchimica Acta 44 (7–8): 1136. doi:10.1007/BF01257445. 
7. ^ e.g. http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=36&issue=4&startPage=652

This article about analytical chemistry is a stub. You can help Wikipedia by expanding it.v · Categories: Chemical tests Analytical chemistry stubs Wikimedia Foundation. 2010. Игры ⚽ Поможем написать реферат Robert C. Byrd High School China National Nuclear Corporation Look at other dictionaries: dermal nitrate test —    An obsolete and unreliable test to determine if a person has fired a firearm. The test consists of treating paraffin casts taken of a person’s hands with diphenylamine which is a reagent that reacts positively with most oxidizing agents …   Forensic science glossary Nitrate reductase test — The nitrate reductase test is a test to differentiate between bacteria based on their ability or inability to reduce nitrate (NO3−) to nitrite (NO2−) using anaerobic respiration. Procedure Various assays for detecting nitrate reduction have been… …   Wikipedia test — 1. To prove; to try a substance; to determine the chemical nature of a substance by means of reagents. 2. A method of examination, as to determine the presence or absence of a definite disease or of some substance in any of the fluids, tissues,… …   Medical dictionary nitrate reduction test — (for bacteriuria or presence of bacteria in other fluids) a type of nitrite test that identifies the reduction of nitrate to nitrite by a bacterial culture. The fluid under investigation is cultured in a broth containing nitrate and the medium is …   Medical dictionary nitrate poisoning — although nitrate is less poisonous to fish than ammonia and nitrites (see nitrogen cycle), in high concentrations it is harmful and may also indicate the presence of other toxic waste products (most aquarium test kits measure ammonia, nitrites… …   Dictionary of ichthyology nitrate reductase — ni·trate re·duc·tase (niґtrāt re dukґtās) any of several enzymes occurring in plants and some bacteria and catalyzing the reduction of nitrate to nitrite. The reaction allows plants to use the nitrogen from nitrate for protein synthesis …   Medical dictionary Test du miroir d'argent — Réaction de Tollens La réaction de Tollens est une réaction caractéristique des aldéhydes. Ceci du fait des propriétés réductrices des aldéhydes, que n ont pas les cétones. Réactif de Tollens Pour l essentiel la solution de Tollens est un… …   Wikipédia en Français Nitrite test — A nitrite test is a chemical test used to determine the presence of nitrite ion in solution. A common nitrite test can be performed by adding 4 M sulfuric acid to the sample until acidic, and then adding 0.1 M iron(II) sulfate to the solution. A… …   Wikipedia Recherche de la nitrate reductase — Recherche de la nitrate réductase La nitrate réductase est une enzyme (un complexe enzymatique en réalité) qui est capable de catalyser la réaction de réduction des nitrates ( ). Sommaire 1 Principe 2 Mise en évidence 2.1 …   Wikipédia en Français Urea nitrate — Chembox new ImageFile = Urea nitrate.png ImageSize = IUPACName = OtherNames = Section1 = Chembox Identifiers CASNo = PubChem = SMILES = Section2 = Chembox Properties Formula = CH5N3O4 MolarMass = 123.068 g/mol Appearance = Density = MeltingPt =… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”