Nitrate is a

polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

Salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...

containing this

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conv ...

are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

in water. An example of an insoluble nitrate is

bismuth oxynitrate Bismuth oxynitrate is the name applied to a number of compounds that contain Bi3+, nitrate ions and oxide ions and which can be considered as compounds formed from Bi2O3, N2O5 and H2O. Other names for bismuth oxynitrate include bismuth subnitra ...

Structure

The ion is the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...

, consisting of one central

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seven ...

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, g ...

surrounded by three identically bonded

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...

atoms in a

trigonal planar In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands a ...

arrangement. The nitrate ion carries a

formal charge In chemistry, a formal charge (F.C. or q), in the covalent view of chemical bonding, is the charge assigned to an atom in a molecule, assuming that electrons in all chemical bonds are shared equally between atoms, regardless of relative electroneg ...

of −1. This charge results from a combination formal charge in which each of the three oxygens carries a − charge, whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion. This arrangement is commonly used as an example of resonance. Like the

isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in ...

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

ion, the nitrate ion can be represented by resonance structures:

Dietary nitrate

A rich source of inorganic nitrate in the human diets come from leafy green foods, such as

spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...

and

arugula Arugula (American English) or rocket (Commonwealth English) (''Eruca vesicaria''; syns. ''Eruca sativa'' Mill., ''E. vesicaria'' subsp. ''sativa'' (Miller) Thell., ''Brassica eruca'' L.) is an edible annual plant in the family Brassicaceae used a ...

. (inorganic nitrate) is the viable active component within

beetroot The beetroot is the taproot portion of a beet plant, usually known in North America as beets while the vegetable is referred to as beetroot in British English, and also known as the table beet, garden beet, red beet, dinner beet or golden bee ...

juice and other vegetables. Drinking water is also a dietary source. Dietary nitrate supplementation delivers positive results when testing endurance exercise performance. Ingestion of large doses of nitrate either in the form of pure

sodium nitrate Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. ...

or beetroot juice in young healthy individuals rapidly increases plasma nitrate concentration by a factor of 2 to 3, and this elevated nitrate concentration can be maintained for at least 2 weeks. Increased plasma nitrate stimulates the production of

nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its ...

, NO. Nitric oxide is an important physiological signaling molecule that is used in, among other things, regulation of muscle blood flow and mitochondrial respiration.

Cured meats

Nitrite consumption is primarily determined by the amount of processed meats eaten, and the concentration of nitrates in these meats. Although nitrites are the nitrogen compound chiefly used in meat curing, nitrates are used as well. Nitrates lead to the formation of

nitrosamine In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines ...

s. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants

vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...

and the alpha-tocopherol form of

vitamin E Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in v ...

during curing. Anti-hypertensive diets, such as the

DASH diet The DASH diet (Dietary Approaches to Stop Hypertension) is a dietary pattern promoted by the U.S.-based National Heart, Lung, and Blood Institute (part of the National Institutes of Health (NIH), an agency of the United States Department of Hea ...

, typically contain high levels of nitrates, which are first reduced to

nitrite The nitrite ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite als ...

in the saliva, as detected in

saliva testing Saliva testing or Salivaomics is a diagnostic technique that involves laboratory analysis of saliva to identify markers of endocrine, immunologic, inflammatory, infectious, and other types of conditions. Saliva is a useful biological fluid for ...

, prior to forming

Occurrence and production

Nitrate salts are found naturally on earth in arid environments as large deposits, particularly of

nitratine Nitratine or nitratite, also known as cubic niter (UK: nitre), soda niter or Chile saltpeter (UK: Chile saltpetre), is a mineral, the naturally occurring form of sodium nitrate, NaNO3. Chemically it is the sodium analogue of saltpeter. Nitrati ...

, a major source of

. Nitrates are produced by a number of species of

nitrifying bacteria Nitrifying bacteria are chemolithotrophic organisms that include species of genera such as '' Nitrosomonas'', '' Nitrosococcus'', '' Nitrobacter'', '' Nitrospina'', '' Nitrospira'' and '' Nitrococcus''. These bacteria get their energy from the oxid ...

in the natural environment using

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...

as a source of nitrogen and source of free energy. Nitrate compounds for

gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate ( saltpete ...

were historically produced, in the absence of mineral nitrate sources, by means of various

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

processes using urine and dung. Lightning strikes in earth's nitrogen- and oxygen-rich atmosphere produce a mixture of oxides of nitrogen, which form

nitrous A Nitrous Oxide Engine, or Nitrous Oxide System commonly referred to and known as NOS, is an internal combustion engine in which oxygen for burning the fuel comes from the decomposition of nitrous oxide, N2O, rather than air. The system incr ...

ions and nitrate ions, which are washed from the atmosphere by rain or in occult deposition. Nitrates are produced industrially from

Uses

Agriculture

Nitrates are used as

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

s in

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

because of their high solubility and biodegradability. The main nitrate fertilizers are

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable is ...

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

, and

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

salts. Several million kilograms are produced annually for this purpose.

Firearms

Nitrates are used as oxidizing agents, most notably in explosives, where the rapid oxidation of carbon compounds liberates large volumes of gases (see

for an example). Sodium nitrate is used to remove air bubbles from molten glass and some ceramics. Mixtures of the molten salt are used to harden some metals.

Cinema

Nitrate was also used as a

film stock Film stock is an analog medium that is used for recording motion pictures or animation. It is recorded on by a movie camera, developed, edited, and projected onto a screen using a movie projector. It is a strip or sheet of transparent ...

through

nitrocellulose Nitrocellulose (also known as cellulose nitrate, flash paper, flash cotton, guncotton, pyroxylin and flash string, depending on form) is a highly flammable compound formed by nitrating cellulose through exposure to a mixture of nitric acid and ...

. Due to its high combustibility, the studios swapped to acetate safety film in 1950.

Medicine

In the medical field, nitrates are used in the prophylaxis and management of Acute Coronary Syndromes/MI/Heart attacks. These class of drugs are also known as nitrovasodilators.

Detection

Almost all methods for detection of nitrate rely on its conversion to nitrite followed by nitrite-specific tests. The reduction of nitrate to nitrite is effected by copper-cadmium material. The sample is introduced with a flow injection analyzer, and the resulting nitrite-containing effluent is then combined with a reagent for colorimetric or electrochemical detection. The most popular of these assays is the Griess test, whereby nitrite is converted to a deeply colored

azo dye Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C-N= ...

suited for UV-vis spectroscopic analysis. The method exploits the reactivity of

nitrous acid Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reage ...

derived from acidification of nitrite. Nitrous acid selectively reacts with aromatic amines to give diazonium salts, which in turn couple with a second reagent to give the azo dye. The

detection limit The limit of detection (LOD or LoD) is the lowest signal, or the lowest corresponding quantity to be determined (or extracted) from the signal, that can be observed with a sufficient degree of confidence or statistical significance. However, the ...

is 0.02 to 2 μM. Such methods have been highly adapted to biological samples.

Safety

The

acute toxicity Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as ''acute'' toxicity, the adverse effect ...

of nitrate is low. "Substantial disagreement" exists about the long-term risks of nitrate exposure. The two areas of possible concern are that (i) nitrate could be a precursor to

in the lower gut, and nitrite is a precursor to nitrosamines, which are implicated in carcinogenesis, and (ii) nitrate is implicated in

methemoglobinemia Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications ...

, a disorder of hemoglobin in red blood cells.

Methemoglobinemia

Nitrates do not affect infants and pregnant women. Blue baby syndrome is caused by a number of other factors such as gastric upset, such as diarrheal infection, protein intolerance, heavy metal toxicity etc., with nitrates playing a minor role.

Drinking water standards

Through the Safe Drinking Water Act, the United States Environmental Protection Agency has set a maximum contaminant level of 10 mg/L or 10 ppm of nitrate in drinking water. An acceptable daily intake (ADI) for nitrate ions was established in the range of 0–3.7 mg (kg body weight)⁻¹ day⁻¹ by the Joint FAO/WHO Expert Committee on Food Additives (JEFCA).

Aquatic toxicity

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...

systems close to land, nitrate can reach concentrations that are lethal to fish. While nitrate is much less toxic than ammonia, levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species. Nitrate toxicity remains a subject of debate. In most cases of excess nitrate concentrations in aquatic systems, the primary sources are wastewater discharges, as well as

surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the ...

from agricultural or

landscape A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or man-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionary''. A landscape includes the p ...

d areas that have received excess nitrate fertilizer. The resulting

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplank ...

and algae blooms result in anoxia and dead zones. As a consequence, as nitrate forms a component of

total dissolved solids Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular, ionized, or micro-granular ( colloidal sol) suspended form. TDS concentrations are often report ...

, they are widely used as an indicator of water quality.

Domestic animal feed

Symptoms of nitrate poisoning in domestic animals include increased heart rate and respiration; in advanced cases blood and tissue may turn a blue or brown color. Feed can be tested for nitrate; treatment consists of supplementing or substituting existing supplies with lower nitrate material. Safe levels of nitrate for various types of livestock are as follows: The values above are on a dry (moisture-free) basis.

Salts and covalent derivatives

Nitrate formation with elements of the periodic table:

References

External links

ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity
{{Authority control Curing agents Functional groups Garde manger Nitrogen cycle Non-coordinating anions Oxyanions Water quality indicators