Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble 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 of nitric acid, consisting of one central nitrogen atom surrounded by three identically bonded oxygen 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 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 beet ...

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. T ...

or beetroot juice in young healthy individuals rapidly increases

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

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 che ...

, 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 are ...

s. The production of carcinogenic nitrosamines may be inhibited by the use of the antioxidants vitamin C and the alpha-tocopherol form of vitamin E during curing. Anti-hypertensive diets, such as the DASH diet, typically contain high levels of nitrates, which are first reduced to

nitrite The nitrite polyatomic ion, 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 ...

in the saliva, as detected in saliva testing, prior to forming

Occurrence and production

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

. Nitrates are produced by a number of species of nitrifying bacteria in the natural environment using ammonia or urea as a source of nitrogen and source of free energy. Nitrate compounds for gunpowder 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 ions and nitrate ions, which are washed from the atmosphere by rain or in occult deposition. Nitrates are produced industrially from nitric acid.

Uses

Agriculture

Nitrates are used as fertilizers in agriculture 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, potassium, calcium, and magnesium 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 gunpowder 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 p ...

through nitrocellulose. 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 A nitrovasodilator is a pharmaceutical agent that causes vasodilation (widening of blood vessels) by donation of nitric oxide (NO), and is mostly used for the treatment and prevention of angina pectoris. This group of drugs includes nitrates (est ...

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=N ...

suited for UV-vis spectroscopic analysis. The method exploits the reactivity of nitrous acid 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 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 Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eig ...

, 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 m ...

, 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 include ...

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 environment ...

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 th ...

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 ...

d areas that have received excess nitrate fertilizer. The resulting eutrophication and algae blooms result in anoxia and dead zones. As a consequence, as nitrate forms a component of total dissolved solids, 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