Citric acid in the context of Chelating agent

Carl Wilhelm Scheele (German: [ˈʃeːlə], Swedish: [ˈɧêːlɛ]; 9 December 1742 – 21 May 1786) was a German-Swedish pharmaceutical chemist.

Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified the elements molybdenum, tungsten, barium, nitrogen, and chlorine, among others. Scheele discovered organic acids tartaric, oxalic, uric, lactic, and citric, as well as hydrofluoric, hydrocyanic, and arsenic acids. He preferred speaking German to Swedish his whole life, as German was commonly spoken among Swedish pharmacists.

Purification in a chemical context is the physical separation of a chemical substance of interest from foreign or contaminating substances. Pure results of a successful purification process are termed isolate. The following list of chemical purification methods should not be considered exhaustive.

• Affinity purification purifies proteins by retaining them on a column through their affinity to antibodies, enzymes, or receptors that have been immobilised on the column.
• Filtration is a mechanical method to separate solids from liquids or gases by passing the feed stream through a porous sheet such as a cloth or membrane, which retains the solids and allows the liquid to pass through.
• Centrifugation is a process that uses an electric motor to spin a vessel of fluid at high speed to make heavier components settle to the bottom of the vessel.
• Evaporation removes volatile liquids from non-volatile solutes, which cannot be done through filtration due to the small size of the substances.
• Liquid–liquid extraction removes an impurity or recovers a desired product by dissolving the crude material in a solvent in which other components of the feed material are soluble.
• Crystallization separates a product from a liquid feed stream, often in extremely pure form, by cooling the feed stream or adding precipitants that lower the solubility of the desired product so that it forms crystals. The pure solid crystals are then separated from the remaining liquor by filtration or centrifugation.
• Recrystallization: In analytical and synthetic chemistry work, purchased reagents of doubtful purity may be recrystallised, e.g. dissolved in a very pure solvent, and then crystallized, and the crystals recovered, in order to improve and/or verify their purity.
• Trituration removes highly soluble impurities from usually solid insoluble material by rinsing it with an appropriate solvent.
• Adsorption removes a soluble impurity from a feed stream by trapping it on the surface of a solid material, such as activated carbon, that forms strong non-covalent chemical bonds with the impurity.
• Chromatography employs continuous adsorption and desorption on a packed bed of a solid to purify multiple components of a single feed stream. In a laboratory setting, mixture of dissolved materials are typically fed using a solvent into a column packed with an appropriate adsorbent, and due to different affinities for solvent (moving phase) versus adsorbent (stationary phase) the components in the original mixture pass through the column in the moving phase at different rates, which thus allows to selectively collect desired materials out of the initial mixture.
• Smelting produces metals from raw ore, and involves adding chemicals to the ore and heating it up to the melting point of the metal.
• Refining is used primarily in the petroleum industry, whereby crude oil is heated and separated into stages according to the condensation points of the various elements.
• Distillation, widely used in petroleum refining and in purification of ethanol separates volatile liquids on the basis of their relative volatilities. There are several type of distillation: simple distillation, steam distillation etc.
• Water purification combines a number of methods to produce potable or drinking water.
• Downstream processing refers to purification of chemicals, pharmaceuticals and food ingredients produced by fermentation or synthesized by plant and animal tissues, for example antibiotics, citric acid, vitamin E, and insulin.
• Fractionation refers to a purification strategy in which some relatively inefficient purification method is repeatedly applied to isolate the desired substance in progressively greater purity.
• Electrolysis refers to the breakdown of substances using an electric current. This removes impurities in a substance that an electric current is run through
• Sublimation is the process of changing of any substance (usually on heating) from a solid to a gas (or from gas to a solid) without passing through liquid phase. In terms of purification - material is heated, often under vacuum, and the vapors of the material are then condensed back to a solid on a cooler surface. The process thus in its essence is similar to distillation, however the material which is condensed on the cooler surface then has to be removed mechanically, thus requiring different laboratory equipment.
• Bioleaching is the extraction of metals from their ores through the use of living organisms.

Separation process

Vinaigrette (/ˌvɪnɪˈɡrɛt/ VIN-ig-RET, French: [vinɛɡʁɛt] ) is a dressing made by mixing an edible oil with a mild acid such as vinegar (acetic acid) or lemon juice (citric acid). The mixture can be enhanced with salt, herbs and/or spices. It is used most commonly as a salad dressing, but can also be used as a marinade.

Traditionally, a vinaigrette consists of 3 parts oil and 1 part vinegar mixed into a stable emulsion, but the term is also applied to mixtures with different proportions and to unstable emulsions which last only a short time before separating into layered oil and vinegar phases.

The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle)—is a series of biochemical reactions that release the energy stored in nutrients through acetyl-CoA oxidation. The energy released is available in the form of ATP. The Krebs cycle is used by organisms that generate energy via respiration, either anaerobically or aerobically (organisms that ferment use different pathways). In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, which are used in other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest metabolism components. Even though it is branded as a "cycle", it is not necessary for metabolites to follow a specific route; at least three alternative pathways of the citric acid cycle are recognized.

Its name is derived from the citric acid (a tricarboxylic acid, often called citrate, as the ionized form predominates at biological pH) that is consumed and then regenerated by this sequence of reactions. The cycle consumes acetate (in the form of acetyl-CoA) and water and reduces NAD to NADH, releasing carbon dioxide. The NADH generated by the citric acid cycle is fed into the oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of ATP.

Industrial fermentation is the intentional use of fermentation in manufacturing processes. In addition to the mass production of fermented foods and drinks, industrial fermentation has widespread applications in chemical industry. Commodity chemicals, such as acetic acid, citric acid, and ethanol are made by fermentation. Moreover, nearly all commercially produced industrial enzymes, such as lipase, invertase and rennet, are made by fermentation with genetically modified microbes. In some cases, production of biomass itself is the objective, as is the case for single-cell proteins, baker's yeast, and starter cultures for lactic acid bacteria used in cheesemaking.

In general, fermentations can be divided into four types:

The lemon (Citrus × limon) is a species of small evergreen tree in the Citrus genus of the flowering plant family Rutaceae. A true lemon is a hybrid of the citron and the bitter orange. Its origins are uncertain, but some evidence suggests lemons originated during the 1st millennium BC in what is now northeastern India. Some other citrus fruits are called lemon.

The yellow fruit of the lemon tree is used throughout the world, primarily for its juice. The pulp and rind are used in cooking and baking. The juice of the lemon is about 5–6% citric acid, giving it a sour taste. This makes it a key ingredient in drinks and foods such as lemonade and lemon meringue pie.

A clementine (Citrus × clementina) is a tangor, a citrus fruit hybrid between a willowleaf mandarin orange (C. × deliciosa) and a sweet orange (C. × sinensis), named in honor of Clément Rodier, a French missionary who first discovered and propagated the cultivar in Algeria. The exterior is a deep orange colour with a smooth, glossy appearance. Clementines can be separated into 7 to 14 segments. Similar to tangerines, they tend to be easy to peel. They are typically juicy and sweet, with less acid than oranges. Their oils, like other citrus fruits, contain mostly limonene as well as myrcene, linalool, α-pinene and many complex aromatics.

They are sometimes sold under the name Easy-peelers.

Aspergillus niger is a mold classified within the Nigri section of the Aspergillus genus. The Aspergillus genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on decomposing matter, and suspended in the air. Species within this genus often grow quickly and can sporulate within a few days of germination. A combination of characteristics unique to A. niger makes the microbe invaluable to the production of many acids, proteins and bioactive compounds. Characteristics including extensive metabolic diversity, high production yield, secretion capability, and the ability to conduct post-translational modifications are responsible for A. niger's robust production of secondary metabolites. A. niger's capability to withstand extremely acidic conditions makes it especially important for the industrial production of citric acid.

A. niger causes a disease known as "black mold" on certain fruits and vegetables such as grapes, apricots, onions, and peanuts, and is a common contaminant of food. It is ubiquitous in soil and is commonly found in indoor environments, where its black colonies can be confused with those of Stachybotrys (species of which have also been called "black mold"). A. niger is classified as generally recognized as safe (GRAS) by the US Food and Drug Administration for use in food production, although the microbe is capable of producing toxins that affect human health.

A lime is the fruit of several species of citrus, most of which are hybrids within the genus Citrus (family Rutaceae). Limes are generally small, round to oval fruits with green flesh and skin and a distinctly sour taste due to their high citric acid content. They are widely cultivated in tropical and subtropical regions for culinary, medicinal, and ornamental purposes.

The term "lime" is used for a variety of citrus fruits, including the Key lime (Citrus × aurantiifolia), Persian lime (Citrus × latifolia), Makrut lime (Citrus hystrix), finger lime (Citrus australasica), blood lime (hybrid), and desert lime among others. Limes are a rich source of vitamin C and are used to accent the flavours of foods and beverages. In 2023, world production of limes (combined with lemons) was 23.6 million tonnes, led by India and Mexico.

Sourness, also known as sour, is a basic taste sensation perceived through hydrogen ions from acidic compounds interacting with taste bud receptors, and it can also refer to an unpleasant or acidic quality in taste, disposition, or tone. It is a warning sign for potentially spoiled food, though it is balanced in some food products by sweetness, and it is associated with a low pH.

The most common foods with natural sourness are fruits, such as lemon, lime, grape, orange, tamarind, and bitter melon. Fermented foods, such as wine, sour cream, vinegar or yogurt, may have sour taste. Children show a greater enjoyment of sour flavors than adults, and sour candy containing citric acid or malic acid is common.

Ceviche, cebiche, sebiche, or seviche (Spanish pronunciation: [seˈβitʃe]) is a cold dish consisting of fish or shellfish marinated in citrus and seasonings. Different versions of ceviche are part of the culinary cultures of various Latin American countries along the Pacific Ocean where each one is native, including Chile, Colombia, Costa Rica, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Puerto Rico, Nicaragua, Panama, and Peru. Ceviche is considered the national dish of Peru and is recognized by UNESCO as an expression of Peruvian traditional cuisine and an Intangible Cultural Heritage of Humanity.

The fish or shellfish in ceviche is not served raw like sashimi; the citric acid from the citrus marinade causes the proteins in the seafood to become denatured, resulting in the dish appearing to be "cooked" without the application of heat. The fish is typically cured in lemon or sour lime juice, although sour orange was historically used. The dressing also includes some local variety of chili pepper or chili, replaced by mustard in some parts of Central America. The marinade usually also includes sliced or chopped onions and chopped cilantro, though in some regions such as Mexico, tomatoes, avocadoes, and tomato sauce may be included.

Alpha hydroxy carboxylic acids, or α-hydroxy carboxylic acids (AHAs), are a group of carboxylic acids featuring a hydroxy group located one carbon atom away from the acid group. This structural aspect distinguishes them from beta hydroxy acids, where the functional groups are separated by two carbon atoms. Notable AHAs include glycolic acid, lactic acid, mandelic acid, and citric acid.

α-Hydroxy acids are stronger acids compared to their non-alpha hydroxy counterparts, a property enhanced by internal hydrogen bonding. AHAs serve a dual purpose: industrially, they are utilized as additives in animal feed and as precursors for polymer synthesis. In cosmetics, they are commonly used for their ability to chemically exfoliate the skin.

Sour Patch Kids (also known as Carambar Very Bad Kids in France, and previously known as Maynards Sour Patch Kids in Canada and the UK) are a brand of soft gummy candy with a coating of invert sugar and sour sugar (a combination of citric acid, tartaric acid, and sugar). The tartaric and citric acids provide the candy with a sharp burst of tartness, while the inverted sugar gives the soft gummy its sweet flavor. Sour Patch Kids Extreme, which contains malic acid in addition to the tartaric and citric acids, is considered the sourest variation in the Sour Patch line of candies. The slogans "Sour Then Sweet" and "Sour. Sweet. Gone." refer to the candy's sour-to-sweet taste.

Ammonium ferric citrate (also known as ferric ammonium citrate or ammoniacal ferrous citrate) has the formula [NH₄]{y}[Fe{x}(C₆H₄O₇)]. The iron in this compound is trivalent. All three carboxyl groups and the central hydroxyl group of citric acid are deprotonated. A distinguishing feature of this compound is that it is very soluble in water, in contrast to ferric citrate which is not very soluble.

In its crystal structure each moiety of citric acid has lost four protons. The deprotonated hydroxyl group and two of the carboxylate groups ligate to the ferric center, while the third carboxylate group coordinates with the ammonium.