List of purification methods in chemistry
Purification in a chemical context is the physical separation of a chemical substance of interest from foreign or contaminating substances. The following list of chemical purification methods should not be considered exhaustive.
- Affinity purification is used to purify proteins by retaining them on a column through their affinity to antibodies, enzymes or receptors which 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 in which light particles are revolved over high speed with the help of electric motor so that the fine particles which do not settle at bottom would settle down.
- Evaporation is used to remove volatile liquids from non-volatile solutes which cannot be done through filtration due to the small size of the substances.
- Solvent extraction removes an impurity, or recovers a desired product, by dissolving it in a solvent in which other components of the feed material are soluble.
- Crystallization separates a product from a liquid feedstream, often in extremely pure form, by cooling the feedstream or adding precipitants which 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 recrystallized, e.g. dissolved in a very pure solvent, and then crystallized, and the crystals recovered, in order to improve and/or verify their purity.
- Adsorption removes a soluble impurity from a feedstream by trapping it on the surface of a solid material such as activated carbon which forms strong noncovalent chemical bonds with the impurity. Chromatography employs adsorption and desorption on a packed bed of a solid to purify multiple components of a single feedstream.
- Smelting is used to produce 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.
- 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.
- Bioleaching is the extraction of metals from their ores through the use of living organisms.
USING A SEPARATING FUNNEL
Immiscible liquids,such as oil and water can be separated by using a separating funnel. The mixture is put into a separating funnel, shaken and allowed to settle. The oil and water from two separate layer. The liquid with higher density, in this case water forms the lower layer. Remove the stopper and open the tap after standing. The water runs out through the tap. The oil remains in the funnel and can be run out into another beaker.
A useful technique for dissolving out a component from a mixture using a suitable solvent is called SOLVENT EXTRACTION.
Assume we wish to extract iodine which is dissolved in water together with some impurities. Iodine is more soluble than water. We can put the aqueous solution of iodine into a separating funnel and add 1,1,1-trichloroethane to it. Water and 1,1,1-trichloroethane form two separate layers because they are immiscible. After shaking, most of the iodine will then dissolve in the 1,1,1-trichloroethane layer. 1,1,1-trichloroethane from water, pure iodine can then be obtained by evaporating after separating.