<Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (July 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (July 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> 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 . </P> <Ul> <Li> 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 . this is true . </Li> <Li> 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 . </Li> <Li> 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 . </Li> <Li> Evaporation removes volatile liquids from non-volatile solutes, which cannot be done through filtration due to the small size of the substances . </Li> <Li> 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 . </Li> <Li> 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 . </Li> <Li> 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 . </Li> <Li> 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 adsorption and desorption on a packed bed of a solid to purify multiple components of a single feed stream . </Li> <Li> Smelting produces metals from raw ore, and involves adding chemicals to the ore and heating it up to the melting point of the metal . </Li> <Li> 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 . </Li> <Li> Distillation, widely used in petroleum refining and in purification of ethanol separates volatile liquids on the basis of their relative volatilities . </Li> </Ul>

The seperation technique that improves on the purity of a compound is