Elution

Not to be confused withelutriation.

Elution principle of column chromatography

Inanalyticalandorganicchemistry,elutionis the process of extracting one material from another by washing with a solvent: washing of loadedion-exchange resinsto remove capturedions,or elutingproteinsor otherbiopolymersfrom agelelectrophoresisorchromatography column.

In a liquidchromatographyexperiment, for example, ananalyteis generally adsorbed by ( "bound to" ) anadsorbentin a liquid chromatography column. The adsorbent, a solid phase, called a "stationary phase", is a powder which is coated onto a solid support. Based on an adsorbent's composition, it can have varyingaffinitiesto "hold onto" other molecules—forming a thin film on the surface of its particles.Elutionthen is the process of removing analytes from the adsorbent by running a solvent, called an "eluent", past the adsorbent–analyte complex. As the solvent molecules "elute", or travel down through the chromatography column, they can either pass by the adsorbent–analyte complex or displace the analyte by binding to the adsorbent in its place. After the solvent molecules displace the analyte, the analyte can be carried out of the column for analysis. This is why as the mobile phase, called an "eluate", passes out of the column, it typically flows into adetectoror is collected by a fraction collector for compositional analysis.

Predicting and controlling the order of elution is a key aspect of column chromatographic andcolumn electrophoreticmethods.

Eluotropic series

Aneluotropic seriesis listing of various compounds in order of eluting power for a givenadsorbent.The "eluting power" of asolventis largely a measure of how well the solvent can "pull" ananalyteoff the adsorbent to which it is attached. This often happens when the eluent adsorbs onto the stationary phase, displacing the analyte. Such series are useful for determining necessary solvents needed forchromatographyof chemical compounds. Normally such a series progresses from non-polar solvents, such asn-hexane,to polar solvents such asmethanolorwater.The order of solvents in an eluotropic series depends both on thestationary phaseas well as on the compound used to determine the order.

Adsorption strength (least strongly adsorbed → most strongly adsorbed)
Saturated hydrocarbons; alkyl halides	Unsaturated hydrocarbons; alkenyl halides	Aromatic hydrocarbons; aryl halides	Polyhalogenated hydrocarbons	Ethers	Esters	Aldehydes and ketones	Alcohols	Acids and bases (amines)

Eluting power (least eluting power → greatest eluting power)
Hexane or pentane	Cyclohexane	Benzene	Dichloromethane	Chloroform	Ether (anhydrous)	Ethyl acetate (anhydrous)	Acetone (anhydrous)	Methanol	Ethanol	Pyridine	Acetic acid	Water

Eluent

Theeluentoreluantis the "carrier" portion of the mobile phase. It moves the analytes through thechromatograph.Inliquid chromatography,the eluent is the liquid solvent; ingas chromatography,it is the carrier gas.

Eluate

Theeluatecontains theanalytematerial that emerges from thechromatograph.It specifically includes both the analytes and coeluting solutes passing through the column, while the eluent is only the carrier.

Elution time and elution volume

The "elution time "of a solute is the time between the start of the separation (the time at which the solute enters the column) and the time at which the solute elutes. In the same way, theelution volumeis the volume of eluent required to cause elution. Under standard conditions for a known mix of solutes in a certain technique, the elution volume may be enough information to identify solutes. For instance, a mixture ofamino acidsmay be separated byion-exchange chromatography.Under a particular set of conditions, the amino acids will elute in the same order and at the same elution volume.

Antibody elution

Antibody elutionis the process of removing antibodies that are attached to their targets, such as the surface ofred blood cells.Techniques include using heat, a freeze-thaw cycle, ultrasound, acids or organic solvents. No single method is best in all situations.

See also

• Chromatography
• Desorption
• Electroelution
• Gradient elutionin high performance liquid chromatography
• Leaching

References

• Brown, Phillis (2001).Advances in chromatography.CRC Press.p. 36.ISBN0-8247-0509-2.

External links

• Chemistry glossary
• Eluotropic seriesArchived2015-12-22 at theWayback Machine