Elution
Encyclopedia
Elution is a term used in analytical
and organic
chemistry to describe the process of extracting one material from another by washing with a solvent (as in washing of loaded ion-exchange resins to remove captured ions).
In a liquid chromatography
experiment, for example, an analyte
is generally adsorbed, or "bound to", an adsorbent in a liquid chromatography column. The adsorbent, a solid phase (stationary phase), is a powder which is coated onto a solid support. Based on an adsorbent's composition, it can have varying affinities
to "hold" onto other molecules—forming a thin film on its outside surface (or on its internal surface if there are cavities within the compound). Elution then 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 they can 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 passes out of the column, it typically flows into a detector or is collected for compositional analysis.
Predicting and controlling the order of elution is a key aspect of column chromatographic methods.
is largely a measure of how well the solvent can "pull" an analyte
off the adsorbent to which it is attached. This often happens as the eluent adsorbs onto the stationary phase, displacing the analyte. Such series are useful for determining necessary solvents needed for chromatography
of chemical compounds. Normally such a series progresses from non-polar solvents, such as n-hexane, to polar solvents such as methanol
or water
. The order of solvents in an eluotropic series depends both on the stationary phase as well as on the compound used to determine the order.
. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas.
material that emerge from the chromatograph
. It specifically includes both the analytes and solutes passing through the column, while the eluent is only the carrier.
s may be separated by ion-exchange chromatography. Under a particular set of conditions, the amino acids will elute in the same order and at the same elution volume.
Analytical chemistry
Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials. Qualitative analysis gives an indication of the identity of the chemical species in the sample and quantitative analysis determines the amount of...
and organic
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
chemistry to describe the process of extracting one material from another by washing with a solvent (as in washing of loaded ion-exchange resins to remove captured ions).
In a liquid chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
experiment, for example, an analyte
Analyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
is generally adsorbed, or "bound to", an adsorbent in a liquid chromatography column. The adsorbent, a solid phase (stationary phase), is a powder which is coated onto a solid support. Based on an adsorbent's composition, it can have varying affinities
Affinity
Affinity is a word used in a variety of fields, usually to indicate some kind of preference, relationship, or a potential or actual closeness between two entities.Articles dealing with various usages of the word: affinity include:-Commerce and law:...
to "hold" onto other molecules—forming a thin film on its outside surface (or on its internal surface if there are cavities within the compound). Elution then 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 they can 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 passes out of the column, it typically flows into a detector or is collected for compositional analysis.
Predicting and controlling the order of elution is a key aspect of column chromatographic methods.
Eluotropic Series
An eluotropic series is a listing of various compounds in order of eluting power for a given adsorbent. The “eluting power” of a solventSolvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
is largely a measure of how well the solvent can "pull" an analyte
Analyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
off the adsorbent to which it is attached. This often happens as the eluent adsorbs onto the stationary phase, displacing the analyte. Such series are useful for determining necessary solvents needed for chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
of chemical compounds. Normally such a series progresses from non-polar solvents, such as n-hexane, to polar solvents such as methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
or water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. The order of solvents in an eluotropic series depends both on the stationary phase as 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) | Ethanol | Methanol | Water | Pyridine | Acetic Acid |
Eluent
The eluent is the "carrier" portion of the mobile phase. It moves the analytes through the chromatographChromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas.
Eluate
The eluate, or mobile phase is a combination of the mobile phase "carrier" and the analyteAnalyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
material that emerge from the chromatograph
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
. It specifically includes both the analytes and 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, the elution volume is 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 of amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s may be separated by ion-exchange chromatography. Under a particular set of conditions, the amino acids will elute in the same order and at the same elution volume.
External links
See also
- DesorptionDesorptionDesorption is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption . This occurs in a system being in the state of sorption equilibrium between bulk phase and an adsorbing surface...
- Gradient elution in high performance liquid chromatography
- LeachingLeachingIn general, leaching is the extraction of certain materials from a carrier into a liquid . Specifically, it may refer to:...