chromatography

The separation of chemical substances and particles (originally plant pigments and other highly colored compounds) by differential movement through a two-phase system. The mixture of materials to be separated is percolated through a column or sheet of some suitable chosen absorbent ( e.g., an ion-exchange material); the substances least absorbed are least retarded and emerge the earliest; those more strongly absorbed emerge later. SYN: absorption c.. [chromato- + G. grapho, to write]

- absorption c. SYN: c..

- adsorption c. c. in which separation of substances is achieved by the difference in degree of adsorption of the compounds to a stationary phase.

- affinity c. c. where the absorbent has a unique chemical affinity for a particular component of the passing solution. SYN: affinity column.

- column c. a form of partition, adsorption, ion exchange, or affinity c. in which one phase is liquid (aqueous) flowing down a column packed with the second phase, a solid; the dissolved substances form a partition between the solid and liquid phases depending on the chemical and physical conditions of each phase; the more strongly adsorbed solutes reach the bottom of the column later than the less strongly adsorbed ones.

- gas c. a chromatographic procedure in which the mobile phase is a mixture of gases or vapors, which are separated in the process by their differential adsorption on a stationary phase.

- gas-liquid c. (GLC) gas c., with the stationary phase being liquid rather than solid.

- gel filtration c. gel filtration.

- high-performance liquid c. (HPLC) a chromatographic technology used to separate and quantitate mixtures of substances in solution. A sample is injected into a moving stream of solvent that flows through a column and detector. Separation during passage through the column occurs by absorption, partition, ion exchange, or size exclusion. The technique is commonly used in laboratories to measure organic compounds including steroid hormones, pesticides and poisons, toxic and carcinogenic compounds, and drugs. SYN: high-pressure liquid c..

- high-pressure liquid c. (HPLC) SYN: high-performance liquid c..

- ion exchange c. c. in which cations or anions in the mobile phase are separated by electrostatic interactions with the stationary phase. SEE ALSO: anion exchange, cation exchange.

- liquid-liquid c. c. in which both the moving phase and the stationary (or reverse-moving) phase are liquids, as in countercurrent distribution.

- paper c. partition c. in which the moving phase is a liquid and the stationary phase is paper.

- partition c. the separation of similar substances by repeated divisions between two immiscible liquids, so that the substances, in effect, cross the partition between the liquids in opposite directions; where one of the liquids is bound as a film on filter paper, the process is termed paper partition c. or paper c..

- reversed phase c. a form of partitionary c. in which the stationary phase is less polar than the mobile phase.

- thin-layer c. (TLC) c. through a thin layer of cellulose or similar inert material supported on a glass or plastic plate.

- two-dimensional c. paper c. in which a spot, located originally in one corner of a sheet, is developed in one direction along one side of the sheet, after which the sheet is rotated 90° and developed, with another solvent, in the new direction; the resultant spots are thus spread over the entire paper, giving a “map” or “fingerprint.” Also generalized to include c. followed by electrophoresis (or vice versa), column c. followed by paper c., etc.

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chro·ma·tog·ra·phy .krō-mə-'täg-rə-fē n, pl -phies a process in which a chemical mixture carried by a liquid or gas is separated into components as a result of differential distribution of the solutes as they flow around or over a stationary liquid or solid phase see AFFINITY CHROMATOGRAPHY, COCHROMATOGRAPHY, COLUMN CHROMATOGRAPHY, ELECTROCHROMATOGRAPHY, GAS CHROMATOGRAPHY, GAS-LIQUID CHROMATOGRAPHY, GEL FILTRATION, HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY, ION-EXCHANGE CHROMATOGRAPHY, LIQUID CHROMATOGRAPHY, PAPER CHROMATOGRAPHY, PARTITION CHROMATOGRAPHY, RADIOCHROMATOGRAPHY, THIN-LAYER CHROMATOGRAPHY

chro·mato·graph·ic krō-.mat-ə-'graf-ik, krə- adj

chro·mato·graph·i·cal·ly -i-k(ə-)lē adv

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n.

any of several techniques for separating the components of a mixture by selective absorption. Two such techniques are quite widely used in medicine, for example to separate mixtures of amino acids. In one of these, paper chromatography, a sample of the mixture is placed at the edge of a sheet of filter paper. As the solvent soaks along the paper, the components are absorbed to different extents and thus move along the paper at different rates. In column chromatography the components separate out along a column of a powdered absorbent, such as silica or aluminium oxide.

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chro·ma·tog·ra·phy (kro″mə-togґrə-fe) any of a diverse group of techniques used to separate mixtures of substances based on differences in the relative affinities of the substances for two different media, one (the mobile phase) a moving fluid and the other (the stationary phase or sorbent) a porous solid or gel or a liquid coated on a solid support; the speed at which each substance is carried along by the mobile phase depends on its solubility (in a liquid mobile phase) or vapor pressure (in a gas mobile phase) and on its affinity for the sorbent. chromatographic adj