can sombody explain about chromatography?

Question

what conditions are neccesary for substances to be separated by chromatography?
why might different solvents be used in chromatography?

Answer 1

Chromatography (literally= color writing) involves a stationary phase and a mobile phase. The stationary phase might be paper, silica gel (thin layer and column chromatograpy), or various chemicals used in gas chromatography such as silica oil or carbowax. The mobile phase (a solution in paper or thin layer chromatography) moves along the stationary phase by capillary action, or by gas flowing through it. The relative attractions between the substance being tested and either the mobile or stationary phases is the basis for separation. If the substance has more "attraction" for the mobile phase it will move farther and quicker alone the stationary phase. If the substance tested has a greater affinty for the mobile phase, it will move a shorter distance in the same amount of time. Often special treatment is necessary to visualize a thin-layer or paper chromatogram. Sometimes they are simple sprayed with chemicals that will make the substance visible. Other methods of visualizing involve the use of ultraviolet light or heat. A gas chromatograph has a detector that changes the resistance in a circuit when substances different from the carrier gas (mobile) passes over in containing the substances.

Answer 2

Chromatography (from Greek chroma, colour) is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated.

Chromatography terms

* The analyte is the substance which is to be purified or isolated during chromatography
* Analytical chromatography is used to determine the identity and concentration of molecules in a mixture
* A chromatogram is the visual output of the chromatograph. Different peaks or patterns on the chromatogram correspond to different components of the separated mixture
* A chromatograph takes a chemical mixture carried by liquid or gas and separates it into its component parts as a result of differential distributions of the solutes as they flow around or over the stationary phase
* The mobile phase is the analyte and solvent mixture which travels through the stationary phase
* Preparative chromatography is used to nondestructively purify sufficient quantities of a substance for further use, rather than analysis.
* The retention time is the characteristic time it takes for a particular molecule to pass through the system under set conditions.
* The stationary phase is the substance which is fixed in place for the chromatography procedure and is the phase to which solvents and the analyte travels through or binds to. Examples include the silica layer in thin layer chromatography.

Answer 3

Chromatography, in chemistry, analytical technique is used for the chemical separation of mixtures and substances. The technique depends on the principle of selective adsorption (not to be confused with absorption), a type of adhesion.
For example, in paper chromatography, various components of a mixture gets adsorbed in different levels of the paper.
The more easily ,the component get adsorbed, the lower the level of the absorption area of the paper.

Answer 4

For substances to be separated by Chromatography they have to have different polarity in the selected solventt. On this basis, solvents of different polarities could be used to separate different substances. The migration of a substance in a given solven is a function of its polarity in that solvent.

Answer 5

There are many different conditions. what you are trying to seperates have similar properties or different properties will lead you to choose the technique. For small compounds (small molecular mass) you may use GC or similar one. seperation process depends on polarity, acidity or other characteristics of molecules. retention time (time for molecules travelling through Column) differs and finally you get molecules one by one at the end point of column (at the detector)
for seperation process you can use GC, HPLC, TLC or IC depending on molecules

Ayhan