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What is the basic principle of chromatography?

The process of separating compounds from one another by passing the mixture through a column that holds some compounds longer than others is called chromatography.

 

A solution having compounds C and D is placed on top of column formerly filled with solid particles and solvent.

When the outlet is opened, C and D flow down in to the column and are washed through with fresh solvent applied to the top of the column.

If solute C is adsorbed (attach to solid particles surface) more strongly than solute D, then C stays a smaller time free in solution.

Solute C moves down very slowly from the column than D and comes out at the bottom after D. (refer to the figure below).

 

 

The mobile phase (solvent travelling through the column) in chromatography is either a liquid or a gas.

The stationary phase (the substance that remains permanent inside the column) is either a solid or a liquid which are covalently bonded to solid particles or inside the wall of a hollow capillary column.

Partitioning of the solutes between the mobile and stationary phases, give rise to separation. In gas chromatography, mobile phase is gas and in liquid chromatography, mobile phase is liquid.

 

Fluid entering the column is called eluent. Fluid exiting the column is called eluate. The process of passing liquid or gas through a chromatography column is called elution. Refer to the below figure.

 

   

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 Chromatography

  • Used to separate mixtures into their components, purify compounds, and also to test the purity of compounds

  • Two important classes − Adsorption chromatography and partition chromatography

Adsorption Chromatography

  • Based on the fact that different compounds are adsorbed on an adsorbent to different degrees

  • Commonly used adsorbents − Silica gel and alumina

  • A mobile phase is allowed to move over a stationary phase (adsorbent). Then the components of the mixture move by varying distance over the stationary phase.

Partition Chromatography

  • Based on continuous differential partitioning of components of mixture between stationary and mobile phases

  • Paper chromatography is a type of partition chromatography.

  • For paper chromatography, chromatography paper (a special type of paper) is used which contains water trapped in it and acts as the stationary phase.

  • The chromatography paper retains different components according to their differing partition in the two phases.

  • The developed paper is called chromatogram.

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