Types of column chromatography: On the basis of type of interaction between the stationary and the mobile phases the column chromatography can be divided into following types.
- Adsorption chromatography
- Partition chromatography
- Ion-Exchange chromatography
- Molecular Exclusion (Gel Filtration) chromatography
- Affinity chromatography
Adsorption chromatography
Adsorption is a surface phenomenon in which molecules get attached to column particle. The molecule is called adsorbate while column particle is adsorbent . Molecules can be separated based on their adsorption properties. Many inert materials can be used as adsorbents. e.g. alumina, charcoal, calcium carbonate.
Partition chromatography
Chromatography is a non destructive separation technique for successful separation and purification of individual components of a complex mixture which can not be separated by usual methods due to their similar physical and chemical properties. The basic principal of any chromatography is, how a compound get distributed in between two immiscible phases, a stationary phase and a mobile phase. Those components have higher affinity for the stationary phase are retained longer in the system than those that are distributed selectively in the mobile phase. As a consequence, solutes are eluted from the system as local concentrations in the mobile phase in the order of their increasing distribution coefficients with respect to the stationary phase which leads the separation of different components of mixture.
An analyte remains in equilibrium between the two phases;
Amobile  A stationary
The equilibrium constant, K d is termed the partition coefficient or distribution coefficient , defined as the molar concentration of analyte in the stationary phase divided by the molar concentration of the analyte in the mobile phase. It explains about the distribution of a compound in between two phases. Suppose there are two phases A & B (immiscible to each other) and these are present together. When a compound X is mixed, it distributes itself in these two phases and the concentration of compound in phase A is XA and in phase B is X B . The distribution coefficient of X can be expressed as,
Kd = XA /X B (Kd is a constant at a particular temperature)
|
