Chromatography and Its types

Chromatography is a physical technique of separation, identification and purification of components of a mixture. The term chromatography was derived from Greek word meaning color writing and was first introduced in 1906 by a Russian Botanist Mikhail Tsvet. This technique of chromatography was introduced by Tsvet and later developed by Martin and Synge 1941. Tsvet experiments we’re concerned with the separation of components of dissolved leaf extracts.In this experiment, a leaf extracts sample in petroleum ether was allowed to pass through a column of Calcium carbonate. Pure ether was allowed to flow through the column, as a result of which various chlorophyll pigments were separated into a series of differently colored and easily distinguished zones. Martin and co-workers used silica gel packed column for separation and were awarded Nobel prize in 1952 for this work.

The technique of chromatography involves two phases in contact with each other. One of the phase is called stationary phase which is usually finely divided solid or thin layer of a liquid supported on a finely divided solid. The other phase is called a moving or mobile phase which may be a liquid or a gas.

Chromatography consists of a group of techniques that are used to separate the components of mixture which are very closely related to each other. Chromatography is used in many areas of study particularly in chemistry, biology and medicine. Pigments, dyes, amino acids, vitamins can be separated by using the technique of chromatography.

The technique of chromatography is similar, in some respects, to the technique of solvent extraction. In solvent extraction, a solute is soluble in two immiscible liquids and has definite solubility ratio in them called partition coefficient. In chromatography, a solute is distributed in two phases called stationary phase and mobile phase, in a definite proportion.

Chromatography

Principle of Separation

In chromatography, the mixture to be separated is kept in contact with the stationary phase and mobile phase. The mobile phase which is a flow of liquid or a gas is allowed to move over the stationary phase. The mobile phase acts as a driving force and sets the components in motion. The stationary phase provides a retarding force. The retardation takes place either by the way of adsorption of the components on the solid or partition (distribution) of the components between the two fluids. Different components of the mixture differ in their adsorption- desorption behavior or partitioning behavior and therefore retarded to different extent. In this way, these small differences in adsorption- desorption behavior or partitioning behavior are multiplied several times leading to an easy and clear separation of components of a mixture.

Types of Chromatography

Chromatographic processes are classified mainly into two types;

• 1.       Adsorption chromatography

• 2.       Partition chromatography

In Adsorption chromatography, stationary phase is solid and mobile phase is liquid or gas. In Adsorption chromatography, where mobile phase is liquid are column chromatography, Thin layer chromatography (TLC) and ion-exchange chromatography. And where mobile phase is gas known as gas chromatography.

In partition chromatography, stationary phase is liquid and mobile phase is liquid or gas. In partition chromatography, where mobile phase is liquid are paper chromatography and gel chromatography. And where mobile phase is gas is known as gas liquid chromatography.

 It should be noted that this is very broad classification and does not give a very clear distinction between any two processes. A given process may be sometimes a combination of both, the Adsorption and partition chromatography. Similarly one can not exclude the possibility of partition as a mechanism in column or thin layer chromatography.

 Arranged by Shubhangi