Chromatography (paper chromatography,Greek Chroma, color; Graphe, writing) is technique for the separation of mixture of solutes brought about by the dynamic partition or, distribution of dissolved or dispersed materials between Two immiscible phases, one of which goes beyond the other. As the name suggests, this technique Was originally confined to the separation of colored substances, such as plant pigments or dyestuff. Now the technique is equally well applied to colorless substances.
Definitions of Chromatography
Chromatography can be defined in various ways. Some common definitions of chromatography are: .
- Chro-matography is any process which is run in a column using a fixed bed.
- Chromatography is the name given to the technique for the separation of a mixture. The solutes brought about by the dynamic partition or distribution of dissolved materials between two immiscible phases one of which is moving past the other.
- Strain has defined chro-matography as any analytical technique for resolution of solutes, in which separation is made by differential migration in a porous medium and the migration is caused by flow of solvent.
- According to Williams and Weil the chromatography is a process which allows the resolution of mixtures by effecting separation of some or all of their components in concentration zones on or in phases different from those in which they are_originally present, irrespective of the nature of force or forces causing the substance to move from one phase to another.
Types of Paper chromatography:
Paper chromatography can be divided into two classes:
(a) Paper Partition chro-matography.
In this technique chromatographic filter paper acts as an inert support in which one solvent (usually water present in the Cellulose of the filter paper) acts as a stationary phase. The other solvent (usually an organic solvent) acts as a mobile phase. Thus, the substances in e mixture move in two non-mixing solvents and partition between them.
(b)) Adsorption paper chro-matography.
In adsorption paper chromatography the filter paper is impregnated with an adsorbent such as alumina or silica. A single solvent is allowed to flow over the unknown components. Thus, some of the components may be adsorbed more strongly than the others causing in the variation in the amount of the substance which tends to flow with the solvent. This causes the separation of the components.