Normal phase chromatography is one where in the stationary phase is polar in nature and the mobile phase is non-polar in nature.
Chromatography is a separation process which employs two phases i.e. stationary phase and a mobile phase.
The stationary phase is water soluble and polar in nature. While the mobile phase is water insoluble and less polar in nature.
In the initial phases of discovery and development of chromatography, silica was widely used as the stationary phase.
This silica gel is polar in nature and hence this type of chromatography is normal type. While the other ones which do not employ silica gel or any polar stationary phase are considered as reverse phase type.
The mobile phase used in this type are some organic solvents which are non polar.
But interestingly this method of chromatography finds less use in research and industry.
Instead the reverse phase chromatography is widely used. This is because of the wide advantages that method offers.
Normal Phase Chromatography principle
In routine chromatography, sand or silica gel which is polar in nature is used as stationary phase. The mobile phase used is mostly non polar and organic in nature.
When compounds like plant extracts are to be separated, those with polar nature tend to bind to the stationary phase. While the compounds with non-polar nature tend move fast with the non-polar mobile phase as they have less affinity to silica phase Hence the non-polar compounds are eluted out first leaving the polar ones inside. These compounds retained can be seen as colored bands called as chromatograms.
In this method, solvents like water, alcohol and other highly polar ones are avoided from being used as mobile phases. Instead, non-polar solvents like petroleum ether, hexane etc are widely used.
Applications of normal phase chromatography
Tough this method is less widely used, it is still the preferred method for
1. This is the most preferred method for column chromatography.
2. It is used for separation of non-polar compounds in organic chemistry.
3. It is also used to separate plant extracts as the plant material has lot of pigments, lipids etc. which are non-polar in nature.
4. When the components of the mixture are damaged by water, they can be separated by this method.
5. Also isomers and compound which are too hydrophyllic and very hydrophobic can be separated well.
Disadvantages of this method
- Less range of compounds can be tested by this method. Since most of the compounds we use like medicine, food, house hold chemical are polar in nature. They cannot not be analysed by this method. Instead reverse phase chromatography is preferred.
- Precise control of variables like solvent composition, pH is not easy in this method.