Chromatography:
The word “Chromatography” comes from the Greek chromatos (color) and graphein (to write). Chromatography was invented by the Russian botanist Mikhail Tswett. It is the technique to separate chemicals and identifying them by color. It is a technique to separate substances from mixtures. Substance mixture is dissolved in mobiles phase (which may be liquid or gas or fluid). This mobile phase forced to travel through Stationary phase (which is inside column). So, mixture of various molecules enters into column, and different molecules travel through column at different speeds. The molecules which have tighter interaction with stationary phase (in Column), will move slowly compared to other molecule which has less interaction with stationary phase. As a result different molecules can be separated from each other out of column. This process is called elution. This molecule interaction process is called Adsorption.
The word “Chromatography” comes from the Greek chromatos (color) and graphein (to write). Chromatography was invented by the Russian botanist Mikhail Tswett. It is the technique to separate chemicals and identifying them by color. It is a technique to separate substances from mixtures. Substance mixture is dissolved in mobiles phase (which may be liquid or gas or fluid). This mobile phase forced to travel through Stationary phase (which is inside column). So, mixture of various molecules enters into column, and different molecules travel through column at different speeds. The molecules which have tighter interaction with stationary phase (in Column), will move slowly compared to other molecule which has less interaction with stationary phase. As a result different molecules can be separated from each other out of column. This process is called elution. This molecule interaction process is called Adsorption.
Absorption: It means some molecule or atom or ions enter into solid or liquid or gas objects, and get diffused. For example, water gets absorbed in sponge.
Adsorption: In this molecule accumulate on the surface of a material instead of diffusing into material. It is same like liquid on a metal bench.
Paper Chromatography:
Paper chromatography is the basic technique to separate
mixture of colors or pigments. By this
technique we can identify substances. This is easy and requires less
material. For Paper chromatography; solvent, sample, good quality filter paper
and transparent bicker are required. The sample for which we want to separate
colors is placed on a filter paper. Filter paper is placed in a bicker in such a way that sample drop remains nearer to solvent. Solvent in the bicker should be filled in such a way that, it should
not touch directly to chemical drop that was placed on a filter paper. See
below image 1.
This solvent diffuses in paper and as per capillary action
it moves towards upside. It moves up by dissolving sample drop also. Sample
molecules movement to upside depends on polarity. Due to different polarity solubility is
different. If more than one molecules are there in sample, then all are moved at
different speeds. For example: very non
polar chemical will not dissolve in very polar solvent. So it will move fast to
up side. This non similarity will separate molecules from each other. See Image
2.
From this Retention factor (Rf) is calculated. It is the
ratio of the distance traveled by the substance to the distance traveled by the
solvent. Suppose distance traveled by substance is 1.5 cm and distance traveled by solvent is 3.0 cm then, Rf = (Distance traveled by substance) /
(Distance traveled by solvent), so Rf = (1.5 cm / 3.0 cm), hence Rf = 0.5
Thin Layer chromatography (TLC):
Another chromatography technique is Thin Layer chromatography (TLC), which is very similar to Paper chromatography.
In TLC, stationary phase (or solid phase) is coated on TLC plate. Same as paper chromatography bicker is filled with solvent or mixture of solvent.
Now let’s assume that we want to separate X and Y component. Sample is prepared using X and Y component and resultant sample is spotted on a TLC plate near bottom. TLC plate is dipped in a solvent bicker. Due to capillary action this solvent flows up the plate. This solvent will also pass through sample spot.
From sample spot, suppose X component will sit more time on TLC Plate and Y component will sit less time, so Y component will move up fast with solvent to upper direction on TLC Plate. Due to tighter interaction of X component with solvent, it will spent more time to sit on Plate and Y component will move with solvent due to weaker interaction with solvent, so X and Y is separated. It means stronger the interaction (adsorption), molecule will stay near origin and weaker the interaction, molecule will move up fast with solvent.
TLC has advantage over Paper chromatography is to wide range choice of TLC Plate for different adsorbents, and hence provide better separation. Different techniques used for chromatography for different types of analysis.
In TLC, stationary phase (or solid phase) is coated on TLC plate. Same as paper chromatography bicker is filled with solvent or mixture of solvent.
Now let’s assume that we want to separate X and Y component. Sample is prepared using X and Y component and resultant sample is spotted on a TLC plate near bottom. TLC plate is dipped in a solvent bicker. Due to capillary action this solvent flows up the plate. This solvent will also pass through sample spot.
From sample spot, suppose X component will sit more time on TLC Plate and Y component will sit less time, so Y component will move up fast with solvent to upper direction on TLC Plate. Due to tighter interaction of X component with solvent, it will spent more time to sit on Plate and Y component will move with solvent due to weaker interaction with solvent, so X and Y is separated. It means stronger the interaction (adsorption), molecule will stay near origin and weaker the interaction, molecule will move up fast with solvent.
TLC has advantage over Paper chromatography is to wide range choice of TLC Plate for different adsorbents, and hence provide better separation. Different techniques used for chromatography for different types of analysis.
There
are different chromatography techniques available, such as Paper chromatography,
Thin Layer chromatography, Liquid Chromatography, Gas chromatography, Ion
Exchange chromatography, Size Exclusion chromatography and many more.
Important Note: Procedure given in this may not give exact result. It is only given to understand concept of chromatography. Real analysis may be more complicated and depends on chromatography parameter.
Important Note: Procedure given in this may not give exact result. It is only given to understand concept of chromatography. Real analysis may be more complicated and depends on chromatography parameter.
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