Theory:

Chromatography is a significant biophysical technique for qualitative and quantitative analysis that allows for the isolation, identification, and purification of the components of a mixture.
 
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Colours
 
The word chromatography is derived from the Greek word kroma means "colour." This technique was given this name as it was first used to separate colours.
The technique of chromatography is being used to separate solutes that dissolve in the same solvent.
There are many types of chromatography techniques. Let us see about paper chromatography in brief.
Paper chromatography is a chromatographic method for separating chemical mixtures into their constituent compounds. The paper used in this process is made of cellulose.
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Paper chromatography
 
Paper chromatography is divided into two phases: A mobile phase and a stationary phase. Paper is the stationary phase, and the solvent is the mobile phase.
  
Three factors that determine the components' ability to travel with the solvent:
  • The sample molecule's polarity. Non-polar components move faster than polar components.
  • The adhesive nature of the sample molecule to the solvent or combination of solvents.
  • The silica and the sample are attracted to each other.
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Separation through chromatography
  
The compound mixture passes through the stationary phase with the mobile phase and separates based on the degree of adhesion (on the paper) of each component in the sample or compound mixture.
Example:
Lets us now check if the black ink stain is only a single colour?
 
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Placing a small drop of water-soluble ink.
 
Step 1: Take a thin strip of filter paper.

Step 2: With a pencil, draw a line approximately \(3cm\) above the lower edge.
 
Step 3: Place a small drop of water-soluble ink (from a sketch pen or fountain pen) in the middle of the line. Allow some time for it to dry.

Step 4: Lower the filter paper into a pan, bottle, beaker, or test tube filled with water until the ink drop on the paper is just above the waterline, then leave it alone.
 
Step 5: As the water rises to the top of the filter paper, keep an eye on it.
 
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Significant rise in the colour.
 
Observation: There is a significant rise in the colour from its initial point.
 
Result: Water is the solvent in our pigment, and the dye is soluble. The dye particles are carried along by the rising water on the filter paper.
 
A dye is usually a combination of two or more colours. The coloured part that is more soluble in the water rises faster, separating the colours.
Applications:
  • Colours in a dye can be separated using this method.
  • Natural pigments can be separated using this method.
  • Medicines derived from blood can be separated.
Chromatography