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Chromatography
Chromatography is a separation technique used to separate the different components in a
liquid mixture. There are different types of chromatographic techniques such as column
chromatography, TLC, paper chromatography, and gas chromatography. Paper chromatography
is one of the important chromatographic methods. Paper chromatography uses paper as the stationary
phase and a liquid solvent as the mobile phase. In paper chromatography, a spot of the mixture
is put on the paper and the paper is carefully dipped into a solvent. The solvent rises up
the paper due to capillary action and the components of the mixture rise up at different
rates and thus get separated from one another.
Materials Required:
Chromatographic chamber, Whatman filter paper strip, capillary tubes, measuring cylinder,
thread, isopropyl alcohol, mixture of red and blue inks, distilled water, glass rod,
scale and pencil
Procedure:
Take a Whatman filter paper strip and draw a line with a pencil above 2cm from one end.
Put a pencil mark at the centre of the line. Now take a capillary tube and dip it into
the beaker containing the mixture of red and blue inks.
Using the capillary tube, put a drop of the mixture of red and blue inks at the central
point of the line. Allow it to dry in open air.
Again take the mixture of red and blue inks using the capillary tube.
Put another drop on the same spot and dry it again so that the spot is rich in mixture.
Now take a piece of thread and tie the filter paper with it and suspend the filter paper
vertically in the chromatographic chamber containing the solvent, which is a mixture
of 80% isopropyl alcohol and 20% water. Make sure that pencil line remains about 1
cm above the solvent level. Keep the chamber undisturbed for some time.
Notice the rise in solvent along with the mixture of red and blue inks.
When the solvent has risen, you will notice two different spots of blue and red colours
on the filter paper. Take the filter paper out of the chamber and
mark the distance that the solvent has risen on the paper with a pencil. This is called
the solvent front. Dry the paper and put pencil marks in the
centre of the blue and red spots. Measure the distance of the solvent front
from the original line and the distance of the two spots from the original line.
Calculate the Rf values of the blue and red inks by using the formula.
Rf =