Chromatography: Paper Chromatography and its Uses

Introduction:

We have learned that most of the colors are made by blending two or more primary colors, such as orange color is prepared by mixing yellow and red.

So even though our eyes see a single color, it may be the result of one type of color or may be the blending of different colors.

For instance, different base colors or dyes are mixed together to make a black color ink.

We used to mix different colors with paints or play dough. It is easy to mix the colors and make a new color.  But today here we will focus on how to separate different colors from their mixture.

Explanation:

Chromatography

We use chromatography technique to separate the different colors in the dye. It can be used to separate the components of the mixture. Means it works when all the components in the mixture dissolved in one solvent

The term “chromatography”is derived from Greek, chroma meaning, “color,” and graphein meaning “to write.” Chromatography is one of the important process to separate chemical mixtures. It is technique used for the separation, purification, and testing of compounds.

As a separation method, chromatography has a number of advantages. It is capable of separating all the components of a multicomponent chemical mixture without an extensive knowledge of the identity, number, or relative amounts of the substances present.

Paper Chromatography

It is one of the important types of chromatography. Which involves placing a small dot or line of sample solution onto a strip of chromatography paper. If you are separating colored compounds like ink, dyes, or food coloring you can easily see the results by eye.

• The paper is placed in a container with a shallow layer of solvent and sealed.
• As the solvent rises through the paper, it meets the sample mixture, which starts to travel up the paper with the solvent.
• This paper is made of cellulose.

Chromatogram

A visible record (such as a graph) showing the result of separating the components of a mixture by chromatography is called a chromatogram.

Figure: Chromatogram of the green felt tip pen

From above chromatogram,

• We can say that it contains a mixture of dyes.
• Different dyes in ink travel through the chromatography filter paper at different speeds.
• The most soluble colors dissolve and travel further and faster than less soluble dyes which stick to the paper more.
• The blue dye goes up the paper.
• This might be because the blue dye dissolves better in the solvent.
• Or yellow dye sticks more strongly to the paper.

Paper Chromatogram of Spinach Leaves

Even though spinach leaves are green, there are actually many different colored molecules within spinach. By performing paper chromatography, we can see the different pigments.

• Chlorophylls​ are plant green pigments essential for the process of photosynthesis. Located in the chloroplasts of spinach leaves and other kinds of plants.
• Two types of these pigments, both chlorophyll a and chlorophyll b, are present in spinach leaves.
• Both types of chlorophyll reflect green light, which gives the pigments their green appearance.

Using Chromatography:

• We can determine the composition of a mixture. 
• Police forces uses gas chromatography to find out how much alcohol is in blood sample of driver.
• Detective uses chromatography to look for traces of explosives on the body hair of suspect bombers.

Summary

• Reversible change: A change that can happen backward, i.e., can be reversed is called a reversible change.
• Irreversible change: A change that cannot happen backward, i.e., it cannot be reversed is called an irreversible change.
• Chromatography: Chromatography is the technique for the separation, purification, and testing of compounds.
• Paper chromatography is a technique that involves placing a small dot or line of sample solution onto a strip of chromatography paper.
• The Chromatogram of the green felt tip pen shows that it contains a mixture of dyes.
• Paper chromatogram of spinach leaves: It shows different colored molecules within spinach (chlorophyll a and chlorophyll b).
• Chromatography is a vital tool used in many fields to determine the composition of a mixture.