Activity Corner: Chromatography

3 min read

Is black ink truly black? There is more than what meets the eye in the colours of ink. Some inks are made of several different individual coloured components, and it gives us the final ink colour that we see when mixed together.

Chromatography is a technique that we can use to separate the components of an ink sample. This technique makes use of the difference in solubility (ability to dissolve) of the components. Let us explore chromatography with a simple activity!

What you will need:

  1. Coffee filter paper (cut into a rectangle)
  2. A stick
  3. Some scotch tape
  4. A glass container
  5. Water
  6. Ink sample

Step One: Prepare your sample

Place a small spot of your ink sample on one end of your coffee filter paper. Here, we used black ink.

Step Two: Set up your chromatography apparatus

Use scotch tape to tape the other end of your filter paper to the stick, then use the stick to suspend your filter paper above the bottom of the container as shown. Then fill your glass with a little amount of water. 
Note: The water level should reach the end of your filter paper, but not your ink spot!

Step Three: Wait for the chemistry to happen

As the water creeps up the filter paper, it will eventually reach your ink spot, and you will see your ink spot start to smear across the paper as it travels upwards with the water. If your ink is made of several components, you should start to see the components separate.
Note: If your ink spot does not smear, this means your ink is insoluble in water. Try a different ink!

Step Four: Check your results

Remove your filter paper from the glass and observe the ink smear. In our example here, we can see a blue component at the bottom, while at the top we have blue, red, black and a little bit of green. This shows us that the initial black ink actually has at least 5 different components in it.

You can repeat this experiment with another ink sample, and compare the results.

How does it work?

The experiment done here is a form of chromatography known as paper chromatography. Water creeps up the filter paper via capillary action, where it eventually reaches the ink spot. The ink spot is then dissolved in the water and travels upwards together with the waterfront. Within the ink, less water-soluble components travel a shorter distance, while more water-soluble components travel a greater distance. 

Uses of Chromatography

These days, paper chromatography has been replaced by more accurate forms of chromatography, such as high-performance liquid chromatography (HPLC). One use of modern chromatography methods is in food and drink tests, where scientists are able to identify the components in food and drink, to check if it is safe to consume.

Written by Raphael Ng
Illustrated by Lim Daphne

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