Pigment Separation in Allium cepa

by | Aug 13, 2022 | Physics, Experiments


In this experiment(Pigment Separation in Allium cepa), we will be determining among the eluting solutions such as petroleum ether, water, and acetone, which can seclude the colour pigment in red onions.


To find out which eluting solution can separate the colour pigment in red onions.


1. Rf stands for Retention Factor.

2. The Rf value of the pigment is equal to the distance travelled by the pigment from the origin divided by the distance travelled by the solvent from the origin.


1. Red Onions

2. Acetone

3. Petroleum Ether

4. Distilled Water

5. Chopping Board

6. Distilled Water

7. Plastic Gloves

8. Cotton Yarn

9. Plastic Gloves

10. Plastic Bags

11. Filter Paper

12. Triple Beam Balance

13. Beaker

14. Watch Glass

15. Glass Bottles

16. Graduated Cylinder

17. Pipettes

18. Petri Dishes

19. Wash Bottle

20. Scissor

21. Compass

22. Ruler

23. Notebook


Step 1: Prepare the chromatography papers.

Step 2: Prepare red onion extract.

Step 3: Put solvents (petroleum ether, acetone, and water) in Petri dishes.

Step 4: Spot chromatography papers.

Step 5: Observe the movement of pigment in each of the solvents.

Step 6: Record your observations.

Step 7: Perform two experimental batches for each of the three trials, which included petroleum ether, water, and acetone as eluting solutions.

Step 8: Perform four more spots for each of the papers.

Step 9: After drying the papers, note and measure the pigment movement.

Step 10: Now, tabulate, graph, compute and analyze the Rf values of each of the pigments.

Chromatography Papers


1. From our experiment, we observed that petroleum ether showed no movement of pigments. On the other hand, water and acetone showed the movement of pigments.

2. From the visual analysis of all chromatography papers, we observed that the two pigment colours, purple and yellow, moved in water and acetone.

3. In water dishes, the Rf value of yellow pigment lies between the range of 0.075 and 0.625, with a mean of 0.174.

4. In water dishes, the Rf value of purple pigment lies between the range of 0.875 and 0.975, with a mean of 0.932.

5. Only yellow colour pigment moved in three of the six acetone dishes. There, it had an Rf value that ranged between 0.800 and 0.975. It acquired a mean of 0.454.


1. The pigment got separated into two pigment colours. This includes yellow (quercetin) and purple (anthocyanin).

2. From the movement of pigments in all the six trials in the water eluting solution, we concluded that the pigments are polar in nature.

3. Acetone eluting solution moved the yellow pigment in three among six of the trial; this indicated the weakly polar nature of pigments.


1. Handle the eluting solutions with care.

2. Record your observation carefully.


In this experiment, we determined the movements of coloured pigment in three of the eluting solutions.

Viva Questions With Answers

Q.1 What was the aim of your experiment?

ANS. We aimed to determine among the eluting solutions, such as petroleum ether, water, and acetone, which can separate the colour pigment in red onions.

Q.2 In which eluting solution pigments showed polar nature?

ANS. In the water eluting solution, pigments showed polar nature.

Q.3 Which eluting solution showed the weak polar nature of pigments?

ANS. Acetone showed the weak polar nature of pigments.

Q.4 Which eluting solution showed no motion of pigments?

ANS. Petroleum ether elution solution showed no motion of pigments.


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