Separation and Identification of Plant Pigments by TLC Main
Separation and Identification of Plant Pigments by TLC Main
Separation and Identification of Plant Pigments by TLC Main
No: Date:
Aim: To separate and identify plant pigments from spinach leaves using TLC.
Introduction:
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EXP. No: Date:
better separations, and the choice between different stationary phases. Because of its
simplicity and speed TLC is often used for monitoring chemical reactions and for the
qualitative analysis of reaction products.
The solvent will move up the plate by capillary action, which occurs as a result of the
attraction of solvent molecules to the silica gel and the attraction of solvent molecules to
one another. As the solvent moves up the plate, it carries along any substances dissolved in
it, in this case pigments. The pigments are carried along at different rates because they are
not equally soluble in the solvent and because they are attracted to different degrees, to the
silica gel.
The order of pigments top to bottom on the silica gel slide following chromatography
is different than in paper chromatography. The colors are the same—carotenes (yellow to
yellow-orange to brown), chlorophyll a (bright green to blue-green), chlorophyll b (yellow-
green to olive green), and xanthophylls (yellow).
Figure 2. Different forms of hydroxyl group that can occur on the surface of silica gel.
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EXP. No: Date:
Materials Required:
Fresh spinach leaves; Motor and pestle; TLC plates (Pre- coated plates); TLC chamber;
Solvents: Acetone, chloroform, petroleum ether.
Procedure:
1. Homogenize 50 g fresh spinach with 50 mL 100% acetone using a mortar and pestle.
2. Filter to remove debris using layers of folded over cheesecloth.
3. Readjust volume of filtrate to 40 mL (if necessary).
4. Pour filtrate (green liquid) into a separatory funnel.
5. Carefully, pour 60 mL petroleum ether down the sides of the separatory funnel. Gently
rotate the separatory funnel. You should now have two layers, petroleum ether (with
the dissolved pigments) on top, and the acetone on the bottom.
6. Drain off the lower layer of acetone into a designated waste beaker. Stop the separation
at about the layer line.
7. Add 50 mL of distilled water to the pigment mixture (in the remaining petroleum ether)
by carefully pouring the water down the sides of the funnel.
8. Rotate slowly until the upper layer contains nearly all of the chlorophyll. Gas pressure
will rise in the funnel—vent carefully.
9. After the layers separate, drain off the lower layer of water (with traces of acetone) and
discard into the waste beaker. The upper layer of petroleum ether should contain all of
the pigments.
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EXP. No: Date:
10. Add 50 mL distilled water to wash the petroleum ether and remove any traces of
acetone. Repeat this wash a second time. During the final wash, when removing the
acetone, also remove a few milliliters from the upper layer line.
11. Remove 5 mL of the petroleum ether-chlorophyll layer and put it in a small test tube.
Allow to evaporate down to get a very concentrated extract. This is the chlorophyll
extract to be used for silica gel chromatography.
12. Pour about 1 cm of solvent (9:3:3—petroleum ether: acetone: chloroform) in a 100 mL
beaker. Cover the 100 mL beaker with a 400 mL beaker to create a chromatographic
chamber. Let it stand for a few minutes to saturate the chamber with the solvent.
13. Obtain two TLC plates, and with pencil, mark a straight line across the plate 1 cm from
the edge.
14. Using a capillary tube, place about 10 drops of the extract in the center of the silica gel
plate about 2 cm from the bottom. We do not want this pigment mixture to come in
direct contact with the solvent mixture!
15. Slowly place the silica gel plate in the solvent and immediately cover the 100 mL beaker
with a 400 mL beaker to create a chromatographic chamber.
16. When the eluent is 1 cm from the top of the TLC sheet, use forceps to remove the sheet
from the chamber. Immediately draw a faint pencil line to mark the position of the
solvent front.
17. Allow the sheet to dry and with a pencil lightly outline all visible spots. The spots may
fade or change colors after exposure to air and light.
18. Beginning at the origin, label all spots as A, B, C, D, etc. and calculate their Rf values.
19. Try to identify the pigments by their colors.
20. After about 10- minutes, remove the silica gel plate, take a picture of the plate with the
digital camera (don't forget your scale!), and measure distances of solvent and pigment
from the initial placement point to determine the Rf values for each pigment. The colors
of the main pigments are the same as in paper chromatography; however, as you will
find out, the Rf values should be different.
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EXP. No: Date:
Distance
Distance of
Color of the of Rf
Chromatogram pigment Pigment identified
pigment solvent value
(mm)
(mm)
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8
9
10
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Result: