Vegetal pigments

Procedure

• Place the chopped plant leaves into the mortar. Add a bit of ethanol and calcium carbonate and grind until the pigments dissolve in the ethanol.
• Prepare a filter using the funnel and filter paper, and filter the mixture from the mortar.
• Cut the chromatographic plate into a long rectangle, about 4×10 cm, and draw a line with the solution 1 cm from the bottom using the pipette.
• Place it in a beaker with ethanol without touching the point and let it rest so that the liquid travels up the plate to reach the top.
• Remove the plate and observe what has happened.

Theoretical explanation

When plants photosynthesize, they manufacture their ‘food’ from atmospheric CO₂ and use sunlight as their energy source. The various photosynthetic pigments capable of absorbing light are found in the leaves including chlorophyll A (blue-green), chlorophyll B (yellow-green), carotenes (yellow-orange), xanthophylls (yellow), and anthocyanins (pink). The aim of this experiment is to separate some of these pigments using the thin-layer chromatography technique.

Chromatography is a technique that allows for the separation of different components of a mixture by passing the sample through a stationary phase (in our case, the chromatographic plate) with the aid of a mobile phase (alcohol). The separation of pigments occurs because each compound moves through the plate at a different rate.