C1.3 - separating photosynthetic pigments (4b)

Question 1

what happens during TLC if pigments are not soluble?

Answer 1

pigments that are not soluble in the extraction solvent are not added to the dots at the origin and do not move, so they are absent from the chromatogram

Question 2

what are characteristics of pigments with a higher Rf value?

Answer 2

• more soluble in the solvent
• often smaller
• have a lower affinity with the solid phase material on the TLC plate

Question 3

what does the unique combination of pigment concentration depend on?

Answer 3

• which pigments are present
• relative concentrations

Question 4

what is the process of separating photosynthetic pigments by chromatography?

Answer 4

1. extract photosynthetic pigments by crushing leaves in a suitable solvent
2. small concentrated dots of extract are made towards the bottom of the TLC plate
3. the solvent moves up the TLC carrying the pigments
   - pigments move at different rates depending on their solubility and separate
4. measure the distances travelled by the solvent front and each pigment
5. calculate the Rf value: distance moved by pigment / distance moved by solvent front
6. identify the pigments by comparing Rf values to known values, or using pigments colours