Separation of photosynthetic pigments by chromatography

This lab will be assessed on Conclusion & Evaluation and Manipulative Skills.

Introduction

The photosynthetic pigments can be separated and identified by chromatography. The relative distances travelled by the various pigments depend on which solvent is used.

Aim

·  To separate and identify the photosynthetic pigments present in various plants.

·  To compare the photosynthetic pigments present in these plants.

Diagram

Method

  1. Cut a strip of chromatography paper so that it fits into a gas jar.
  2. Rule a pencil line across the strip of paper 3cm from one end.
  3. Using a mortar and pestle, grind up fresh leaves in pure propanone, producing as concentrated a pigment solution as possible. Filter the solution.
  4. Using a very thin capillary tube or the head of a pin, place a drop of the pigment solution at the centre of the pencil line. Allow it to dry and place a second drop on the first. Repeat this until you have built up a small concentrated spot of pigment.
  5. Pour some solvent into the gas jar to a depth of approximately 1.5-2cm. Place a lid over the gas jar so that the atmosphere inside becomes saturated with vapour.
  6. Place the bottom edge of the chromatography paper into the solvent so that it is just touching. Make sure that the pigment spot is not immersed.
  7. The solvent front will rise up the paper and separate the pigments. When the solvent is close to the top of the paper, remove the strip and rule a pencil line to mark the distance travelled by the solvent. Dry the paper.
  8. Identify the pigments by their colours and their Rf values.

Tasks

·  Carry out the method described above on the leaves of 3 different plants.

·  Record the raw data in an appropriate manner and present it clearly, allowing for easy interpretation.

·  Process the raw data and present it appropriately.

·  Draw valid conclusions and compare your results with literature values.

·  Evaluate the procedure used and suggest improvements to the method.

Conclusion and Evaluation (CE) / Concluding / Evaluating procedure(s) / Improving the investigation
c = 2 / States a conclusion, with justification, based on a reasonable interpretation of the data. / Evaluates weaknesses and limitations. / Suggests realistic improvements in respect of identified weaknesses and limitations.
p = 1 / States a conclusion based on a reasonable interpretation of the data. / Identifies some weaknesses and limitations, but the evaluation is weak or missing. / Suggests only superficial improvements.
n = 0 / States no conclusion or the conclusion is based on an unreasonable interpretation of the data. / Identifies irrelevant weaknesses and limitations. / Suggests unrealistic improvements.
Criteria / Aspect 1 / Aspect 2 / Aspect 3 / Grade
Manipulative Skills (MS) / Following instructions: / Carrying out techniques: / Working safely:
c = 2 / Follows instructions accurately, adapting to new circumstances (seeking assistance when required). / Competent and methodical in the use of a range of techniques and equipment. / Pays attention to safety issues.
p = 1 / Follows instructions but requires assistance. / Usually competent and methodical in the use of a range of techniques and equipment. / Usually pays attention to safety issues.
n = 0 / Rarely follows instructions or requires constant supervision. / Rarely competent and methodical in the use of a range of techniques and equipment. / Rarely pays attention to safety issues.