1. Prepare a developing chamber by adding 15-20 ml of solvent
2. Place the TLC plates in the chamber so that they do not touch. Allow the
solvent to rise to within one cm of the top of the plates.
3. Remove the plates, mark the solvent front using pencil, and allow them to dry.
4. Visualize the spots by illumination under a UV lamp.
5. Trace around each spot with a pencil and then measure the distance traveled by
each component.
6. Calculate the Rf by dividing the distance of the solvent front by the distance of the
spot. The Rf value is characteristic of each substance and may be used for
identification of the substance.
Constraints
During this experiment there are a few constraints that must be taken into account such as:
Time – I only have a few hours to complete this whole experiment therefore, I must make the method as sort as I possibly can maybe not including some unnecessary things or maybe drying the TLC paper in a oven.
Equipment – I only have a limited supply of apparatus so I cant use equipment that is to expensive or too big, heavy to handle or that I need training for.
These constraints must be taken into account before I begin my method.
Task 2
Preparation of analgesics
To prepare the analgesics you must do the following:
- Take a quarter tablet of your chosen analgesic.
- Crush the tablet using a pestle an mortar
- Add 1cm³ of methanol
- Continue to crush the tablet with the pestle and mortar until the analgesic is dissolved in the methanol
- Pure the analgesic solution into a container
Ensure you use a separate pestle mortar an contain to prepare your analgesic to prevent cross contamination.
Identification of an unknown analgesic
- On your Thin layer Chromatography plate, draw a 1 cm line from the bottom (IN PENCIL)
- Using your prepared samples and a capillary tube apply the samples along the 1cm line you must though
- ensure all samples are equally spread apart (around 1cm)
- ensure the spots are as small as possible
- and apply each sample 5 times to the spot
- Examine the plate under a ultraviolet light to see if you have added enough analgesic, if not add more
- prepare the developing chamber using a large beaker (big enough to fit your TLC plate) and place a watch glass on the top (preventing the solvent evaporating)
- place under 1cm³ of solvent in the beaker (around ½ cm³) ensuring it does not pass your 1cm line and the spots on it.
- Let the solvent rise up the plate
- Before the solvent reaches the top of the plate, remove the plate from the beaker and mark the solvent front (in pencil)
- Allow the plate to dry.
While the plate is drying you should prepare the visualisation part of the experiment
- Take a container which has a secure lid
- Place a few iodine crystals in
When the plate has dried:
- Place the plate into the container until the spots have become visible
- Draw the outlines of each spot.
- Using a suitable table record the Rf values of each spot.
- Repeat the experiment but using a different solvent
Health and safety
All solvents must be handled in a fume cupboard (including iodine crystals).
All solvents are flammable
Wear correct PPE while handling solvents
I found that no procedures or techniques needed to be modified during the course of this experiment. I found the method given was very accurate and I was able to follow it very easily with out any problems.
During the experiment I was very conscious of the time I had and because of which I found examining the plate under the ultraviolet light, as it could remove the possibility of not adding enough sample an therefore decrease the possibility of inaccurate Rf values resorting in me having to repeat the whole experiment.
With me able to ensure I had enough sample I was able to complete the experiment twice with different solvents
Task 3
Results
Solvent 1 – Ethlacetate
The unknown analgesic Rf value matches the Rf value of paracetamol.
Solvent 2 – Dichloroethaneacetic acid
The unknown analgesic Rf value matches the Rf value of the paracetamol
Therefore, my results indicate that the unknown analgesic is paracetamol
Conclusion
My objective to complete was to conduct an experiment to discover what a unknown analgesic was using 4 known analgesics. I feel I have successfully completed this objective and identified that the unknown analgesic is paracetamol.
Evaluation
I found that my results were accurate, as I later did find out the unknown analgesic was infact paracetamol. So I therefore evaluate that my experiment was a complete success. I would not change my method as I feel it is accurate enough to give the correct Rf values to get an accurate result.
I feel the accuracy of this experiment was very good although I do not know the actual % of inaccuracy that could arise during the experiment