Make sure the TLC plate is not touching the filter paper because the eluent of the filter paper can be absorbed by the adsorbent and eluent will come from the sides and not from the bottom. Make sure TLC plate is level in developing chamber or eluent will run up unevenly.
What can go wrong in TLC?
Examples of common problems encountered in TLC: The compound runs as a streak rather than a spot: The sample was overloaded. Run the TLC again after diluting your sample. Or, your sample might just contain many components, creating many spots which run together and appear as a streak.
It’s used to test for the presence of various materials, to monitor the rate and progress of a reaction or to determine the purity of a product. Filter paper impregnated with solvent is usually used to saturate the development chamber’s air with solvent vapor so the stationary phase doesn’t dry during the process.
Why is it important that the chromatography paper not touch the sides of the chromatography chamber?
Staple the paper so that the ends of the paper do not touch each other, because if they do, it will affect the flow of the solvent at that point.
Why do you use a pencil and not a pen to mark TLC plates? Answer: The pen ink becomes mobile on the plate and travels up the TLC plate with TLC solvent. But the solid particles of graphite in the pencil won’t get dissolved and hence can be used to mark TLC plates.
What does multiple spots on a TLC plate mean?
Ideally, each compound in a mixture will produce a distinct spot so a sample with two compounds will give two different spots, and so on. An important property of any compound, is its Rf-value (retention factor). In simple terms, this value is an indication of how far up a TLC-plate a compound has wandered.
How do I stop my TLC from streaking?
One way to remove the streaking is to add a few drops of ammonia (for amines) or formic acid (for carboxylic acids) to the eluting solvent.
(In ordinary paper chromatography, the paper is the stationary phase.) Pencil is always used to mark a chromatography paper because ink may run and interfere with the chromatogram. Do not allow the sides of the paper to touch the sides of the container as that can make the solvent front run crookedly.
Can you reuse chromatography paper?
With reversed-phase chromatography, column reuse is a given. Why, because the hydrophobic stationary phase is washable with organic solvents to remove highly retained contaminants and the columns can be stored in acetonitrile or methanol for long time periods.
How does the liquid rise through the filter paper?
Answer: By means of capillary action the liquid rise through filter paper.
What happens if the solvent front reaches the top of the plate?
Do not allow the solvent front to reach the top of the plate. That may cause erroneous Rf values and may cause spots that are close together to run into each other. Take the plate out with tweezers and mark the solvent front line with a pencil as soon as possible.
Explanation: In paper chromatography a filter paper is used as a stationary phase and the solvent for extraction is used as a mobile phase. The mobile phase moves slowly and takes along with it the components of the mixture to a distant where the components can be visualized easily.
What happens if you touch chromatography paper?
When you handle this paper, hold it only on one of the long (18.5 cm) sides, which will be considered the “top” of the sheet. The amino acids from your fingers will contaminate the paper and lead to erroneous results if it is touched on the “bottom”.
Why were you required to handle the chromatographic paper only at its corners?
Handle the paper only on the edges to avoid leaving fingerprints, as these may hinder the elution process.
What is the result of paper chromatography?
Paper chromatography is a method used by chemists to separate the constituents (or parts) of a solution. Different molecules run up the paper at different rates. As a result, components of the solution separate and, in this case, become visible as strips of color on the chromatography paper.
You can’t use a pen because the ink will travel up the TLC plate with the TLC solvent, just like your chemical samples do. You can only spot/label/mark TLC plates using a pencil. The graphite in a pencil will not run up the plate!
Why do the spots on a TLC plate appear dark under UV light?
The most common non-destructive visualization method for TLC plates is ultraviolet (UV) light. If a compound absorbs 254nm UV light, it will appear dark, as the compound prevents the fluorescent material from receiving the UV light.
Why is ink never used for drawing the baseline?
A baseline is drawn in pencil on the chromatography paper. (Not in ink, as the ink may get separated in the experiment and interfere with the results). A small spot of the mixture is placed on the baseline. The paper is then removed from the solvent, and marked to show where the solvent got up to.
