Table of Contents
- 1 How do components move on the TLC plate and why?
- 2 Why do different compounds travel different distances on chromatography paper?
- 3 Why do pigments have different mobility on TLC plates?
- 4 What happens if the spots are made too small when preparing a TLC plate for development?
- 5 What determines how far a pigment will travel in chromatography?
- 6 What is the maximum Rf value for any molecule in paper chromatography?
- 7 Why silica gel is used in TLC?
- 8 Why do TLC spots have to be small?
- 9 Why do molecules take longer to move up a TLC plate?
- 10 Where does the solvent have to be in TLC?
- 11 How is a TLC plate developed in a beaker?
How do components move on the TLC plate and why?
The stronger a compound is bound to the adsorbent , the slower it moves up the TLC plate. Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
Why do different compounds travel different distances on chromatography paper?
Why do the different pigments travel to different distances in paper chromatography? (KN) (Answer: The different pigments are attracted differently to molecules in the paper and to the solvent molecules. So they travel at different speeds up the paper and so in a given time, some will travel further than others).
Which compound traveled the farthest on the TLC plate?
Benzoic acid is the most polar molecule, so it would travel the shortest distance, and be closer to the bottom of the TLC plate. Naphthalene is the least polar molecule, so it would travel the farthest.
Why do pigments have different mobility on TLC plates?
Different compounds should move different distances on your TLC plates; however the exact distance a particular compound moves depends on how far the solvent is allowed to rise up the plate. The further the solvent moves, the further the spots travel.
What happens if the spots are made too small when preparing a TLC plate for development?
What happens if spots are made too small when preparing a TLC plate for development? What happens if spots are made too large when preparing a TLC plate for development? Why must the spots be above the level of development solvent in chamber? They will dissolve in the development solvent if they were submerged.
What is the principle of TLC?
Thin-layer chromatography is a method of separation or identification of a mixture of components by using finely divided adsorbent Solid/ liquid over a glass plate and liquid as a mobile phase. Separation of adsorbed substances by the mobile phase.
What determines how far a pigment will travel in chromatography?
The speed at which a particular pigment moves depends on its relative affinities for the two solvent phases; if it has no affinity whatever for the water phase, it will travel at maximum speed, just behind the solvent-front (eg beta-carotene); on the other hand, if the pigment has no affinity whatever for the non-polar …
What is the maximum Rf value for any molecule in paper chromatography?
Size of spot may range 2-5 mm depending upon number of sample to be applied to the paper. The mobile phase which gives Rf value range between 0.2-0.8 are selected for chromatographic work.
What happens if a TLC plate is allowed to develop too long?
Chemicals move up a TLC plate along with the solvent being used to develop the plate. This means that if left long enough, the chemicals will all merge together at the top of the plate, eliminating any separation that you could have seen on the plate.
Why silica gel is used in TLC?
Silica gel is by far the most widely used adsorbent and remains the dominant stationary phase for TLC. The surface of silica gel with the highest concentration of geminal and associated silanols is favored most for the chromatography of basic compounds because these silanols are less acidic.
Why do TLC spots have to be small?
Spots are applied to the plate using very thin glass pipettes. The capillary should be thin enough to apply a neat spot, but not so thin as to prevent the uptake of an adequate quantity of analyte. Here is a popular method of producing TLC pipettes.
Why silica is used in TLC?
Why do molecules take longer to move up a TLC plate?
Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile. Likewise, the polarity of the molecules can affect how far the spots travel, depending on the type of solvent used.
Where does the solvent have to be in TLC?
The solvent level has to be below the starting line of the TLC, otherwise the spots will dissolve away. The lower edge of the plate is then dipped in a solvent.
How does TLC work in relation to chromatography?
TLC functions on the same principle as all chromatography: a compound will have different affinities for the mobile and stationary phases, and this affects the speed at which it migrates. The goal of TLC is to obtain well defined, well separated spots.
How is a TLC plate developed in a beaker?
A TLC plate can be developed in a beaker or closed jar (see picture below). Place a small amount of solvent (= mobile phase) in the container. The solvent level has to be below the starting line of the TLC, otherwise the spots will dissolve away. The lower edge of the plate is then dipped in a solvent.