Why is a small spot of pigment needed on the TLC plate? Use a different solvent and/or a different stationary phase, this means pigments which may have run together will separate out.Considering this, why is only a small spot of pigment needed on the TLC plate?
Use a different solvent and/or a different stationary phase, this means pigments which may have run together will separate out.
One may also ask, why is it recommended to spot the analyte on the TLC plate? Why is it recommended to spot the analyte on the TLC plate in a position that it will not be immersed in eluent solvent? If the sample is above the solvent surface, the solvent rises through say capilliary action and flows over the point where the sample has been applied so the process can work.
Secondly, does a single spot on TLC guarantee a single substance?
!!! No ; pure' must see 1 spot but if its 1 spot it is not necessary pure. TLC is typically used to determine the correct adsorbent and solvent for column chromatography.
Why is UV light used in TLC?
Using UV light to identify spots( compounds) on a TLC plate is very common as it is an easy and non-destructive method. Most TLC plates have Zinc sulfide, which makes the TLC plates appear green under short wavelength UV. The oragnic compounds which absorb the UV light appear dark.
What happens if you apply too much compound on the TLC plate?
Answer: The ink might travel with the eluting solvent and separate into its component pigments, giving you a lot of extraneous spots. 3) What could happen if you spot too much of a compound on the TLC plate? Answer: The spot would show trailing. Answer: The spots would dissolve into the reservoir of eluting solvent.What is Rf value?
The Rf value is defined as the ratio of the distance moved by the solute (i.e. the dye or pigment under test) and the distance moved by the the solvent (known as the Solvent front) along the paper, where both distances are measured from the common Origin or Application Baseline, that is the point where the sample isIs it possible to distinguish two spots that have the same Rf value?
5- Yes, it is possible to distinguish two spots that have the same Rf value but represent different compounds.What does TLC tell you about purity?
Thin Layer Chromatography (TLC) is a separation technique requiring very little sample. It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate. In addition, tentative identification of the unknown compound can be made through TLC analysis.What makes a compound UV active and appear on a fluorescent TLC plate?
The silica gel manufacturer coats the silica gel on the TLC plate with a material that fluoresces (illuminates) green under ultraviolet (UV) light (more specifically 254 nm light). To be UV-active compounds must possess a certain degree of conjugation, most commonly aromatic compounds.Is silica polar or nonpolar?
silica gel is very polar. so more polar material moves more slowly than nonpolar material, which feels less attraction from the silica gel. it's used in TLC and column chromatography (not paper chromatography).What will be the appearance of a TLC plate of a solvent of too low polarity?
If the solvent is of too low a polarity the components will not move enough, and again separation will not occur (Rf's will be too small). Note that the spotting solvent is simply used as a vehicle to transfer the material to be analyzed to the TLC plate. Once the transfer is made the spotting solvent evaporates.What will happen if the spots on the TLC plate come in contact with the eluent?
By capillary action, the solvent will immediately start rising up the TLC plate. As soon as it comes into contact with the spots, it will cause the less polar components of the mixture to start moving.What happens if the spots on the TLC plate are made too large when preparing the plate for development?
What happens when the spots are made too large when preparing a TLC plate for development? If the spot too large it may cause the shape of the final spot become skewed and elongates.Why should a TLC plate be removed before the solvent reaches the top?
TLC. Allow the solvent to climb up the TLC plate, and remove the plate when the solvent nearly reaches the top. Quickly, before the solvent evaporates, mark the solvent front.What should be used to spot the sample into a TLC plate?
A capillary spotter (microcapillary) should be use to spot the sample onto a TLC plate.Is eluent the same as mobile phase?
Eluent. The eluent or eluant is the "carrier" portion of the mobile phase. It moves the analytes through the chromatograph. In liquid chromatography, the eluent is the liquid solvent; in gas chromatography, it is the carrier gas.What happens if the solvent line reaches the top of your TLC plate?
Chemicals move up a TLC plate along with the solvent being used to develop the plate. However, if the solvent reaches the top of the plate, the chemicals continue to move up.Why is it necessary to run TLC in a closed container?
It is necessary to run TLC in a closed container and have the interior saturated with the solvent vapor to ensure maximum resolution between components and to prevent solvent evaporating off. If the solvent evaporates off, the Rf value would be lower than the expected value.Why must the spot be applied to the TLC plate above the level of development solvent?
Why must the spot applied to a TLC plate be above the level of the developing solvent? The level of solvent or eluent must be below the level of the spots. Otherwise, the compounds will simply dissolve in the solvent and there will not be any spots left.Are RF values unique to a compound?
Rf or Retention factor is a unique value for each compound under the same conditions. The Rf for a compound is a constant from one experiment to the next only if the chromatography conditions below are also constant: solvent system. adsorbent.Can an RF value be greater than 1?
By definition, Rf values are always less than 1. An Rf value of 1 or too close to it means that the spot and the solvent front travel close together and is therefore unreliable. This happens when the eluting solvent is too polar for the sample. 
