If a development solvent of too high a polarity is used, all components in the mixture will move along with the solvent and no separation will be observed (Rf's will be too large). 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).
How does polarity affect TLC?
The more polar the compound, the more it will adhere to the adsorbent and
the smaller the distance it will travel from the baseline
, and the lower its Rf value. Eluent: the solvent or mixture of solvents (mobile phase) used to develop a TLC chromatogram (plate).
How does the polarity of the solvent affect TLC and column chromatography?
The polarity of the solvent which is passed through the column affects
the relative rates at which compounds move through the column
. Polar solvents can more effectively compete with the polar molecules of a mixture for the polar sites on the adsorbent surface and will also better solvate the polar constituents.
What is the result of applying too much compound to a TLC plate?
If too much of a compound is applied to a TLC plate (or its too concentrated),
the dot will streak across the plate or it can run into neighboring
…
What problem will result if the level of the developing solvent in the developing jar is higher than the applied spots on the TLC plate?
If the solvent level in the developing jar is deeper than the origin (spotting line) of the TLC plate,
the solvent will dissolve the compounds into the solvent reservoir instead of allowing them to move up the plate by capillary action
. Thus, you will not see spots after the plate is developed.
Is TLC plate polar or nonpolar?
This very polar stationary phase is paired with a relatively
nonpolar mobile
phase (an organic solvent or solution), in what is referred to as “normal phase” TLC.
What happens if you use a nonpolar solvent for TLC?
The solvent level has to be below the starting line of the TLC, otherwise the spots will dissolve away. … Non-polar solvents
will force non-polar compounds to the top of the plate
, because the compounds dissolve well and do not interact with the polar stationary phase.
Why is the choice of solvent important in chromatography?
Selectivity and solvent strength are the most important factors that
determine success or failure
of a chromatographic separation. … Solvent strength equalization helps to ensure that the separation data can be rationally compared over a similar time or volume.
How do you determine the best solvent for TLC?
The solvent should be
2–3 mm deep
so that the spotted sample and the line are not submerged. This ensures the sample does not dissolve into the solvent and travel up the TLC plate with the solvent.
What happens when you increase polarity of the TLC solvent?
When the polarity of the eluent is increased,
its ability to attract polar molecules is increased
. This means that it can better compete with the silica in attracting the aspirin, and the Rf value will be higher.
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.
What would be the result of applying too much compound to a TLC plate quizlet?
What will be the result of applying too much compound to a TLC plate?
The spots of various components will overlap to the point where the number of different components cannot be ascertained resulting in erroneous conclusions about separation
and/ or the purity of the sample.
Can two compounds have the same Rf value?
The larger an Rf of a compound, the larger the distance it travels on the TLC plate. … If two substances have the same Rf value,
they are likely (but not necessarily) the same compound
. If they have different Rf values, they are definitely different compounds.
Why is Rf less 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.
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 should the spots placed at least 5mm from the edge of the plate?
The lanes should not be placed too close to the edge (keep at least 5mm away from each edge), as it is not unusual for
solvent
to travel slightly “fast” at the edge where capillary action of the solvent is greater (Figure 2.24).
