If the compound is soluble in the solvent, it will travel further up the TLC plate. How well the compound likes the stationary phase.
If the compound likes the stationary phase, it will stick to it
, which will cause it to not move very far on the chromatogram.
What factors determine how far a solute will travel up a TLC plate?
The outcome depends upon
a balance among three polarities – that of the plate, the development solvent and the spot material
. If the development solvent is polar enough, the spot will move some distance from its original location.
What affects the distance Travelled in chromatography?
The distance travelled relative to the solvent is a constant for a particular compound as long as you keep everything else constant –
the type of paper and the exact composition of the solvent
, for example. The distance travelled relative to the solvent is called the R
f
value.
Do more polar solvents travel further in 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 solvent affect Rf value?
What is the liquid property responsible for the solvent climbing up the TLC plate?
The silica gel binds to the solute and the development solvent tries to dissolve it away, carrying the solute(s) along as the solvent travels up the plate. A
balance of intermolecular forces
determines the position of equilibrium and thus the ability of the solvent to move the solute up the plate.
How does TLC choose solvent system?
The choice of solvent or a mixture of solvents used in TLC is solely guided by two important factors : (a) the nature of the constituent to be separated i.e., whether it is polar or non-polar ; and (b) the nature of the process involved i.e., whether it is a case of ‘adsorption’ or ‘partition chromatography’.
How do you determine the best solvent for TLC?
The most suitable solvent system is the one that
moves all components off the baseline with Rf values between 0.15 and 0.85 (ideally, close to 0.2 – 0.4)
. Remember that it is not always possible in TLC but should be possible in flash chromatography where solvent gradients can be used.
How does solubility affect chromatography?
Higher the solubility of the constituents in the mobile phase, faster will be the mobility rate. Hence, the solubility of the components of the mixture affects the process of chromatography as
higher the solubility in the mobile phase, faster the components will elute out of the chromatography stationary phase
.
Why is water not a suitable solvent in paper chromatography?
Because the kind of compounfds that you try to determine using paper chromatography (organic compounds) are usually not soluble in water
. Furthermore, water could react chemically with some of this compounds, because it’s a very reactive molecule. You need organic solvents that are mostly inert.
What is solvent front in chromatography?
In chromatography, the solvent front is
the position on the TLC plate indicating the furthest distance traveled by the developing solvent (or eluent)
What phase is the solvent in chromatography?
Phases. Chromatography relies on two different ‘phases’: the
mobile phase
is the solvent that moves through the paper, carrying different substances with it. the stationary phase is contained on the paper and does not move through it.
What pulls the solvent mobile phase up the TLC plate stationary phase )?
After the sample has been applied on the plate, a solvent or solvent mixture (known as the mobile phase) is drawn up the plate via
capillary action
. Because different analytes ascend the TLC plate at different rates, separation is achieved. The mobile phase has different properties from the stationary phase.
Which of the TLC solvents below is most polar?
Which of the TLC solvents below is most polar? Answer:
Acetone is a more polar solvent than is hexanes
. If it were used to elute the same three compounds, each of the compounds would travel faster because the more polar eluting solvent is more proficient at eluting the compounds from the polar adsorbent.
Why do more polar solvents elute faster?
A polar solvent will compete well with molecules and will occupy sites on the stationary phase
. This will force compounds into the mobile phase, and result in faster elution/increased travel distance.
Does changing the solvent change the Rf value?
absolutely ; this due to different in interaction between the sample and mobile phase
. also we have the similar things with the stationary phase . so you can see different Rf of the same molecule in different solvent ratio.
When should a mixed solvent system be used for TLC explain?
Use a mixed solvent system
when no single solvent gives the desired separation
. Mixed solvent systems can be particularly effective for separating compounds having similar physical properties. The order of elution for TLC is about the same as for column chromatography.
What would be the result of failing to mark the solvent front after developing a TLC plate would this affect your ability to calculate component Rf values Why or why not?
Failure to mark the solvent line on the developed TLC plate would result in
not being able to measure the distance traveled by the solvent
. This would affect your ability to calculate Rf values because the formula requires that information.
Why is it important to mark the solvent front with a pencil?
Why is there a need to mark the solvent front? …
The solvent begins to evaporate at the moment the TLC chamber is opened
. I mark the desired solvent front on both paper and tlc plates, and it matters for both how long it takes for the solvent to reach the mark, since the distance is a proxy for the time.
What happens if the solvent line reaches the top of your TLC 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.
Why is the choice of solvent important in chromatography?
If a solvent is not polar enough, no compounds will elute from the column
. Proper choice of an eluting solvent is thus crucial to the successful application of column chromatography as a separation technique.
Why should you not change solvents abruptly when running a column?
This
will impact the efficiency of the separation of compounds negatively
. The stationary phase will dry out which again can lead to “column cracking” or unevenness which will impact the eluding of the compounds.
What factors affect separation in chromatography?
The factors effective on this separation process include
molecular characteristics related to adsorption (liquid-solid), partition (liquid-solid), and affinity or differences among their molecular weights
[1, 2].
How do you select a chromatography solvent?
Selection of solvents requires a balancing act between solvent and compound polarities. For most separations,
the solvent should be less polar than the compounds
. The compounds must also be soluble in the solvent so they are not permanently adsorbed.
