Table of Contents
- 1 Why would Rf values be different?
- 2 What factors affect Rf values in paper chromatography?
- 3 Why different compounds in TLC plate have different Rf values?
- 4 Should Rf values be reproducible under what conditions?
- 5 Why is it necessary to equilibrate the developing chamber before chromatography?
- 6 Why is it necessary to cover the developing chamber during the TLC development?
Why would Rf values be different?
The larger an Rf of a compound, the larger the distance it travels on the TLC plate. When comparing two different compounds run under identical chromatography conditions, the compound with the larger Rf is less polar because it interacts less strongly with the polar adsorbent on the TLC plate.
What factors affect Rf values in paper chromatography?
Factors affecting Rf value in paper chromatography
- The solvent system.
- Composition of the mobile phase.
- The working temperature of the system.
- The quality of the paper used.
- The distance through which the solvent runs.
- The quality and nature of solvents used.
- The polarity of components.
- The pH of the solvent or mobile phase.
Why is it important to saturate the chamber before introducing the TLC plate?
You want your chamber air thoroughly impregnated with solvent vapor in TLC because this keeps the stationary phase from drying out before the process is finished. If the stationary phase dries out prematurely, the components in the sample won’t separate properly and your results will be incorrect.
Why do substances move at different rates in TLC?
Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile. Polar molecules will be more strongly attracted to polar solvents, and so would move further if a polar solvent was used as opposed to a non-polar solvent.
Why different compounds in TLC plate have different Rf values?
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).
Should Rf values be reproducible under what conditions?
Rf values are therefore not exactly reproducible from one experiment to another, even if an effort is made to carry them under the exact same conditions. When comparing two or more substances, they must be run simultaneously on the same plate or the comparison is invalid.
What is the retention factor in chromatography?
However, in column chromatography, the retention factor or capacity factor (k) is defined as the ratio of time an analyte is retained in the stationary phase to the time it is retained in the mobile phase, which is inversely proportional to the retardation factor.
What is the retention factor in paper chromatography?
The retention factor (Rƒ) may be defined as the ratio of the distance travelled by the solute to the distance travelled by the solvent. It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase.
Why is it necessary to equilibrate the developing chamber before chromatography?
At all time there is an equilibrium state between all 3 of them. if you do not equilibrate your tank prior to developing the plate then this equilibrium will take place during development itself. this will strongly effect the development.
Why is it necessary to cover the developing chamber during the TLC development?
It is extremely important that the solvent in the developing chamber be lower than the spotos on the plate, because the solvent must be drawn upward through the sample in order to draw the sample along with it. Finally it is important to cover the chamber to be sure that the solvent does not evaporate.
Why do some substances not move up the chromatography paper?
Because they spend more time dissolved in the stationary phase and less time in the mobile phase, they aren’t going to travel very fast up the paper. The tendency for a compound to divide its time between two immiscible solvents (solvents such as hexane and water which won’t mix) is known as partition.
Why do different solvents give different chromatograms?
Chromatography is a technique used to separate the components of a mixture. Different solvents will dissolve different substances. A polar solvent (water) will dissolve polar substances (water soluble ink in the video below).