What is Rf value in TLC?
In thin-layer chromatography, the retention factor (Rf) is used to compare and help identify compounds. The Rf value of a compound is equal to the distance traveled by the compound divided by the distance traveled by the solvent front (both measured from the origin).
What does Rf value tell you about polarity?
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.
Why do you think a same component will have different Rf values when different solvents are used?
In general, low polarity compounds have higher Rf values than higher polarity compounds. In general, the adsorptivity of compounds increases with increased polarity (i.e. the more polar the compound then the stronger it binds to the adsorbent). The eluting power of solvents increases with polarity.
How does polarity affect retention factor?
Retention Factor When comparing two different compounds under the same conditions, the compound with the larger Rf value is less polar because it does not stick to the stationary phase as long as the polar compound, which would have a lower Rf value.
What Rf values mean?
RF value (in chromatography) The distance travelled by a given component divided by the distance travelled by the solvent front. For a given system at a known temperature, it is a characteristic of the component and can be used to identify components.
Should Rf values be reproducible?
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 are 3 factors that can affect Rf values in TLC?
Rf values and reproducibility can be affected by a number of different factors such as layer thickness, moisture on the TLC plate, vessel saturation, temperature, depth of mobile phase, nature of the TLC plate, sample size, and solvent parameters. These effects normally cause an increase in Rf values.
What does a low Rf value mean?
distance traveled. by the spot. 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.
Why are Rf values important?
Retention factors are useful in comparing the results of one chromatogram to the results of another. If the conditions in which the chromatogram are run are unchanged (same mobile and stationary phases), the retention factor for a given material should remain constant.