What is a good RF value?
The best Rf (retention or retardation factor) lies between 0.3 and 0.7. If you want the Rf of your TLC spot to be smaller, i.e., the spot to be lower down on the plate, you must decrease the eluent polarity.
What does the RF value tell you?
The Rf values indicate how soluble the particular pigment is in the solvent by how high the pigment moves on the paper. Two pigments with the same Rf value are likely to be identical molecules. Small Rf values tend to indicate larger, less soluble pigments while the highly soluble pigments have an Rf value near to one.
What does a high RF value mean?
A high Rf (Ie 0.92) would refer to a substance that is very non-polar. Ie that substance moved a 92% of the entire distance the solvent traveled. A low Rf value (0.10) would refer to a substance that is very polar. IE that substance was only able to move 10% of the entire distance the solvent traveled. Term.
How do you find the RF value?
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).
Why is RF useful?
R f values can be used to identify unknown chemicals if they can be compared to a range of reference substances. The Rf value for a particular substance is always the same if the same solvent and stationary phase are used.
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 factors affect the RF values?
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.
What do different RF values mean?
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.
What are the RF values of pigments?
|Pigment||Rf value range||Relative position|
|Carotene||0.89-0.98||Very close to the solvent front|
|Pheophytin a||0.42-0.49||Below the top yellow, above the greens|
|Pheophytin b||0.33-0.40||Below the top yellow, above the greens|
|Chlorophyll a||0.24-0.30||Above the other green, below the grey|
What does a small RF value indicate?
A small Rf indicates that the moving molecules are not very soluble in the hydrophobic (non-polar) solvent; they are larger and/or have a greater affinity for the hydrophillic paper (they have more polar groups) than molecules with a larger Rf.
What is the maximum and minimum value of RF?
In chromatography, the Rf value represents the ratio between the migration distance of a substance and the migration distance of the solvent front. Rf is a coefficient called retention factor and has values that range between zero and 1.
What is full form RF?
Radio frequency (RF) is a rate of oscillation in the range of about 30 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals.
Does a higher Rf value mean more polar?
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). Non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value).
Is RF value a percentage?
Rf values do not have units since it is a ration of distances. Because mixture solvents are often applied Rf values are usually written as the following examples: Rf = 0.66 (60% Ethanol) – if % is given it is assumed that the mixture is in water hence 60% ethanol 40% water.