What is RF Value? The Rf (retardation factor) value is the ratio of the solute’s distance travelled to the solvent’s distance travelled. The word comes from chromatography when it was discovered that a given component will always travel the same distance in a given solvent under the same conditions.
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How do you calculate the Rf value?
Why do we calculate Rf values?
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.
How do you calculate Rf in paper chromatography?
To calculate an Rf value, divide the distance travelled by the component – in other words, the distance from the starting pencil line to the coloured spot -by the distance travelled by the solvent. Rf values are important because each component has a fixed Rf value under a specific set of conditions.
How do you calculate Rf values for pigments?
- Rf for carotenes = 9.7cm/9.8cm = 0.99.
- Rf for xanthophylls = 7.2cm/9.8cm = 0.73.
- Rf for chlorophyll a = 5.1cm/9.8cm = 0.52.
- Rf for chlorophyll b = 3.7cm/9.8cm = 0.38.
What is the Rf value for sample 1?
How do you find Rf values with multiple spots?
How does Rf value relate to polarity?
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 do you interpret Rf values?
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.
How do you calculate molecular weight from Rf values?
Use a graphing program, plot the log (MW) as a function of Rf. Generate the equation y = mx + b, and solve for y to determine the MW of the unknown protein. Run the standards and samples on an SDS-PAGE gel. Process the gel with the desired stain and then destain to visualize the protein bands.
Why is the Rf value always less than 1?
Because the mobile phase (the solvent) is faster than the stationary phase (the pigments).
How do you calculate Rf value in chromatography GCSE chemistry?
What 2 distances are important when calculating Rf values in chromatography?
By definition, the Rf value is taken as the distance from the centre of te zone. This is however prone to visual estimation errors, so the best way to calculate the centre is to measure the following 2 distances: measurment from origin to the top edge of the zone, measurment from origin to the bottom edge of the zone.
What is the relationship between Rf value and solubility?
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 is the maximum Rf value for any molecule in paper chromatography?
Size of spot may range 2-5 mm depending upon number of sample to be applied to the paper. The mobile phase which gives Rf value range between 0.2-0.8 are selected for chromatographic work.
Can two compounds have the same Rf value?
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.
How do you find the Rf value of an amino acid?
The Rf value can be calculated by measuring the distance of the substance from its starting point in millimeters, as well as the distance the solvent traveled from its starting point in millimeters, then dividing the substance distance by the solvent distance.
What factors affect the Rf values?
Retention Factor 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.
Why does a more polar solvent increase Rf values?
Given two compounds that differ in polarity, the more polar compound has a stronger interaction with the silica and is, therefore, more capable to dispel the mobile phase from the binding places. As a consequence, the less polar compound moves higher up the plate (resulting in a higher Rf value).
How do you calculate the polarity index of a solvent?
One way you could actually calculate a solvent’s polarity is by using its dielectrict constant, which is used to measure how well the solvent can partly cancel the field strenght of the electric field of a particle added to it. The higher the value of a solvent’s dielectric constant, the more polar it will be.
Are Rf values constant?
The symbol Rf stands for “retardation factor” or “ratio-to-front”. It is expressed as a decimal fraction. When the conditions are duplicated, the same average relative positions will turn up for the solvent and solute; thus the Rf value is a constant for a given compound.
What is a good Rf value?
A desirable Rf value lies between 0.3 and 0.7, since it is likely that other compounds present in the mixture will be visible on the TLC plate when the Rf is in this range.
What is the relationship between Rf value and molecular weight?
A linear relationship exists between the logarithm of the molecular weight of native nucleic acid, and its Rf. The Rf is calculated as the ratio of the distance migrated by the molecule to that migrated by a marker dye-front.
Does Rf value indicate molecular weight?
Using a solution of standard molecular weight styrene, Rf values coan be found to correlate with molecular weights. Higher molecular weights will not diffuse as far up the TLC plate as low molecular weights, therefore, approximate molecular weights can be determined by comparison to the standards.
What is Rf value in SDS-PAGE?
The Rf is defined as the migration distance of the protein through the gel divided by the migration distance of the dye front. The distance should be measured from the top of the resolving gel to the band of interest, as illustrated on the gel.