What does it mean to have a high RF value?
Definition. Rf = distance traveled by substance/distance traveled by solvent front. 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.
The retention factor (Rƒ) may be defined as the ratio of the distance traveled by the solute to the distance traveled 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.
- It is defined as the process of separation of the individual components of a mixture based on their relative affinities towards stationary and mobile phases. Principle: The samples are subjected to flow by mobile liquid onto or through the stable stationary phase.
- The farther a compound travelled, the larger it's Rf value. Logically, you can conclude that if a compound A travels farther than compound B in a polar solvent, then it is more polar than solvent B. So basically, the compound that is more "like" the solvent will have the larger Rf value.
- In chromatography, the retardation factor (R) is the fraction of an analyte in the mobile phase of a chromatographic system. In planar chromatography in particular, the retardation factor Rf is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front.
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.
- Chlorophylla-a is the primary pigment for photosynthesis in plants, but the range of light absorption is extended by chlorophyll-b, beta-carotene and other accessory pigments. The variations of chlorophyll-b and the bacterial version are indicated above.
- Green light is the least effective for plants because they are themselves green due to the pigment Chlorophyll. Different color light helps plants achieve different goals as well. Blue light, for example, helps encourage vegetative leaf growth. Red light, when combined with blue, allows plants to flower.
- Trees do not live forever. They do age and eventually die. Some live much longer than others though, and it turns out that some of the longest living trees survive best in the more extreme climates and situations. For example the oldest living tree in the US is over 5000 years old.
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.
- The stronger a compound is bound to the adsorbent , the slower it moves up the TLC plate. 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).
- Thus, simple paper chromatography can be used to identify substances both qualitatively (by color) and quantitatively by its characteristic Rf value. If distance from the origin to solvent front is 6 cm, calculate the Rf factor for the 4 pigments illustrated above. Start with the pigment that rose the highest (5.5 cm).
- With your ruler, measure the distance the solvent traveled, which is Df, and measure the distance the test solution traveled, which is Ds. Calculate the retention factor using this equation: RF = Ds/Df. Simply divide the distance the solution traveled by the distance the solvent traveled.
Updated: 2nd October 2019