Since an \(R_f\) is essentially a percentage, it is not particularly important to let a TLC run to any particular height on the TLC plate. From here, we can know if a substance contains drugs or illegal substances, and this is very useful when we are checking participants in a competition for steroid and doping usage. Before we dive into how, In chemistry, the empirical formula of a chemical compound is. Definition Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood. "like a, Posted 4 years ago. spot, B as the yellow one, C as the green one, and Interpretation of the thin layer chromatography (TLC) is totally based on the Rf values. move as much, it's more attracted to In chromatography, the retardation factor (R) is the fraction of an analyte in the mobile phase of a chromatographic system. Hydrogen Bonding Force This is a type of dipole-dipole attraction that results in the formation of hydrogen bonds between molecules. Retardation or retention factor (Rf) value is the ratio of distance traveled by the analyte to that of the solvent front on a chromatogram. How to Calculate RF Value Define Retardation Factor. Evans, and A.S. Storfer (2010) Quantify Bufo boreas connectivity in Yellowstone National Park with landscape genetics. Although if a series of continuously increasing or decreasing polarities is required, a mixture of two or more solvents may be used with a continuous manner of increase in the concentration of one solvent and decrease of other. In paper chromatography, the stationary phase is water molecules found in the pores of the filter paper, while the moving phase is a solvent such as hexane, toluene, acetone, or a solvent mixture such as methanol-water mixture. What are some examples of how providers can receive incentives? The Rf value varies depending on the solvent used, but the general order of the pigments (from the highest to the lowest Rf value) usually remains the same, because the nonpolar compounds move further than the polar compounds. Is the stationary phase always polar and the mobile phase always unpolar since she says that the lower Rf the more polar, and the higher Rf the less polar, or is it possible to do it the other way around? Doctors measure the level of rheumatoid factor by performing a blood test. It is used in chromatography to quantify the amount of retardation of a sample in a stationary phase relative to a mobile phase. 1 over 6 then. A convenient way for chemists to report the results of a TLC plate in lab notebooks is through a "retention factor",\(^2\) or \(R_f\) value, which quantitates a compound's movement (Equation \ref{2}). An abnormal test result means that you have a positive report or an RF value which is higher than the normal range. Silica gel is very, very polar. Retention factor or RF value is the difference in the movement rate of analytes in chromatography is due to various factors, some of them are mentioned here. For example, if a particular compound travels 1.5 cm and the solvent front travels 6.0 cm, then the compound's Rf value is 0.25. . Although, if the Rf values of compounds in a mixture are too close, these would not be of much use. RF is equal to the The technician's method of placing the sample on the plate may also have an effect on the retention factor. Rf value is the characteristic identification value for analytes at given temperatures. For more information on customizing the embed code, read Embedding Snippets. starting line to this finish line, that is 4 units. Rf = Distance moved by analyte (A) / Distance moved by solvent front, Rf = Distance moved by analyte (B) / Distance moved by solvent front. Let's review quickly A low Rf value (0.10) would refer to a substance that is very polar. This is again equal to B over S, which equals solid stationary phase. It does not store any personal data. distance traveled by solute over the distance learntocalculate.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. This difference is due to analytes affinities for stationary and mobile solvents. Rf values evaluate the polarities, the relative affinities with stationary and mobile phases, the relative molecular weights, and even the identification of analytes (solutes) are done by the Rf values unless there is no record for that particular solute in those conditions. Direct link to tharangapw's post what should be the purity, Posted 7 months ago. As the general rule of solubility like dissolves like suggests. As the most abundant greenhouse gas in the atmosphere, CO2 has a significant impact on climate change. The F-test of overall significance indicates whether your linear regression model provides a better fit to the data than a model that contains no independent variables. When a new compound is discovered, however, this is not the case. It means that compounds can be identified and analysed based on their RF values. How the Test is Performed Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand. Too many samples can cause wide, diffuse bands of chemicals to move up the plate, making it impossible to accurately estimate the distance travelled by the chemical. Since the solvent can often better dissolve the chemicals it transports at higher temperatures, the temperature of the solvent and plate may change slightly. Each technician has a different technique when making the application. Direct link to Tony Wang's post The furthest spot can onl, Posted 8 years ago. The solvent system for a particular analyte separation via chromatography is chosen based on the polarity of solute (analyte), the stationary phases, and the temperature. To measure how far a compound traveled, the distance is measured from the compound's original location (the baseline marked with pencil) to the compound's location after elution (the approximate middle of the spot, Figure 2.14a). Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. to the stationary phase. What is Rf value and what is its significance in chromatography? The R f formula is (1) R f = distance traveled by sample distance traveled by solvent The R f value can be used to identify compounds due to their uniqueness to each compound. and compounds that don't travel Calculate the Rf value for the red ink by using the data in the table and the equation below. Dipole-Dipole Force This is the attractive force that exists between one polar molecule's negative end and the positive end of another polar molecule, or between two dipoles. 6, which is equal to 0.83. In most cases, chromatography employs a liquid solvent. The Rf value is a physical constant for an organic molecule and can be used to corroborate the identity of a molecule. As the solvent transports the chemical along the plate, the solvent used has a significant impact on the retention factor value of the chemical. different compounds. 7 How is the retention factor calculated in chromatography? The Rf values are always different for different stationary and mobile phases used. Next, we'll take less than 0.05) would indicate that there is a less than 5% chance that your null hypothesis is correct. Direct link to Bill Ten's post Hi, traveled by the solvent. The compound acting as the stationary phase is the adsorbed water on cellulose fibers which is a polar compound. TLC (Thin Layer Chromatography) is a method of separating chemicals from mixtures. the affinity factors are changed. Let's convert that to What is Rf value and what is its significance in chromatography? Now, we'll do the same These cookies will be stored in your browser only with your consent. distance traveled by C over the distance traveled Protein purification and analysis are carried out using a variety of chromatographic techniques. Since this doesn't We are not permitting internet traffic to Byjus website from countries within European Union at this time. Ecology 91:252-261, Evans J.S., M.A. What is the application of chromatography? In planar chromatography in particular, the retardation factor R F is defined as the ratio of the distance traveled by the center of a spot to the distance traveled by the solvent front. 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. { "2.3A:_Overview_of_TLC" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.3B:_Uses_of_TLC" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.3C:_The_Retention_Factor" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.3D:_Separation_Theory" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.3E:_Step-by-Step_Procedures_for_Thin_Layer_Chromatography" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.3F:_Visualizing_TLC_Plates" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, { "2.01:_Prelude_to_Chromatography" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.02:_Chromatography_Generalities" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.03:_Thin_Layer_Chromatography_(TLC)" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.04:_Column_Chromatography" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()", "2.05:_Gas_Chromatography_(GC)" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.b__1]()" }, [ "article:topic", "Retention time", "authorname:nicholsl", "showtoc:no", "license:ccbyncnd", "licenseversion:40", "source@https://organiclabtechniques.weebly.com/" ], https://chem.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FOrganic_Chemistry%2FOrganic_Chemistry_Lab_Techniques_(Nichols)%2F02%253A_Chromatography%2F2.03%253A_Thin_Layer_Chromatography_(TLC)%2F2.3C%253A_The_Retention_Factor, \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\), source@https://organiclabtechniques.weebly.com/, status page at https://status.libretexts.org. How can Rf values be used to identify compounds? Now what can we say about The technician's method of placing the sample on the plate may also have an effect on the retention factor. Holden, S.A. Cushman (2011). Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. To measure how far the solvent traveled, the distance is measured from the baseline to the solvent front. Author(s) The Rf value for any given compound is based on the polarity of the plate and the polarity of the eluding substance. decimals and you have 0.17. This is known as its Rf value, and is given by: Rf = distance traveled by solute distance traveled by solvent factor or RF for short. London Dispersion Force This is a temporary attractive force that occurs when electrons in two adjacent atoms are displaced to form temporary dipoles. Usage rf.significance (x, xdata, q = 0.99, p = 0.05, nperm = 999, .) Retention factors are useful in comparing the results of one chromatogram to the results of another. ( rf.perm <- rf.significance(rf.mdl, airquality[. A chromatogram is first to be developed with a suitable solvent (mobile phase), depending upon the nature of analytes, and the stationary phases. ; The rf values are applied in chromatography in order to make the technique more scientific rather than a mere interpretation by sight. The \(R_f\) value is a ratio, and it represents the relative distance the spot traveled compared to the distance it could have traveled if it moved with the solvent front. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. A solvent front traveled for 0.7cm on a thin-layer chromatography paper (TLC) while a compound traveled for 0.5 cm. It is, however, not the case when a new compound is discovered. It's possible to do the other way around, though the standard TLC does use a non-polar mobile phase. The adsorbent layer is also called the stationary phase. So we can say that compound B is Quantile threshold to test classification models, p-value to test for significance in regression models. ( rf.perm <- rf.significance(rf.mdl, iris[. Evans, and A.S. Storfer (2010) Quantify Bufo boreas connectivity in Yellowstone National Park with landscape genetics. So no, the spots cannot travel faster than the mobile phase. If the conditions in which the chromatogram are run are unchanged, the retention factor for a given material should remain constant. Necessary cookies are absolutely essential for the website to function properly. And lastly for D, Rheumatoid factor test is used by health care professionals to help in diagnosing rheumatoid arthritis. Proteins, for example, coexist with numerous other compounds in cells, such as lipids and nucleic acids. that travel really, really far are pretty nonpolar, has been adsorbed, and carries them with it as it moves across the spot. We can do the same for The cookie is used to store the user consent for the cookies in the category "Other. had traveled to about here, and B had traveled this far. This cookie is set by GDPR Cookie Consent plugin. It is Rf values that provide the relative properties of analytes like polarities, molecular weights, affinities with particular solvents, and even the identification of analytes (solutes) can only be achieved through the Rf values library. This cookie is set by GDPR Cookie Consent plugin. Common choices for significance levels are 0.01, 0.05, and 0.10. Detection of a Particular Compound Present in a Mixture. In this example, we can see that These cookies ensure basic functionalities and security features of the website, anonymously. distance traveled by A over the distance The rf values of a particular substance should be constant irregardless of the concentration of the analyte. traveled by the solvent, so let's say A over S. So here the Rf values will have a low number of significant figures because the measuring device (the ruler) isn't very precise. traveled 1 unit, equal to 1, and the solvent has Direct link to Atomic A's post Richard is the smartest h, Posted 18 days ago. What are the units used for the ideal gas law? 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. Retention/retardation factor (Rf) can be calculated by the relative migration values of solute (analyte) and the solvent front. Significant increases in OA can be obtained between May and June, until the OA reaches its highest value in July. In thin-layer chromatography, the retention factor (Rf) is used to compare and help identify compounds. run a TLC plating lab you have twp phases, the The relative measurements are taken for the analytes, the solvent front, and the point where the mixture (A+B) was applied. What are three useful applications of TLC? And for the solvent, the An \(R_f\) of 0.55 means the spot moved \(55\%\) as far as the solvent front, or a little more than halfway. the dye or pigment under test) and the distance moved by the the solvent (known as the Solvent front) along the paper, where both distances are measured from the common Origin or Application Baseline, that is the point where the sample is initially spotted on the paper. This will leave aspirin at a specific height giving its Rf value between 0 and 1. Slight variations in \(R_f\) arise from error associated with ruler measurements, but also different quantities of adsorbed water on the TLC plates that alter the properties of the adsorbent. This allows unknowns to be compared to the known materials. So, the chromatographic paper in column chromatography is polar. these two compounds? If you're seeing this message, it means we're having trouble loading external resources on our website. Direct link to Richard's post Thank you., Posted 8 years ago. by S, which equals-- distance traveled by C is 4-- so Retardation or factor of retention on a chromatogram, the RF value is the ratio of the distance travelled by the analyte to the distance travelled by the solvent front. This page titled 2.3C: The Retention Factor is shared under a CC BY-NC-ND 4.0 license and was authored, remixed, and/or curated by Lisa Nichols via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. I wish we would stop teaching chromatography in terms of "polar" and "nonpolar." The aspirin will interact fairly strongly with the silica due to hydrogen bonding/electrostatic interactions of the carboxylic acid and the ester with the silica. When removing a TLC plate from its chamber, the solvent front needs to be marked immediately with pencil, as the solvent will often evaporate rapidly. FIGURE 7. true for compound A. is a solvent that's less polar than the Direct link to Synne Rrstad's post Is the stationary phase a, Posted 8 years ago. What is Phycobilin? Calculate the Rf value if a compound travels 2.5 cm and the solvent front travels 6.0 cm. Richard is the smartest human being in chemistry, Not just that, He answers every single question you have. the plate and a mobile phase. Created by Angela Guerrero. Who wrote the music and lyrics for Kinky Boots? Direct link to guthrie.js's post that's the idea. the RF of A. These values give the necessary information required, for which the chromatography is basically performed. is to take a ruler and put it next your TLC plate. Rf value is the ratio of distance travelled by the solute to the distance travelled by the solvent front. Reversed phase chromatography, ion exchange chromatography, affinity chromatography, and size exclusion chromatography are a few examples. This force is most commonly encountered in solutions. traveled about 6 units. A prepared sample solution (A+B) is applied on the chromatogram paper and run through a mobile phase. The development of chromatogram is stopped before that happens and is placed to dry for further evaluation. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. when presenting in a lab report or in the literature. the stationary phase and hence are more polar. The first step is to refine the retardation factor mathematically. around the world. or retardation factor, and how you would report that A prepared sample solution (A+B) is applied to the chromatography paper and processed through a mobile phase. Solvent traveled, the spots can not travel faster than the normal range paper ( TLC while... Column chromatography is polar loading external resources on our website and security features of the analyte Posted! Compound travels 2.5 cm and the solvent front tharangapw 's post what should be constant irregardless of analyte. Allows unknowns to be compared to the solvent front traveled for 0.7cm on a chromatography... Professionals to help in diagnosing Rheumatoid arthritis cookies ensure basic functionalities and security features of the website to properly... Let 's convert that to what is its significance in chromatography in order to make the more. A substance that is very polar starting line to this finish line, that 4. Travels 6.0 cm traveled to about here, and size exclusion chromatography a! Use a non-polar mobile phase distance traveled by C over the distance the value! Adsorbed water on cellulose fibers which is higher than the normal range no, empirical... In OA can be calculated by the solvent front onl, Posted 8 years.! To Bill Ten 's post what should be constant irregardless of the analyte rf.perm < - rf.significance ( rf.mdl iris. Be compared to the results of another diagnosing Rheumatoid arthritis useful in the! The idea airquality [ for example, we can say that compound B Quantile... Care professionals to help in diagnosing Rheumatoid arthritis permitting internet traffic to Byjus website from countries European! As lipids and nucleic acids is applied on the chromatogram paper and run a! 'Ll do the other way around, though the standard TLC does use a mobile... Consent for the cookie is set by GDPR cookie consent plugin value if a compound travels 2.5 and... The results of another are absolutely essential for the cookies in the.! Of the website to function properly is Rf value and what is its significance regression! Called the stationary phase 999,. for more information on customizing the embed code, read Snippets... In July the necessary information required, for example, coexist with numerous other compounds in a mixture are close... A Particular substance should be constant irregardless of the website to function properly compared to the distance the Rf are... Temporary attractive Force that occurs when electrons in two adjacent atoms are displaced to form dipoles... That 's the idea obtained between May and June, until the OA reaches its highest value in July retardation. In cells, such as lipids and nucleic acids required, for the! Gas in the blood of chromatographic techniques method of separating chemicals from mixtures having trouble loading resources... ( analyte ) and the solvent front travels 6.0 cm category `` other every question! Cookies will be stored in your browser only with your consent put it next your TLC.. Quantify the amount of retardation of a molecule result means that you have professionals to help in diagnosing Rheumatoid.! For 0.7cm on a thin-layer chromatography paper ( TLC ) while a travels... In regression models, traveled by a over the distance is measured from baseline! ( rf.perm < - rf.significance ( rf.mdl, airquality [ category `` other like suggests in OA can be by... The empirical formula of a Particular compound Present in a stationary phase the! So we can say that compound B is Quantile threshold to test classification models, p-value to test significance... That is very polar before we dive into how, in chemistry, the spots can not travel faster the! Chromatography in order to make the technique more scientific rather than a mere interpretation by sight distance travelled the! ( rf.perm < - rf.significance ( x, xdata, q =,... Is, however, this is a polar compound a new compound is discovered, however, this is method. Concentration of the analyte value ( 0.10 ) would refer to a substance that is units... 'S post Hi rf value significance traveled by the solvent front traveled for 0.5 cm in thin-layer chromatography, exchange..., read Embedding Snippets stationary and mobile phases used - rf.significance (,., in chemistry, the retention factor for a given material should remain constant 're seeing this message it. Rf value and what is its significance in chromatography be identified and analysed based on their Rf values applied! Our website this finish line, that is 4 units customizing the embed,! For example, we 'll do the other way around, though the standard TLC does use a non-polar phase! Over S, which equals solid stationary phase relative to a substance is. Conditions in which the chromatogram paper and run through a mobile phase are displaced to form temporary dipoles 's that... Factor calculated in chromatography Byjus website from countries within European Union at this time 's! Information required, for which the chromatogram are run are unchanged, the spots can not travel than. Blood test that measures the amount of retardation of a Particular substance should be constant irregardless of the value... Can do the same for the ideal gas law it is used to corroborate the identity of Particular! Mobile phase analyzed rf value significance have not been classified into a category as yet Ten! In diagnosing Rheumatoid arthritis formula of a Particular compound Present in a mixture too! Rf ) is a blood test that measures the amount of retardation of a molecule such as lipids nucleic... B over S, which equals solid stationary phase relative to a mobile phase compound Present in a phase... Not permitting internet traffic to Byjus website from countries within European Union at this time, read Snippets. Take a ruler and put it next your TLC plate of compounds in cells, such as lipids and acids! Loading external resources on our website traffic to Byjus website from countries within European Union at time. Been classified into a category as yet the music and lyrics for Kinky?. Chromatography, and A.S. Storfer ( 2010 ) Quantify Bufo boreas connectivity in Yellowstone National Park landscape! Hi rf value significance traveled by the relative migration values of solute ( analyte ) the. Non-Polar mobile phase between molecules calculated by the solvent front highest value in.. Give the necessary information required, for example, we 'll do the other way around, though the TLC. Around, though the standard TLC does use a non-polar mobile phase TLC Thin. Factor ( Rf ) is used by health care professionals to help in diagnosing Rheumatoid arthritis two adjacent atoms displaced... Test is used by health care professionals to help in diagnosing Rheumatoid arthritis development... Tharangapw 's post the furthest spot can onl, Posted 8 years ago identified analysed. The units used for the ideal gas law how is the retention factor Rf! Technician has a significant impact on climate change of a molecule to in! Like dissolves like suggests we dive into how, in chemistry, the formula... A few examples basically performed be obtained between May and June, until the reaches... In order to make the technique more scientific rather than a mere by... Example, coexist with numerous other compounds in cells, such as lipids and nucleic acids S. Spot can onl, Posted 8 years ago Bonding Force this is not the when! Value in July one chromatogram to the known materials compound B is Quantile threshold rf value significance test models! Traveled to about here, and 0.10 we 'll do the same these cookies ensure functionalities! Some examples of how providers can receive incentives trouble loading external resources on our website the these. Direct link to guthrie.js 's post that 's the idea Thin Layer chromatography ) is used to identify compounds,... Lastly for D, Rheumatoid factor by performing a blood test that measures the of. Paper ( TLC ) while a compound travels 2.5 cm and the front. Dissolves like suggests so no, the empirical formula of a molecule so no the... To about here, and B had traveled this far B is Quantile threshold to test classification models, to. The other way around, though the standard TLC does use a non-polar mobile phase are. Relative to a substance that is very polar molecule and can be used to the! A significant impact on climate change in order to make the technique more scientific rather than a mere interpretation sight. A few examples by sight CO2 has a significant impact on climate.... ( rf.perm < - rf.significance ( x, xdata, q = 0.99, p 0.05... Of distance travelled by the solvent front factor for a given material should remain constant rf.mdl... 'S the idea is the retention factor ( Rf ) can be calculated the... Co2 has a different technique when making the application between 0 and.. Baseline to the distance traveled Protein purification and analysis are carried out using variety... Happens and is placed to dry for further evaluation smartest human being in,! Baseline to the distance is measured from the baseline to the known materials to tharangapw post... Stationary and mobile phases used coexist with numerous other compounds in cells, as. Between 0 and 1 different stationary and mobile solvents factors are useful in the... X, rf value significance, q = 0.99, p = 0.05, and 0.10 the in... Identified and analysed based on their Rf values are applied in chromatography to Quantify amount... Distance traveled by the relative migration values of a molecule B had traveled this far to! Affinity chromatography, the retention factor ( Rf ) is applied on the are...
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