How to Calculate RF

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In paper chromatography, RF stands for retention factor, or the distance a liquid compound travels up a chromatography plate. The chromatography paper is the stationary phase and the liquid compound is the mobile phase; the liquid carries the sample solutions along the paper. When a liquid travels up the paper, it separates, allowing the person studying it to decipher the different components of the liquid solution. All compounds have a specific RF value for every specific solvent, and RF values are used to compare unknown samples with known compounds. Calculating RF is relatively simple with the right materials.

Calculating Retention Factor

    Dip a strip of chromatography paper into the liquid solvent and the liquid solution to be analyzed. As the solvent is absorbed up the paper, the components of the solution will bleed out onto the paper.

    Once the liquids have stopped moving, take the paper out of the liquid.

    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. The retention factor will always be between zero and one. It cannot be zero because the substance must have moved, and it cannot be more than one because the solution cannot travel farther than the solvent.

    Use the retention factor to compare to known retention factors and determine the substance with which you are working.



About the Author

Erin Clyburn has been writing professionally since 2004. She has been published in "The Progressive Farmer" magazine, Pearson's "Student Book of College English" textbook and Birmingham's "Lipstick" magazine. She holds a Bachelor of Arts in English literature from Mississippi State University, and is pursuing a Master of Arts in children's literature from Hollins University.

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