Watch a mixed spot separate in real time as solvent climbs the paper strip.
Paper chromatography separates a mixture into its individual components based on a simple physical principle — different substances travel at different rates through the same stationary phase — and calculating the resulting Rf value is a standard AP Chemistry Unit 3 analytical technique.
As solvent climbs a paper strip by capillary action, each dissolved substance in a spotted mixture is carried along at a rate determined by its relative affinity for the stationary phase (the paper itself, or more precisely the water trapped in its cellulose fibers) versus the mobile phase (the moving solvent). Less polar substances, which interact more weakly with the polar paper and more strongly with a less polar solvent, travel farther and faster; more polar substances cling more tightly to the paper and lag behind.
The retention factor, Rf = (distance traveled by the spot) / (distance traveled by the solvent front), is a normalized value between 0 and 1 that should, in principle, be reproducible for a given substance under fixed solvent and paper conditions — making Rf values useful for identifying unknown components by comparison to known standards run under the same conditions.
Chlorophyll extraction is a classic worked example: a leaf pigment extract separates into several visibly distinct bands with characteristically different Rf values — carotene (the least polar pigment, giving carrots their orange color) travels farthest and shows the highest Rf, followed by chlorophyll a, then chlorophyll b, with xanthophyll (the most polar, oxygen-containing pigment) traveling the shortest distance and showing the lowest Rf. This consistent ordering, driven entirely by relative polarity, is one of the most commonly performed real chromatography labs in introductory chemistry courses.
Black ink separation demonstrates the same principle on a mixture most people don't realize is a mixture at all — common black ink is actually a blend of several different dyes, each with distinct polarity, which paper chromatography visibly resolves into individual colored bands.
This chromatography simulator animates the separation in real time as solvent climbs the paper, calculates Rf values live for each component, and includes real pigment and ink datasets — turning a physical wet-lab technique into a repeatable, instant interactive demonstration.