The mobile phase rises up by the capillary action. The testing sample is concentrated as a minute spot at the bottom of the filter paper. When the mobile phase which is a liquid, rises up in the filter paper the spotted mixture is gradually rises with the mobile phase. This eventually leads to the separation of the compounds. Compounds in the mixture will be separated according to their ability of the solubility. In other words it is again the polarity as in open column chromatography. More polar substances will move slower and less polar substances will travel faster. Consider “A” substance is more soluble than “B” in the stationary phase, thus “A” will dissolve in that solvent. This means “A” is more polar than “B” with respect to the stationary phase solvent. Thus “A” will travel slowly than “B”. And “B” will elute first. This explains that substances that having more solubility in stationary phase move slower and substances having less solubility in stationary phase move faster.
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