Paper Chromatography

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Paper Chromatography
Chromatography comes from the Greek word khromatos (color) and graphein (to write); i.e. paper chromatography is literally color writing on paper. This method tests the purity of compounds and identifies substances. This analytical process, despite having been replaced by the success of thin layer chromatography, still stands as a valuable teaching tool, and is nevertheless very common.

This method is very useful because not only is it a relatively quick process, but also requires only small quantities of materials. The substances being tested are first distributed between a stationary phase and a mobile phase. The stationary phase refers to a piece of high quality filter paper used for testing. The mobile phase references the developing solution that travels up the stationary phase, leaving the samples in its traces. The sample then separates according to two main concepts: how strongly the solution absorbs on the stationary phase versus how well they dissolve into the mobile phase.

This experiment also depends upon the polarity of the molecules, and how many are involved. When a colored sample is put through the stationary phase, the colors separate from the sample when one end of the paper is placed in a certain solvent. The solvent then diffuses the sample throughout the paper, leaving in its wake the dissolution of the various molecules in the same according to the polarities of the molecules and the solvent, respectfully. However, if the sample contains more than one color, it indicates that there is more than one molecule present. Due to the different chemical structures of each kind of molecule, each one will have a slightly different polarity, giving each molecule a different solubility level when placed in the solvent. The unequal solubility levels from the various colors in the sample cause different color molecules to leave traces of the solution at different spots as the solvent moves up the paper. The more soluble a...
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