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Introduction

Separations in paper chromatography involve the same principles as those in thin layer chromatography. In paper chromatography, like thin layer chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is usually a piece of high quality filter paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate on the stationary phase according to how strongly they adsorb to the stationary phase versus how much they dissolve in the mobile phase. In all types of chromatography, the sample is placed on one end of a tube or plate which contains an inert material called a stationary phase, and a solvent, called the mobile phase, flows over it. The fundamental principle of chromatography is the equilibrium that forms when a compound is either dissolved in a mobile phase or absorbed on a stationary phase. ...read more.

Middle

(Evaporation would affect the Rf). This process of separation of the components is referred to as eluting (or developing) the chromatogram. The experiment is allowed to proceed uninterrupted until the solvent begins to approach the top of the paper. It must not be allowed to reach the top of the paper, otherwise separated components may again catch up with each other and recombine at the top. To stop the chromatogram, the paper is simply removed from its container and dried to remove the mobile phase. In paper chromatography, when you place a colored chemical sample on a filter paper, you can get the colors to separate from the sample by placing one end of the paper in a solvent. As the solvent diffuses up the paper, it dissolves the various molecules in the sample according to the polarities of the molecules and the solvent. If the sample contains more than one color, that means it must have more than one kind of molecule. ...read more.

Conclusion

water, ethyl alcohol, and hexane. As the liquid moves up the paper, the molecules of the sample mixture will also move. Polar molecules within the sample will spend most of their time bound to the polar surface of the paper and will therefore not move very much. Nonpolar molecules, however, will spend most of their time dissolved in the liquid as it moves up the paper. When the liquid reaches the top of the paper, these molecules will also have traveled most of the way to the top. The two types of molecules (polar and nonpolar) are now separated. The choice of the eluent or solvent is the most difficult task. Choosing the right polarity is critical because this determines the level of separation that will be achieved ( this degree of separation helps one to identify the constitute molecules). Common solvents used in chromatography, in order of increasing polarity, are: petroleum, ether or hexanes, cyclohexanes, toluene, chloroform, ethyl ether, acetone, ethanol, methanol, and water. ...read more.

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