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lab 2 - Separation of Dyes Inks and 1,2-Cyclohexanediol...

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Separation of Dyes, Inks and 1,2-Cyclohexanediol Diastereomers by Column and Thin Layer Chromatography Mayank Kumar February 16, 2007 Methods and Background The purpose of the experiment was to devise a column chromatography system that completely and efficiently separates methyl orange and methylene blue, to create a thin layer chromatography system that separates the different dyes in black, blue, green and red Vis-à-vis pens, and to develop a thin layer chromatography system that separates the two diastereomers of 1,2-cyclohexanediol, cis -1,2-cyclohexanediol and trans -1,2-cyclohexanediol. N Me Me N N S O OH O S N N N Me Me Me Me Methyl Orange Methylene Blue OH OH OH OH cis -1,2-cyclohexanediol trans -1,2-cyclohexanediol The experiment used thin layer and column chromatography as analytical techniques. In both types of chromatography, a liquid mobile phase flows over a solid stationary phase, and the mixtures’ components separate unequally due to differing affinities (based on intermolecular interactions) for the two phases. Specifically, the components establish a dynamic equilibrium with the two phases, and the components that are most attracted to the stationary phase adsorb to it more often and for longer periods of time, thus slowing their movement because they have to be in the mobile phase to move. In the experiment, the stationary phase was composed of silica gel, a polar compound, so the components of the mixture adsorbed to the stationary phase on the basis of polarity (dipole-dipole interactions); that is, the more polar compounds were slower to move and separate. Although there was some competition for the polar components between the stationary phase and the mobile phase (which increased as the polarity of the mobile phase increased), the stationary phase was more polar so the components were more attracted to it.
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Retention factor (R f ) values, which are calculated by dividing the distance a component travels by the distance the mobile phase travels, increase as the mobile phase becomes more polar, causing the components to move farther. Similarly, if the stationary phase is overwhelmingly polar in comparison to the mobile phase, the R f values will decrease. Retention times, however, have inverse relationships with R f values; thus, as the mobile phase becomes more polar, retention times will decrease, and if the stationary phase is much more polar than the mobile phase, retention times will increase. In thin layer chromatography (TLC), an adsorbent is used as the stationary phase and a drop of the sample solution is placed on it. The adsorbent is then placed in a small amount of the mobile phase, and as the mobile phase moves up the adsorbent, the separation of the components takes place. In column chromatography, a specialized column is set up in which the sample solution is added to a solid adsorbent (stationary phase), and the mobile phase is passed through the column, resulting in separation of the components of the sample.
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