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Experiment 2 - EXPERIMENT 2 Paper Chromatography EXPERIMENT...

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E XPERIMENT 2 Paper Chromatography 11 E XPERIMENT 2 Paper Chromatography 2.1 Purpose In experiment 2, plant pigments dissolved in an organic solvent extract will be separated using chromatographic techniques. 2.2 Background In 1906 the Russian botanist Alexander Tsvett extracted the plant pigments that produce the fall colors in leaves by grinding them up in a solvent. If he poured the solvent extract containing the mixture of dissolved pigments through a tube full of powdered chalk, that is CaCO 3 or calcium carbonate, the various pigments separated into colored bands as the extract flowed down through the powdered chalk by gravity flow. He carefully removed the column of chalk from the tube and separated the colored bands. The different colored bands were subjected to extraction with additional solvent. This way, solutions of the separated pigments were obtained. Tsvett termed this new technique chromatography , which literally means “color writing”. Since its discovery chromatography has become a vital tool for separating organic and inorganic compounds, and is used as analytical method as well as on a preparative scale. In all forms of chromatograph y there is a mobile phase and a stationary phase , and chromatography is based on the partition equilibrium for a given solute between the two phases. The mobile phase moves through the stationary phase from one end to the other carrying the substance of interest with it. A solute –a compound that is dissolved in a solvent- with a greater affinity for the mobile phase will spend more time in this phase than a solute that prefers the stationary phase. As a result of this, as different solutes move through the stationary phase they separate from one-another. The stationary phase for most chromatographic separations is usually a solid, and this method is referred to as adsorption chromatography. The mobile phase can either be a liquid or a gas, and the corresponding chromatographic techniques are termed liquid chromatography and gas chromatography , respectively. A technique, in which a liquid serves both as stationary phase as well as mobile phase, is referred to as liquid-liquid partition chromatography.
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E XPERIMENT 2 Paper Chromatography 12 In this experiment, a form of adsorption chromatography known as paper chromatography will be used to extract colored components from a plant extract. Paper chromatography is a useful technique for separating and identifying pigments and other molecules from cell extracts that contain a complex mixture of molecules. The stationary phase in paper chromatography is a strip of paper, which then is placed in a solvent. Only one end of the paper strip is in contact with the solvent reservoir. The solvent moves up the paper by capillary action, which occurs as a result of the attraction of solvent molecules to the paper and the attraction of the solvent molecules to one another. As the solvent moves up the paper, it carries along any substances dissolved in it. The solutes are carried along at different
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