column - Introduction In this experiment spinach extract...

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Introduction In this experiment spinach extract was separated into some of its individual components via column chromatography. A thin-layer chromatography was also performed in order to calculate the R f for each fraction and the original sample. The R f for each fraction were 0.95 for fraction 1, 0.60 for fraction 2, 0.40 for fraction 3, and 0.95 for the original sample of spinach extract. Theory, Reactions, and Mechanisms Chromatography is a method of separating mixtures of substances into their pure components. In the many different kinds of chromatography a mixture of substances is separated into pure components by passing the mixture over an insoluble material to which the substances stick. Substances that stick loosely or not at all move rapidly and those that stick tightly move slowly. The insoluble material over which the mixture passes is called the stationary phase, and serves as an adsorbent. The solvent carrying the solutes over the stationary phase is called the mobile phase. Column chromatography is an isolation and purification technique used extensively by organic chemists to obtain pure samples of chemicals on a large scale. As well as being able to handle large amounts, Column chromatography has the ability to change the eluting solvent throughout the course of the elution. This means one component can be removed while a desired product remains essentially unmoved. A change in solvent will then move the desired product through the column. Solvent changes may include such things as changes in polarity, changes in pH, or changes in ionic strength. Column chromatography ( see figure 1) can be separated into two categories which depend on how the solvent flows down the column. A solvent that is forced down a column
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using air pressure is called flash chromatography. If the solvent is allowed to flow down the column by gravity it is called gravity column chromatography which is what is used in this experiment. Figure 1. Column Chromatography In the stationary phase, two common adsorbents are used, silica gel and alumina. These adsorbents come in different mesh sizes. The larger the mesh size the smaller the adsorbent particles. The size of the adsorbent particles affects how the solvent moves through the column. A larger particle is used for gravity chromatography. Alumina is a more commonly used absorbent for column chromatography. Alumina, which can be acidic, neutral, or basic, is water sensitive meaning the higher the water content, the less polar site it has to bind organic compounds.
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This note was uploaded on 01/08/2009 for the course CHEM 0320 taught by Professor Kazunorikoide during the Spring '08 term at Pittsburgh.

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column - Introduction In this experiment spinach extract...

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