03 - Chromatography - CHEM 3221 Organic Chemistry I Pre-lab...

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Part A Separating a Mixture of Biphenyl, Benzhydrol, and Benzophenone by Thin-Layer Chromatography Part B Separating Ferrocene and Acetylferrocene by Adsorption thru Column Chromatography , and Gas Chromatography CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY
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Thin-Layer Chromatography
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY ! Chromatography: refers to several related techniques for analyzing, identifying, or separating mixtures of compounds. ! Thin-layer chromatography: simple and relatively inexpensive analytical technique that can quickly and efficiently separate quantities of less than 10 μg of material. ! Applications of TLC: " Rapid analysis of reagent and assesment of product purity " Quickly determine the number of compounds in a mixture " Follow progress of a reaction " Select a suitable solvent before attempting a larger scale column chromatography ! Two-part operation: " The sample mixture is placed into a liquid or gas: mobile phase " The mobile phase carries the sample through a solid support: stationary phase " Compound in the sample mixture move through the stationary phase at different rates, due to different attractions for the mobile and stationary phases Review of Terms
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Choosing Adsorbents and Eluents ! Alumina and silica gel are the most commonly used adsorbents. " Alumina is generally used for chromatography of less polar compounds . (Reversed Phase) " Silica gel is better for compounds containing polar functional groups. (Normal Phase) Note: Water impacts adsorbent activity. For better results, plates are dehydrated by heating in a drying oven and then stored in a dessicator. ! Eluents are organic solvents of various structures and polarities. " The more polar an eluent , the greater is its eluting power, that is, its ability to move compounds over the stationary phase. cyclohexane petroleum ether hexane toluene dichloromethane ethyl acetate ethanol acetone methanol least polar most polar “Different compounds travel at different rates due to the differences in their attraction to the stationary phase, and because of differences in solubility in the solvent.” Thin Layer Chromatography
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY TLC / Column ! What happens? " The stationary phase, called the adsorbent , tends to adsorb the compound from solution. " As the mobile phase, called eluent , travels up (or down for column) the compounds within the mixture move at different rates. ! Why? " Compounds with less attraction for the adsorbent move rapidly with the eluent . " Compounds with more attraction for the adsorbent move slowly with the eluent . ! Adsorbents
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This note was uploaded on 01/23/2011 for the course CHEM 3221 taught by Professor Bean during the Fall '08 term at University of Houston.

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03 - Chromatography - CHEM 3221 Organic Chemistry I Pre-lab...

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