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04Post - OBJECTIVES Learning Separation and Identification...

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9/23/2011 1 Separation and Identification of Food Dyes by A TEST EXERCISE - 105 points) 1 Last Update: 9/23/2011 8:11 AM What is the quantitative basis for chromatographic separation What experimental conditions optimize chromatographic separation? What properties can be the basis for separation of mixtures ? OBJECTIVES With what accuracy can you identify the food dyes in an unknown mixture by paper chromatography? Learning: Performance/Assessment: 2 Concepts: capillary action chromatography components interactions mobile phase migration rate mixture origin rates resolution retention factor solvent front solvents spot stationary phase 3 Techniques: preparing chromatogram optimizing resolution measuring spots Apparatus: solvent chamber (beaker/watch glass) ruler chromatogram 4 In paper chromatography of dyes, primary basis for separation is interaction between dye molecules and paper . Paper consists primarily of CELLULOSE , a high molecular weight polymer of the carbohydrate GLUCOSE (C 6 H 10 O 5 ) n O O O HO H O C H 2 OH O O HO C H 2 HO OH ..... Three water-like hydroxyl units can HYDROGEN BOND to water or to IONIC dye molecules 5 6 For a given solvent, dyes that bind to paper more tightly move more slowly I.e., have lower migration rates Origin Liquid Level Solvent Front 6 Migration Rates - Qualitative
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9/23/2011 2 Migration Rates - Quantitative Distance moved by COMPONENT R f = −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Distance SOLVENT FRONT has moved For a given: The RELATIVE MIGRATION RATE and therefore, R f for a given substance with a given stationary phase and given solvent is REPRODUCIBLE Solvent Front Origin d solvent d spot
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