TLC Lecture Handout - Extrac'on Ques'on When doing an...

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Unformatted text preview: Extrac'on Ques'on When doing an extrac'on an emulsion layer may form. Adding a solu'on of saturated NaCl to the mix will o=en break up the emulsion. This is due to: A. The NaCl making the aqueous solu'on more ionic disfavoring miscibility of the solvents B. The NaCl reac'ng with the compound to pull the compound into the organic layer C. The NaCl makes the solu'on basic to separate the two layers. D. The NaCl is an inorganic salt and therefore has no affect on the organic solvents separa'on with the water. Extrac'on Calcula'on Example Thin-Layer Chromatography (TLC) Iden'fica'on Technique U'lizes differences in ______ of compounds TLC can be used to: Determine the number of compounds in a mixture Establish whether two compounds are iden'cal** Monitor the progress of a reac'on TLC Overview A small amount of sample is spoTed on the TLC plate The TLC plate is placed in the chamber ( jar with solvent) and "developed" Developed = solvent allowed to rise up the TLC plate by capillary ac'on The TLC plate is removed from the chamber & the solvent edge is marked Visualiza'on techniques (UV light, stains) are used to see the "spots" corresponding to compounds A picture version. . . Adsorp'on Chromatography: How TLC Works Sta'onary Phase: _______________ Mobile Phase: ___________________ _______________ solvent Comp. A Comp. B adsorbent Adsorp'on Chromatography Con'nued As solvent moves along sta'onary phase, compounds are moved. Movement depends on ________! __________ compound s'cks more to polar sta'onary phase! solvent Comp. A Comp. B Determining Rf Rf = _______________ Solvent front 55 mm 40 mm 26 mm Spot B Spot A Before development After development A: Rf = 0.47, B: Rf = 0.73 Effect of Solvent Choice Polarity of solvent also affects movement on TLC plate! mixture of nonpolar compounds mixture of polar compounds mixture of polar & nonpolar compounds Iden'cal Rf = Iden'cal Compounds? Does finding iden'cal Rfs for two samples necessarily mean that they are the same compound? TLC Ques'on Which of the following is NOT a possible source of error in developing TLC plates? A. The solvent level in the developing jar was too high B. Not enough sample was spoTed C. Too large of a sample diameter was spoTed on the plate D. Using iodine staining to visualize spots E. Breaks in the TLC sta'onary phase Experiment 4 Plan A. Analgesics Standard Samples B. Analgesics Unknown Need to extract ac've ingredients from tablet or powder C. TLC of Crude Caffeine Make sample in a small test tube OR directly in the vial Iden'fy caffeine spot, report any others VERY IMPORTANT!!! DO NOT CONTAMINATE: Developing solvents (no double-dipping pipeTes!!!) Standard samples Your unknowns! Rinse spoTers with acetone Clean out and dry your jar when changing solvent systems! Calculate Rf for all compounds Draw TLC plates in your notebook ...
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