Summary of Procedure:
Thin Layer Chromatography is the first experiment of the 1st semester introductory sequence.
The students perform a series of TLC experiments on 6 known compounds.
They observe the effects of three solvents (hexane, dichloromethane, & ethyl acetate) on the Rf values of the compounds.
Students work in groups to combine their data.
They then each receive a mixture of unknowns that is analyzed with TLC.
Positive aspects of this experiment:
+The beauty of TLC is that a complete experiment can be done in a matter of 15 minutes. This allows for them to “learn as they go” and experiment with different techniques.
+ In our labs we do many TLCs over the course of the year, so this is a good place to start.
+ TLC gives some clue as to the polarity and function groups of the unknowns, but much more information is necessary to make a definitive identification.
Neutral (may be positive or negative) aspects of this experiment:
± The theory of TLC is rather involved. Some aspects of solvent polarity are explained but the theory is not described in detail.
Negative aspects of this experiment:
- TLC Rf values are notoriously unreproducable, especially for novices. At the best, general trends can be observed.
- “Learn as you go” can use up a lot of relatively expensive TLC plates.
Inquiry & Extension Ideas:
● Students can experiment with various pure solvents and solvent mixtures to target separations and Rf values.
● This is a good experiment to use “class data” as part of the discussion.
● The previous years’ results can be used to prepare for the experiment as well as to analyze and discuss data.
A good article to consult is "Thin-Layer Chromatography: The 'Eyes' of the Organic Chemist" Dickson, Kittredge, & Sarquis J. Chem. Ed. (81) 2004 p. 1023
Data Links:
Student Comments:
Photo Gallery:
01_Schretzman_TLC
Student Handout 2008 version
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