Thursday, March 13Th, 2003: You May Come in Anytime Between 9:00 and 2:00PM to Complete

Thursday, March 9th, 2006: You may come in anytime between 9:00 and 3:00PM to complete the experiment.

Questions: see Dr. Seely, NSM C-303, x3778; or Gary Greene, NSM C-323

Thin Layer Chromatography (TLC)

TLC is a very important technique for the rapid separation and qualitative analysis of small amounts of material. TLC is a solid-liquid partitioning technique using a glass plate coated with a thin layer of adsorbent material (silica). The sample is applied to the plate and allowed to move up the plate with the solvent. As the solvent travels up the plate the sample is distributed between the moving liquid phase and the stationary solid phase. A separation results from the differences in the rates at which the individual components of the mixture advance up the plate. Substances that are the most polar travel slowly upward with non-polar substances traveling more rapidly.

You will perform TLC on four known compounds (acetaminophen, aspirin, phenacetin, caffeine) and your unknown.

Be careful when handling the TLC plate not to touch the silica coated surface. Begin by drawing, with pencil ONLY, a very light origin line (be careful not to damage the silica coating or your compounds will not adsorb). After preparing the compounds (see procedure), spot the plate with two of the known compounds and your unknown (see picture below). Do the same on your second plate, spotting it with the other two known compounds and your unknown. You may write lightly with pencil below each spot identifying it as A (acetaminophen), As (aspirin), P (phenacetin), C (caffeine) and U (unknown). Now develop the plates in a bottle containing 100% ethyl acetate (see picture below). Note: make sure the solvent level is BELOW your origin line. You will be able to visibly see the solvent move up the plate. Remove the plate from the chamber when the solvent line is approximately 2 cm from the top of the plate. Now quickly, before the solvent evaporates, draw a line marking the solvent front.

Examine each strip under the ultraviolet light viewer and circle all of the “spots”. Calculate Rf values (see below) for each compound and clearly identify, through comparison of Rf values, your unknown. Note: some compounds, including your unknown, MAY show more than one spot……..

Report DUE: Thursday, March 20th, 1:00PM.