Thin Layer Chromatography
Submitted in partial fulfillment of the requirements for:
Organic Chemistry Laboratory
Dr. Robert Duncan
Fall Semester 2012
Caitlin Inman, Team Leader
October 9, 2012
Tyler Byrd, Data Collection
Shared Role, Technique Expert
“Chromatography is used to separate components of a mixture. For example, imagine a mixture of wood pieces, pebbles, and large rocks to be separated and the chromatography setup as a stream. Flowing water is then the moving phase, and the bottom of the stream is the stationary phase. If our mixture is thrown into the stream, the wood pieces will move freely with the flowing water. The wood has, therefore, a high affinity (or attraction) for the moving phase. The large rocks will stay at the bottom and, thus, have a high affinity for the stationary phase. Finally, the pebbles will roll slowly at the bottom and have an intermediate affinity for the moving phase and for the stationary phase” (Brozek). Thin Layer Chromatography (TLC) is a solid-liquid technique in which the two different phases are a solid stationary phase and a liquid mobile phase. TLC can be used to detect a given compound in a mixture, follow the course of the reaction, follow the purification of a compound, or evaluate the purity of the compound.
Certain objectives needed to be met in order for the Thin Layer Chromatography (TLC) experiment to be understood and completed. The identification of an unknown, and the techniques and principles of TLC had to be mastered to identify an unknown substance based on comparisons of lab standards and Rf factors. The next objective was to measure the distance a solvent travels and how to calculate the Rf factor of a compound.
Table of Physical Constants:
| Molecular Weight(g/mol)
| Boiling Point °C
| Melting Point°C
| * Toxic * Dangerous for environment
| * Harmful
| * Dangerous for environment
| * Harmful
| 5,5-dimethyl-1,3-cyclohexanedione C8H12O2
| * Sensitive to skin * Irritant * Non-hazardous
| Petroleum Ether
| * Highly flammable * Toxic
| Ethyl EtherC4H10O
| * Harmful * Highly flammable * Toxic
To begin, an unknown was obtained and a number recorded. Tests were then prepared so that they could be run on the unknown. First, 12 open ended capillary tubes were extruding using a Bunsen burner to use for spotting samples onto the TLC paper. To extrude the tube, the capillary tube was heated at its midpoint with a Bunsen burner and rotated till soft. When it became soft, the heated portion was drawn out approximately 5 centimeters, and allowed to cool then broken in half. Next, an approximately 67 mm tall TLC flexible plate was cut so it could be placed inside a 600 mL beaker. Then, a 600 mL beaker was setup as a developing chamber by cutting a piece of filter paper that extended from the bottom of the beaker to almost the top, against the wall of the beaker. The filter paper was then placed inside the beaker and moistened with Petroleum Ether, and covered with a watch glass so the solvent did not evaporate. Next a line was drawn on the TLC plate approximately 1 centimeter from the bottom of the plate, and on that line six evenly spaced lines were labeled in the following order: 1st unknown, p-nitrotoluene, acetanilide, biphenyl, p-dimethylaminobenzaldehyde, and 5,5-dimethyl-1,3-cyclohexanedione. Then, using the extruded capillary tubes, a spot was placed on the TLC paper with the prepared solutions. Each spot was spotted twice, and allowed to dry in between each spotting. Next the...
Cited: 1. Brozek, Celestyn M., Chromatography, Journal of Chemical Education 1999 76(1), 83, ACS Publications http://pubs.acs.org/doi/pdf/10.1021/ed076p83.
2. Malins, Donald C. and Wekell, John C., TLC-Versatile Tool. Journal of Chemical Education 1963, 40 (10), 531, ACS Publications http://pubs.acs.org/doi/pdf/10.1021/ed040p531.
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