Chemistry Reference
In-Depth Information
3. For the unknown samples, measure the distance that each
component traveled (from the origin to the center of the spot).
Record these measurements on the data table.
4. Calculate the Rf
f
value for each of the solutions and the components
using the data recorded on the data table.
R
f
=
distance solution traveled
distance solvent traveled
5. Compare the R
f
values for the two unknown solutions with those for
the four known TLC plates. Which components do you think each of
your unknown samples contains?
6. Did any spots appear on the unknown sample plates that did not
match a known solution? What do you think those components
might be?
7. Why was it important to draw your origin line in pencil and not pen?
8. How might your results be different if you used too much of each
solution? If you did not use enough?
What's Going On?
Thin layer chromatography requires a solvent that will attract the solutions
on the baseline strongly enough to move them up the plate, but not so
much that they form strong bonds with the compound. As the solvent
rises, the force of gravity pulls the compound and solvent apart. The
solvent used in this lab was a 95:5 mixture of ethyl acetate and acetic
acid. Because it has slightly
polar
and nonpolar characteristics, it can
attract the components in the analgesics long enough to move them
away from the baseline, but not all the way to the solvent front. The
components of the known solutions behave the same way as those
identical components present in the analgesic tablets because they have
the same chemical structure. The porous silica coating on the TLC plate
locks each compound in place until it can be viewed. Compounds on a
silica plate are often difficult to see without the use of a UV light or a
stain such as iodine.
Connections
Thin layer chromatography is just one type of chromatography that is used
to separate compounds. Paper chromatography can separate dyes and
colored compounds from solutions. This type of chromatography uses a
porous type of paper, such as filter paper, and a nonpolar or slightly polar
