Exp 2: INTRODUCTION TO CHROMATOGRAPHY
Part II: Caffeine in Over-The-Counter Drugs; An Analysis Using Thin-Layer
Chromatography
Caffeine is usually associated with coffee, tea, and cola drinks. Most people
donŐt realize that caffeine is also a part of many of the over-the-counter pain
medications that they take. This part of Exp 2 involves the use of
thin-layer-chromatography on selected over-the-counter medications to
determine whether they contain caffeine or not.
PROCEDURE:
Part A: Extraction of the caffeine
Obtain one tablet (or packet) from the selection of over-the-counter
medications. Grind the tablet to a fine powder using a mortar and pestle.
Transfer the powder to a small centrifuge tube, and add 3 mL of conc
NH3 and 1 mL of chloroform (CHCl3. Mix thoroughly
using a stirring rod and then centrifuge. Draw off the chloroform layer
(the lower layer) using a Pasteur pipet, and transfer the liquid to a small
test tube.
Repeat this procedure with a different pain medication and with a small
portion of pure caffeine. The caffeine will serve as the standard.
Part B: Preparation of the Chromatography Chamber
Add enough of the 1:1 chloroform:acetone solvent mixture to cover the bottom of
the chamber. Cap tightly and leave for at least 10 minutes to allow the
solvent and vapor to equlibrate.
Part C: TLC Analysis
Spot small portions of each sample and the caffeine standard onto the the TLC
plate, putting the caffeine standard in between the two samples. Place the
plate in the chromatography chamber and leave there until the solvent front
has reached to within a couple of centimeters from the top of the plate.
Remove from the chamber and let air-dry or drywith a dryer.
Movie demonstration of a thin-layer chromatographic separation
QuickTime,
MPEG
Place the dried plate in the jar containing the I2crystals, or in
the UV chamber if it is the fluorescent kind. Remove from the chamber (using
tweezers) and immediately circle the spots. If you are using the UV chamber
then circle the spots while still under the lamp.
RESULTS AND DISCUSSION:
Report the presence or absence of caffeine in your samples. Also, (1) compare
your results with those obtained by others in the class and (2) get the results
for the other OTC drugs.
Gwen Sibert
Roanoke Valley Governor's School
gsibert@pen.k12.va.us