CHEM253
Caffeine from Tea, Part II
Experiment 8
1
A new consumer group, Consumers for the Education of Caffeine Abusers (CECA), has
been formed to educate the general public on the ubiquitous presence of caffeine in the
American diet. Currently, consumer foods are not required to publish on the label the
amount of caffeine their product contains. Consumers must rely on internet sites such as
http://wilstar.com/caffeine.htm that publish the caffeine content of various beverages to
determine the amount of caffeine they are ingesting. Typically, the simply publish
caffeine content data that has been supplied by manufactures. This data may be
deliberately falsified to protect their brand or unintentionally misinterpreted due to poor
experimental design.
CECA has heard about our recently acquired expertise on the extraction of caffeine from
tea and they are soliciting the help of Dominican University’s organic chemistry class to
help them develop methods to measure the quantity of caffeine in various consumer
products. Your task in this lab period will be to design and perform an experimental
procedure to isolate caffeine from the beverage of your choice.
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Prelab:
1) Choose a caffeine source.
2) Research the amount of caffeine you would expect to isolate from this source. Try a
website such as http://www.energyfiend.com/the-caffeine-database/
3) Design an experimental protocol, based on your experience with the “caffeine from
tea” laboratory experiment. You do not need to hand this in.
In lab:
1) Save a small sample of your original caffeine source for analysis.
2) Observations: Write down a detailed experimental method in your lab notebook of
what you did in lab. For example, describe what you did in a way that someone who had
not already done Part I could understand. Include the glassware (200mL beaker, 250mL
separatory funnel, etc…) you used, grams of solid chemicals, and volumes of liquid
chemicals.
3) Do not sublime your extracted caffeine.
4) Obtain the mass of your extracted (crude) caffeine before you subject it to
chromatography and spectroscopy.
Depending on the amount of caffeine extracted and the availability of the instruments you
will perform several experiments to determine the identity and purity of your extracted
caffeine.
CHEM253
Caffeine from Tea, Part II
Experiment 8
2
You will subject your “caffeine from tea” sample and your new caffeine sample to
various analytical tests in order to ascertain the identity and purity of your samples.
TLC:
Test your caffeine from this lab side-by-side with your “caffeine from tea” sample and a
sample of pure caffeine on a TLC plate. Record the results (including Rf values) in your
lab notebook.
impurity 2
impurity 1
caffeine
void volume
Absorption at 254 nm
HPLC (High Pressure Liquid Chromatography):
This method gives much the same information as TLC. The caffeine sample is dissolved
in a solvent and introduced into a column that separates the compounds in a mixture in
much the same fashion as TLC. The eluant of the column is monitored with UV
absorption. Compounds show up as “peaks” on the chromatogram.
time of chromatography experiment
CHEM253
Caffeine from Tea, Part II
Experiment 8
UV spectrum:
Obtain an ultraviolet (UV) spectrum of your caffeine sample.
You will need to dissolve your sample in methanol to do this.
Determine the wavelength of maximum absorption (in nm).
Compare your UV spectrum to the spectrum of pure caffeine.
http://chrom.tutms.tut.ac.jp/JINNO/DRUGSPECTRA/sp02caffeine.gif
IR spectrum:
Obtain an InfraRed (IR) spectrum of your caffeine sample.
You will need to dissolve your sample in water to do this.
Compare your IR spectrum to the spectrum of pure caffeine.
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_index.cgi?lang=eng
3
CHEM253
Caffeine from Tea, Part II
Experiment 8
4
Lab Report:
1) A copy of your experimental protocol and observations will be included in your
laboratory report that is due a week after the experiment has been completed.
2) Compare your actual recovery of crude caffeine with your predicted amount. Why are
they different?
3) Include all chromatographic and spectroscopic images.
4) Interpret the results of your chromatograms and spectra. In other words, describe what
these analyses show you about your sample. For example: Did you isolate caffeine? How
pure is your isolated caffeine?