Isolation of Caffeine from Coffee Using Solid Phase Extraction with C-18 Silica

Procedure:

1. Prepare an SPE tube loaded with 500 mg of C-18 (octadecylsilane) bonded silica gel.
2. Apply 5-10 mL of brewed or instant coffee to the column and draw through using a vacuum.
3. Draw air through the column for 3-5 minutes or until dry.
4. Elute the column with 10 mL of ethyl acetate.
5. Evaporate the eluate and obtain an IR spectrum of the product for structure confirmation, or inject into GC or HPLC for analysis.

Notes:

1. Commercial 6 mL-500 mg BAKERBOND SPE columns may be used. However, it is more economical to prepare the columns from bulk C-18 silica.
2. 10 mL extracted about 95% of the caffeine. A second 10 mL extraction gave essentially quantitative recovery.
3. A good IR can be obtained from 1 mg of caffeine as a KBR pellet. A capillary GC method has been reported which would be good for GC-MS analysis. HPLC analysis can be performed with a mobile phase of 40% water - 60% methanol plus about 1% acetic acid using a C-18 column.

Discussion: This experiment is a good alternative to the traditional separatory funnel method using a strong tea bag concentrate, particularly if methylene chloride is being used for extraction. Methylene chloride is now considered a carcinogen. An 8-oz. (about 250 mL) cup of moderately strong coffee contains from 80-200 mg of caffeine, depending on the type and brewing method. This experiment was developed using a "standard" cup of "coffee" containing 100 mg of caffeine in 250 mL of water. Students can compare different coffee brews for caffeine content.

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© February 1996.

DISCLAIMER:

These experiments are designed to be used in college and university level chemistry laboratory courses, and assume the availability of routine supplies, equipment, and instrumentation usually associated with organic chemistry laboratory courses, as well as an appropriate modern level of supervision, safety training, personal protective equipment, and other safety facilities. Any users of these procedures assume all responsibility for the safe handling of hazardous chemicals and procedures. In any event the authors, webmasters, The University of Wyoming , Rochester Institute of Technology, or Dartmouth College shall not be liable for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these procedures.