Extraction Method

Extraction:

Take a 150 mL Erlenmeyer flask, and add to it 8 g of coffee grounds.  Add to it 50 mL of methylene chloride.  Allow the coffee to extract for 5 minutes. Remove the bulk coffee grounds from the solution.  If coffee is allowed to remain longer, caffeine may become overrepresented in the sample.  Some methylene chloride will be retained by the coffee – this is an acceptable loss, and no dilution is necessary.

Preparation:

Separate the coffee extract from above into three equal portions; assuming some loss of methylene chloride, as above, these portions will be about 15 mL each.  These will become the ‘high’, ‘medium’, and ‘low’ concentrations.  One portion can be set aside and sealed – this will be the ‘medium’ concentration sample source.  The other two portions will be made into the ‘high and ‘low’ solutions. 

The ‘high’ sample is prepared by leaving uncovered to allow the methylene chloride to evaporate until about 1 mL remains.

The ‘low’ sample is prepared by a 10x dilution.

Due to the volatility of methylene chloride, all samples should be stored in airtight containers well below room temperature.  Store in the refrigerator, or if space permits, the freezer.

Standards:

Standard solutions of caffeine in methylene chloride should be made to these concentrations:  500, 100, and 20 ng/uL.  Shown in other units, this is: