Filthy Lucre: A Case Study Involving the Chemical Detection of Cocaine-Contaminated Currency - Case Study Collection - National Center for Case Study Teaching in Science

FILTHY LUCRE
A Case Study Involving the Chemical Detection
of Cocaine-Contaminated Currency

by
Ed Acheson
Department of Chemistry
Millikin University, Decatur, IL

Part II - Lab Work

If you have access to a gas chromatograph/mass spectrometer, you can perform the experiment(s) you designed in Part I.

Pre-Lab Work

Experimental methods exist to screen paper currency for the presence of cocaine (i.e., determine if cocaine is present in money or not). Before you begin any experimental work, however, compile a list of questions, or experimental variables, you should consider in order to help you decide if Mr. Jones does indeed have a case. Try to make the list as complete as possible. You do not have to know the answers to your questions, and some of your questions may not be answerable, but try to ask as many as you can. Here are three example questions to get you started in your thinking:

There are many more questions that we could ask about this problem. Try to generate as long a list as you can to add to these three.

Experimental Work

An instrument called a gas chromatograph/mass spectrometer (GC/MS, for short) is used to detect cocaine. You may not know what a GC/MS is, but you have probably heard of one. When athletes are tested for the use of banned performance-enhancing drugs, a GC/MS is the instrument used to do the tests.

Your instructor will tell you how much you must know about GC/MS. Here is a brief "big picture" overview of GC/MS for those of you who are not at all familiar with the technique. Gas chromatography (the "GC" part) is a powerful technique used to separate the components of a mixture. Mass spectrometry (the "MS" part) is then used to identify the components of the mixture. A urine sample from an athlete, for example, is injected into a GC. The GC then separates all the proteins, metabolites, drugs, etc., present in the urine into individual components. The individual components are then passed into the MS, which identifies what each component is.

In this project, paper currency will be treated with methanol to extract any cocaine present in the money. The extract will then be injected into the GC/MS, which will determine if any cocaine is present in the extract. Your instructor will tell you the maximum number of bills you can test. (The number will depend upon the size of the class, the time and equipment available, how much money you have, etc.) The procedure for extracting a bill is given below:

  1. Roll the bill and place it into a clean vial.
  2. Add 2 mL of methanol to the vial.
  3. Cap the vial and shake for 1 minute.
  4. Using a glass Pasteur pipette, transfer enough methanol to an autosampler vial to fill the vial about three-quarters full.
  5. Remove the bill from the vial when you are finished using a forceps.

Results

After all the bills have been extracted, your instructor will run them on the GC/MS. Your instructor will explain how and where you can get the printout of the analysis of your bill. Be sure your class compiles a table of results for the entire class.

Reflection Questions
  1. Based on the class results, what percentage of paper currency is contaminated with cocaine?

  2. How confident are you that the class results represent all paper currency in circulation? Is there some way you could increase your level of confidence?

  3. How many bills do you think you would have to test to get a representative sample of all bills in circulation? On what basis did you formulate your answer?

  4. Did you observe any patterns to the contamination (for example, based on denomination or geography)?

  5. What might you do in order to get quantitative results (i.e., determine how much cocaine was present in your bill)?

  6. Based on the results of your experiments, if you were the judge in the Jones case, how would you rule? Why? Has you opinion of the case changed now that you have completed your experimental work?

  7. Why is GC/MS the preferred method of choice for determining cocaine?

  8. GC/MS is used for testing athletes for banned performance-enhancing drugs. What are some of the advantages, disadvantages, and limitations to GC/MS for this purpose?


Here's a web site you might find amusing (Accessed Nov. 3, 1999):

"Where Has That Dollar Been?" - Want to know where that dollar in your pocket has been? At Wheresgeorge.com, you can type in the serial number on any bill and track where it has been. It is sort of a hit-or-miss proposition, in the sense that the site relies on a lot of people other than you plugging in the serial numbers of individual bills, but then again a lot of folks seem more than happy to do so. Every couple of tries, you will get a doozy of a circulation history, which makes Wheresgeorge.com a fairly addictive site. http://www.wheresgeorge.com/index.html