Attempts to Detect Cocaine on Money: A Great Exploration for National Chemistry Week 2016

Detecting cocaine on money

The theme for National Chemistry Week (NCW) for 2016 is “Solving Mysteries through Chemistry: Exploring the Chemistry of Fibers and Forensics”. To prepare for NCW, I’ve been trying to learn as much as I can about forensic science and chemistry. One of the more interesting topics I’ve learned about is how cocaine (C17H21NO4) adheres to and can be detected on paper currency. I thought I would take on the challenge of trying to figure out a way – using materials commonly found in high school chemistry laboratories – to detect this illegal drug on $5 bills. Turns out this challenge was a bit tougher than I initially imagined it might be!

Cocaine is an illicit drug that is generally bought and sold using cash. Because both sellers and users handle the drug and money, cocaine can become adhered to fibers in paper currency during purchasing transactions.1-4 Furthermore, people sometimes use banknotes to inhale the drug. The cocaine adhered to bills is transferred during note to note contact, such as in cash registers and bank counting machines.1 Several analytical techniques (gas and liquid chromatography, mass spectrometry, capillary electrophoresis and more)1-3 have been used to investigate the amount of cocaine present on paper currency. The amount of cocaine on any single bill varies widely based on location, age, and other factors. Of note, 1.3 milligrams of cocaine was found on a single $1 bill in Ohio!1,2 In general, 90% or more of banknotes across the globe contain traces of cocaine.1-3 While amounts vary widely, U.S. bills of varying currency can be expected to have roughly 3 to 30 micrograms of cocaine.2-3

Cobalt (II) thiocyanate, Co(SCN)2, can be used to test for the presence of cocaine in protonated form (C17H22NO4+), due to its reaction with cobalt thiocyanate to form a blue product:5-6

[Co(SCN)(H2O)5]+(red, aq) + 3 SCN-(aq) + 2 C17H22NO4+(aq) –> [(C17H22NO4)2Co(SCN)4](blue, aq) + 5 H2O(l)

In the Illustrated Guide to Home Forensic Science Experiments4 by Robert and Barbara Thompson (a FANTASTIC resource for NCW 2016, by the way), it is stated that a 0.11M solution of Co(SCN)2 can be used to detect cocaine in the amount of 60 micrograms or more. (if you don’t have Co(SCN)2 on hand, a solution of a mixture of 0.11 M CoCl2 and 0.11M KSCN is reported to work equally well).4 Because most bills contain much less than this amount, the probability of using this test to detect cocaine on a single banknote is low. According to Thompson and Thompson, your chances of achieving a positive test increase if you live in an urban area where cocaine use is prevalent.4 However, not all studies agree with this claim.1

I set out to see if I could collect enough cocaine from U.S. $5 bills for a positive test using Co(SCN)2. To do so, I used methanol as the solvent to transfer cocaine from banknotes to a Q-tip. I used methanol rather than water as the solvent because methanol dissolves both the acidic and basic forms of cocaine, whereas water only dissolves the acidic form.7

To conduct tests, I placed 2 – 3 drops of methanol on a Q-tip, and then ran the moistened portion of the Q-tip along the entire front surface of a $5 bill. I then placed 2 – 3 fresh drops of methanol on the Q-tip and repeated the process on the opposite side of the $5 bill. Using the same Q-tip, I repeated this process again for a total of five different $5 bills. Each time, I tried to rub the very same portion of the Q-tip over the surface of each side of all five $5 bills. This was done to so as to concentrate material on to the same area of the Q-tip to increase the probability of a positive test. After concentrating material on the Q-tip, I added 2 – 3 drops of 0.11M Co(SCN)2 to the appropriate area of the Q-tip. Finally, I added 2 – 3 drops of 12M HCl to convert any basic form of cocaine on the Q-tip to the acidic form (recall it is the acidic form that reacts with cobalt (II) thiocyanate to form the blue complex). You can see this procedure carried out in the video below:

You will note that the positive results achieved were subtle. In fact, some might argue that I didn’t actually achieve a positive test. Nevertheless, I could see shifts to blue color several (but not all) trials. In a total of 19 trials, 7 resulted in a positive test, 11 were negative, and one test was deemed to be inconclusive (an extremely faint color change to blue was observed).

If you think this experiment looks a bit time consuming, you’re right. If you’d rather not go through the hassle of trying to extract cocaine from currency, diphenhydramine (C17H22NO+ in acid form) tablets can be used to spike banknotes to easily illustrate how this test works. Similar to cocaine, diphenhydramine (the active ingredient in Benadryl) reacts with cobalt thiocyanate to form a blue product. A likely reaction for this process is:

[Co(SCN)(H2O)5]+(red, aq) + 3 SCN-(aq) + 2 C17H22NO+(aq) –> [(C17H22NO)2Co(SCN)4](blue, aq) + 5 H2O(l)

Spiking bills with diphenhydramine adds the benefit that you can pretty much guarantee strikingly positive test results. In the video below you can see how to carry out the cobalt (II) thiocyanate test with diphenhydramine. Because it is much easier to achieve and identify a positive test with diphenhydramine, it’s a good idea to try this experiment to see how a strongly positive test might look when testing for cocaine on bills.

If you try out this experiment on your own, I’d love to hear from you. I’d also like to hear any comments about this experiment. Perhaps you think the results I achieved are too subtle to indicate the presence of cocaine on $5 bills. Let me know if you think this is the case. Also, let me know if you have any suggestions on how to improve chances of detecting cocaine using this (or any other) method. Remember, however, I’m looking for tests that can be conducted using materials found in high school labs! Given that I live in (and collected all $5 bills tested from) a rural town of about 7500 people, I’m interested to see if stronger and positive results occur more often using banknotes obtained from large cities. I’m also interested to see if $1, $10, $20, or bills from other countries provide a greater chance of achieving positive results. Finally, let me know if you might you use this experiment during NCW, if you successfully used this method to detect cocaine on any currency, or if you were able to achieve a higher probability of positive results than I. Please share your thoughts, suggestions for improvements, and results of experiments in the comments below. I look forward to hearing from you and your students!









Join the conversation.

Comments 6

Eric Sullenberger | Sun, 09/11/2016 - 22:32

I used the CoCl2 and K(SCN) method because that is what I had available on my shelves.  I tried to detect cocaine on my money, but didn't go over the threshold, so I don't know if it was successful.  I then brought in a benadryll pill the next day, crushed it, and coated a bill in it, but then still got a negative test.  However, I got a positive result when I dripped a drop of the test solution into the mortar I used to crush the pill so it must be my swabbing technique that is off or I was too impatient waiting for a color change on the swab.  I managed to get some bills in a big city near me and so I'm going to play with it some more this coming week and will try to post another reply if I get success.

Tom Kuntzleman's picture
Tom Kuntzleman | Mon, 09/12/2016 - 08:21

Mr. Sully:

Thank you for trying this and letting me know about your results! 

If you are not getting a positive test using the benadryl, then I would suspect you could improve your extraction technique. You are using water to extract benadryl and methanol to extract cocaine, correct? I found better results using water for benadryl extraction (would sometimes get negative results using methanol). I would get better results using methanol for cocaine extraction.

FYI, I spent about 30 seconds rubbing each bill with a Q-tip. Push down firmly when rubbing the bill; you will often see the tip darken due to some "dirt" or ink transfer onto the Q-tip. The Q-tip should be moist, but not dry. You don't want it so wet that the bill becomes noticeably wet. This will favor the transfer of material from the Q-tip to the bill. A moist tip favors transfer from the bill to the tip. Material will dissolve wherever it finds appropriate solvent. Thus, wet tip and dry bill as much as you are able.

I was concerned about using CoCl2 and KSCN because a 0.11M Co (II) solution made this way will have a higher ionic strength, disfavoring the formation of the blue complex. Thus, I did not try this recipe. Co(SCN)2 is not too expensive; you can get 5 grams for around $50 here.

I look forward to hearing about your future explorations!


Erich Blossey | Mon, 10/10/2016 - 11:51

Detection of cocaine in currency: The chemists at JEOL demonstrated their then new mass spectrometer, DART (direct analysis in real time- initially called fast analysis in real time [*ART] in Japan but dropped that name in their American subsidiary) ability to detect cocaine on the bills, from $1 to $20s, obtained from workshop participants ! What makes the demo impressive is that the DART has an atmospheric pressure interface so all one does is wave the bill or any object in front of the interface and it is “ingested” into the inlet chamber of the MS. Cocaine is easy to detect by MS from its unique fragmentation pattern. 

Tom Kuntzleman's picture
Tom Kuntzleman | Tue, 10/11/2016 - 07:09

Erich:  Thank you for alerting me to the DART experiment. What an amazing demonstration; I would love to actually be able to see this performed first hand. The anocrym story is hilarious. Thanks for your input! 

Grazyna Zreda | Fri, 11/04/2016 - 15:20

My students tried this technique during the NCW.  We have used CoCl2 and KSCN to prepare the solution, and tried it first with the Benadryl - spiked dollar bill.  It worked great, even with just one pill crushed in the mortar.  Then we tested several $1.00 bills, $20.00 and one $50.00 bill.  Interestingly, the dollar bills yielded positive result with just 4 bills.  With the twenties, one set of 4 bills was strongly positive, the other was inconclusive.  The $50.00 bill was also inconclusive (color developed afer a while but it was very faint).  To make the technique safer for students, I used 6 M HCl rather than concentrated HCl, but otherwise we stayed true to the procedure.  The bills were quite new, so the positive test was quite a surprise to us.

It would be interesting to see if other chemicals would give a false positive but we did not have time to test that yet.  Thank you for referencing the forensic book and the link, it was a new resource to me.

Grazyna Zreda

TVHS, Tucson AZ

Tom Kuntzleman's picture
Tom Kuntzleman | Sat, 11/05/2016 - 09:15

Grazyna, thank you so much for reporting the results of your students and your investigations! I appreciate knowing that KSCN and CoCl2 worked. Using of 6 M HCl is also an extremely useful modification, so thank you for alerting me to this. It sounds like you got very good results - much better than I. I wonder if this is a result of you living in a more urban environment than I. I wish I could see with my own eyes the results that you report here and in Chemical Mystery #8! Tell your students I said nice job.