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Forensic Chemistry course lets students experience hands-on CSI

April 5, 2012
By cnp
Posted in Chemistry

Ben Martin and Denise Wirth waited patiently as the minutes ticked off the clock.?Three test tubes, labeled "A," "B," and "C" sat on the counter, each holding an unknown substance immersed in a carefully prepared solution of vanillin, acetaldehyde, ethyl alcohol, and hydrochloric acid.?"My money's on 'A,'" Martin said as their 10-minute wait came to an end.

Wirth handed Martin a small beaker of chloroform, and the only sound was the clink of glass as Martin poured the chloroform into the test tube labeled "A." Everyone leaned in to take a look. Martin held the test tube up to the light. "Oh, that one’s definitely got some purple on it! Wow!" Dr. Doria exclaimed. "Yeah, you didn’t even need the chloroform. Which one was that?" "A," Martin and Wirth said together. "I knew I was right!" Martin exclaimed.

While Martin had correctly guessed which sample would cause the solution to turn purple, a guess can’t be used as evidence in a court of law. It was the chemical test - a simple presumptive test known as the Duquenois-Levine Test - which established that the sample labeled "A" most likely contained Tetrahydrocannabinol (THC), the primary psychoactive chemical found in marijuana. And in fact, the sample was marijuana, provided by (and carefully watched over by) an officer from the Clarksville Police Department. What were the other two samples? Ordinary pipe tobacco and oregano.

Ben Martin and Denise Wirth prepare a sample for analysis using the Duquenois-Levine Test." src='data:image/svg+xml,%3Csvg%20xmlns=%22' data-src=

Ben Martin and Denise Wirth prepare a sample for analysis using the Duquenois-Levine Test. The test is a presumptive test used to indicate the presence of Tetrahydrocannabinol, or THC, the primary psychoactive chemical in marijuana.

The Duquenois-Levine Test is just one of several specialized tests Martin, a senior chemistry major from Hot Springs, Ark., and Wirth, a senior chemistry major from Bella Vista, Ark., have learned this semester as part of Dr. Bill Doria’s Forensic Chemistry class.

The use of forensic tests in a criminal trial might be traced back to 1752, when the results of a primitive chemical test helped convict Mary Blandy of using arsenic to poison her father. As knowledge and understanding of chemistry grew, forensics came to play a more and more important role in the courtroom. However, while most people probably knew that forensic chemistry was an important tool in the legal process, it may have been the debut of the television show CSI: Crime Scene Investigation that brought the word "forensics" into the American vernacular. While the show is criticized by some as being a less than accurate portrayal of the role of the criminal investigator, Doria said the chemistry he saw depicted on the program sparked an idea.

"About five or six years ago I was thinking about upper level [chemistry] courses that students would be interested in taking," Doria said. "My passion, my specialty, is things that are a little bit more technical, so I was looking for something that’s a little bit more user friendly that I could also teach. Of course CSI and TV shows like that were, back then, real popular so I figured [the forensic chemistry course] was something that maybe would catch some people’s eye." Doria was right - the course has become one of the more popular upper level chemistry courses that he teaches.

The format of the class is straightforward: first, teach the students the theory behind the most common forensic techniques. "Lecture is more the usual standard stuff," Doria said. "We talk about the statistics angle, and we talk about lab. We talk about the synthesis of different drugs. That’s important to know, not just because you’ve got to know your enemy, it’s also important because different ways of producing the drug are going to leave different traces of the starting materials."

Then, as with most chemistry courses, after the lecture there is a lab. But these are not your ordinary chemistry lab session. Doria adds an interesting twist….

"Dr. Doria always does a good job of making the labs fun with his little ‘back-stories,’" Martin said. "He gives you a [real-life scenario for each lab]." Holding up the instruction sheet from the last lab, Martin said "This one was pretty funny." In the scenario, the target of the investigation is a Senator suspected of possessing marijuana. Wirth and Martin were asked to analyzing six suspicious substances "taken" from the imaginary Senator’s office to determine if any of them might be marijuana. "We had to figure out if it was the coffee giving him a false positive, and run tests on the tobacco on his desk," Martin explained. "The back-stories are teaching us chemistry concepts. Dr. Doria is all about flair!"

Wirth agreed, and added, "It’s very applicable to real life. I find things more interesting when it’s applicable."

Doria creates these "back-stories" and designs the labs to give students hands-on experience using the basic forensic techniques one would be expected to know starting out in a crime lab. There’s a mock paternity test, where the students use gel electrophoresis to analyze samples of DNA; fingerprint analysis, where they learn techniques used to lift even very old and degraded fingerprints; analysis of gunshot residue to determine parameters like how close the weapon was to the target; mock arson investigations where the students analyze combustion residues; dirt, paper, and fiber analysis; and of course drug analysis.

"If you were to gather a sample of a drug, for instance, cocaine, it will probably have starch in it, and maybe a little bit of sugar," Doria explained. "It’s probably got a little bit of lidocaine, or procaine to make it a little bit less painful. So a sample of cocaine that you would take will only have a small amount of cocaine in it." Doria said that’s true for a lot of drugs that are tested in the crime lab. "If you’re going to analyze the sample, you’ve got to know how to separate out the drug. Because what you really want to know is how much of the drug is in there. We spend a lot of time talking about different techniques you use to separate the ingredients in the sample."

Depending on the samples being analyzed, Doria said the students will either work forwards or backwards in search of the answers to their lab scenario. He pointed out that in an arson investigation many of the clues at the crime scene may have been destroyed by the fire. But that doesn’t mean all of the evidence is gone. "You can look at the thing that’s burning and figure out what you’re going to get, or you can look at the residues, which is what you’d be looking at if you came to a crime scene and took a sample, and work backward from that to figure out what must it have been that burned," he said.

After the students have spent the semester learning all the different theories and techniques, the course concludes with a special challenge. Instead of giving a written final, Doria requires each student to select one of the lab tests they’ve done during the semester and prepare a poster presentation using their test results. They are asked to create their posters as though they are testifying in court on behalf of the prosecution.

"Stuart Smedley, who’s the coroner in Garland County, comes and looks at their posters," Doria said. "He has a great deal of legal experience, and he grills the students. First they talk about the strengths of what they’ve done - here’s the evidence that shows this person probably is guilty of drug possession or arson or whatever it is they’re trying to prove."

Doria said that Smedley then steps into the role of the defense attorney and questions the students again, trying to shoot holes in their analysis. "He’s really trying to get them to look at their poster and say ‘here are where the weaknesses are,’" Doria explained. "He wants them to be very realistic about the limitations of what their evidence shows. It’s a good mental exercise for them."

"[This class] shows how important the forensic investigators are," Martin said. "They’ll bring them in to court cases, and they have to explain all the chemistry behind it and everything has to all be exact, because if the prosecution is going to use you as one of their main supports, you have to be pretty precise."

Even though they’re only partway through the course, Wirth and Martin agreed that the class has given them a new perspective on chemistry and on forensic analysis. What did they find most surprising? "Basically all the things about drugs," said Martin. Wirth agreed, adding "How dangerous it is to make meth, and why people would ever do it!!!" And while neither of them plans to pursue a career in forensic chemistry, they both said the class has also changed their perception of what forensic chemistry is about and how it is portrayed on television. "CSI is a little bit factual, but it’s a lot more work in the real life CSI. Now I watch a show and think, ‘nah, that’s not possible," said Martin.

"For general chemistry and organic chemistry, which are the usual classes that people take, you learn all the concepts and you learn the theory," Doria said. "You do basic experiments, but the experiments for the most part are designed for the class." The forensic chemistry class is very different in that respect. "In this class, you get what you get," he said. "Sometimes, the sample that you get, like the marijuana they’re worked with today - I assumed that it would work pretty well, but then again, maybe it wouldn’t. I was pretty sure they’ll find some [THC], but maybe they wouldn’t." For Doria and the students in the class, this element of uncertainty is what makes the forensic chemistry class so realistic. "That’s real life," Doria said. "You don’t always get the thing you think you’re going to get."