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Robert Q. Thompson Paul L. Edmis ton he body of Walter Smith, an electrochemistry professor, is found buried at a construction site on a college campus. Could a respected member of the faculty have committed the murder? A teenage girl, Rebecca Ferris, is discovered dead by the side of the country road, an apparent hit-and-run victim. Is Bradley Kimmer, a local man whose home is not far away, guilty of vehicular homicide? During the past three years, the task of solving these and other “crimes” has been put to analytical chemistry students at the College of Wooster and Oberlin College—two private, four-year undergraduate colleges in northeastern Ohio. Cooperative project laboratories that provide students with a multiweek, researchlike, capstone experience have replaced conventional, one-instrumental-method-a-week experiments. Although the colleges developed their projects independently, they are analogous.
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Similar project labs that focus on environmental issues have been introduced in U.S. schools in recent years, such as sampling and analysis of urban air (1), surface water (2, 3), aquarium water (4), and soil samples for lead (5). In addition, for more than a decade, John Walters at St. Olaf College and others have had students play roles as part of cooperative efforts in the laboratory (6, 7 ). In this article, we describe the use of crime scene investigation and forensic science as the vehicle for project laboratories in analytical chemistry courses. We outline how the forensic project lab works, and, in the tradition of a real mystery, we describe the experiences of two groups of students as they try to solve hypothetical murders.
Course context At both institutions, the forensic lab takes place at the end of the first analytical chemistry class. The courses are 13–15 weeks in length, with three 50-min classes and one 3-h lab per week. The classes are typically populated by 20–30 juniors and seniors (~40% male, 60% female; ≤10% international students) majoring in chemistry, biochemistry, or a related science. Both courses have general chemistry as a prerequisite and may be followed by intermediate-level classroom and lab experiences in analytical science. Classroom material includes elementary statistics, acid–base equilibrium and activity concepts, absorption spectrophotometry, GC, LC, and electroanalytical techniques. The forensic project lab builds on 8–9 weeks of quantitative lab skills development, including glassware calibration, data handling, titrations, absorption spectrophotometry, poten-
tiometry, and chromatography. A practical exam immediately follows that tests most of the quantitative lab skills that students have developed up to that point.
The case of the trampled teenager The facts of the case were available to the students at the project’s secure Web site: testimony from witnesses and suspects; reports from the police, fire fighters, and the coroner; and even some crime scene photos and a map. A teenage girl, Rebecca Ferris, was found dead by the side of the road, an apparent hitand-run victim. The suspects are Simone Argones, a classmate of the deceased who remorsefully has admitted guilt; Peter Bredon, a neighbor and owner of a car with a damaged windshield, and Bradley Kimmer, a local man stopped for driving drunk the night of the death. No one saw the accident, but four witnesses have shed some light on the day’s events. It is the class’s task to understand what happened to Rebecca through examination of the physical evidence. Week 1. The dozen Oberlin students in the Tuesday lab section gather in a classroom to begin. The instructor informs the group that they will act as the prosecution and state crime lab, and the Wednesday lab group will play the role of defense and private testing lab. The students survey the physical evidence from the crime scene and from the suspects, which is already collected and organized in a lab drawer (the evidence locker). The students then discuss the case and compile a list of names, tests, and evidence on the chalkboard. To tackle the project, the students divide into five groups of three in accordance with the sets of physical evidence. The indi-
Edmiston assists two of his students in the lab who are performing an FT-IR microscopic examination of fibers.
vidual groups analyze blood samples from Kimmer and the victim for ethanol, compare green fabric samples found on the front bumpers of the suspects’ automobiles with the green shirt the victim was wearing, examine headlamp glass by refractive index and by trace magnesium content, test the victim’s shoes for an herbicide to determine whether she had been walking through a cornfield that parallels the road where she died, and investigate the victim’s blood and a bag of white powder found in Bredon’s car. (The bag of powder is something like caffeine or sugar, but fictitiously marked by the professor as cocaine or another illicit drug; students check their spectra against reference spectra.) The Web site gives brief directions for each of these analyses. (More detailed instructions are available from the teaching assistant and the instructor.) Week 2. Each group comes this week to lab with a “book knowledge” of the particular techniques and instruments that they will use. The students receive hands-on experience in operating the equipment (Table 1) and handling the samples. Standards are used to check and optimize the instruments. During this time, the instructor wanders around, assists students in running instruments, and gives encouragement but otherwise does not interfere. Week 3. The class conducts a final set of standard reference tests to check the accuracy of the method and, if time allows, begins testing the forensic samples. At the end of lab, the whole group meets to exchange information. The students discover that some results point to Kimmer as the likely perpetrator. He was legally drunk according to the students working with the gas chromatograph, and the bit of cloth found on his bumper matches the victim’s shirt. Week 4. The students finish their analytical tests, and many begin to organize their data and results. They are under pressure to “formally charge” and “arrest” someone by the end of today’s lab, so that the defense will have time to prepare its case. As the results come in, the picture, unfortunately, gets murkier. The analyses show that the victim’s blood contains cocaine, and atrazine found on her shoes indicates that she was in or around the adjacent cornfield just before death. Results also show that glass found at the crime scene matches glass from both Kimmer’s headlight and Bredon’s windshield. After much discussion, the students decide to charge Kimmer with vehicular homicide. The ground rules of the upcoming “trial” state that the students must present all of their evidence and be truthful, but they can emphasize some results and downplay others. The prosecution group will focus on Kimmer’s intoxication, the broken headlamp, and the fabric from the victim’s shirt found on Kimmer’s bumper. Week 5. Although a few people are still finishing up their tests, most prepare large, detailed posters that will serve as reports and visual aids during the trial. They also read about the techniques they have used and prepare questions to ask the other group; questions that might test the other lab’s knowledge of the instruments and methods. A member of each group is chosen to deliver the opening statement and another to give the closing address. Each student will present his or her own
Table 1. Testing of forensic samples for Rebecca Ferris case. Evidence
Analyte or characteristic
Blood (simulated) Ethanol Drugs of abuse Fabric Composition Color Glass
Refractive index Magnesium
Shoes Powder
Atrazine Drugs of abuse
Techniques Headspace analysis GC GC/MS FT-Raman spectroscopy Visible, diffuse reflectance spectroscopy Microscopy Atomic absorption spectrophotometry Solid-phase extraction; LC FT-IR
findings, and some will have the opportunity to question corresponding members of the other side. The trial. The posters are mounted on the wall outside the “courtroom” (classroom) prior to the 3-h session, including the trial, held on a Saturday morning. Now the students have a chance to see what the other side plans to present and to plan their own rebuttals. The teams have a quick strategy session before heading into the courtroom. The judge is the course instructor, and the jury consists of two Oberlin faculty members from outside of natural sciences and a senior chemistry major who took the course last year. The trial proceeds according to a predesigned format, similar to that used in actual criminal trials, except that time limits are set for each phase and the jurors are allowed to ask for clarification at the end of each presentation. Each side presents its contentions. The prosecution argues that Kimmer was drunk when his car hit Ferris, who was walking along the road. The defense contends that Ferris was under the influence of cocaine and dashed from a cornfield into the path of Kimmer’s car. After considering the arguments and rebuttals, the jury finds the defendant guilty as charged.
The case of the poisoned professor Dr. Walter Smith was hired to teach a special one-year course in electrochemistry at Wooster; however, shortly after moving to the college, he was found dead and buried in a shallow grave about to be covered by the concrete foundation for a new chemistry building. The coroner has determined that Smith was poisoned by a rare and complex organic substance not readily available to the public. Law enforcement immediately suspects that a chemistry faculty member is the culprit, but repeated interrogations fail to uncover the guilty party. Consequently, the physical evidence was submitted for analysis to what seemed to be an unbiased group—the analytical chemistry students. The students are distributed into two lab sections of 13–18 each, and both groups are assigned the role of prosecution and instructed to work cooperatively. What one group begins on Tuesday, the other continues on Wednesday, and so on. Each lab section further divides into teams of 2–4 to investigate a
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particular sample. With students working together, the analysis of each sample type progresses quickly. Week 1. The students examine all of the physical evidence from the crime scene. A handful of short pink fibers on Smith’s coat appear out of place, and several short hairs and soil were collected from the coat pockets. Students also identify what appears to be a stain on the coat made by a clear and viscous liquid. It has hardened to a crusty film and is presumed to be saliva residue on the basis of comparisons to stains prepared on a similar fabric. All of the samples are carefully collected and stored in labeled bags. One student is elected as prosecutor and organizes and coordinates the class work. Week 2. Students collect more samples after the instructor demonstrates some sampling methods. Because the source of the fibers found at the crime scene is unknown, students sample carpets in faculty offices, homes, and automobiles. Hair is snipped from faculty members’ heads and pets. Soil samples are collected from the floor of faculty offices, around faculty homes, campus parking lots, and the construction site. The stain on the coat is positively identified as saliva through immunological experiments; however, it is not the saliva of the deceased. Because the saliva contains enough epithelial cells from the cheek to perform DNA typing, comparative cheek cell samples are taken from all faculty members by having them rinse their mouths with saline solution. Week 3. Analyses of all the crime scene evidence and suspects’ samples are completed. Students conduct tests appropriate for the evidence and, where possible, with which they have experience (Table 2), while the instructor provides instruction and answers any technical questions, but otherwise stays in the background. A pink blanket has been found in the trunk of a car owned by Professor A—an organic chemist with the ability to synthesize the unusual poison. Fibers are examined and compared using visible light microscopes, and those fibers that visually match are analyzed with an FT-IR microscope to determine the chemical composition. Professor A’s pink blanket matches the color and composition of the pink fibers found on the victim’s coat. Mean-
while, soil samples tested for pH and iron content link the soil found in Smith’s coat with soil found at several locations, including Professor A’s driveway, but not the construction site. Unfortunately, the hair analysis is inconclusive. The shape, color, and morphology reveal that it is animal hair. IR analysis and other tests cannot distinguish among the collected hair from faculty pets. Finally, students use polymerase chain reaction and electrophoresis on a high-resolution agarose gel to analyze and size the length of a short tandem repeat in DNA. They determine that the saliva found on Smith’s coat matches that of two faculty members, including Professor A. However, because only one tandem repeat segment is analyzed, the probability of the DNA matching anyone in the population is high—1 in 6 have DNA that matches that found on Smith’s coat. Nevertheless, at the end of the week, the students charge Professor A with the first-degree murder of Smith. The trial. Professor A’s trial occurs during the class’s scheduled 3-h final exam period. Presiding over the case are two real police detectives, one from the city police and the other from the county sheriff’s office. The jury is composed of seven undergraduates of various ages and backgrounds, adults from the Wooster community, and nonchemistry majors. The instructor and two other Wooster analytical chemistry professors handle the defense of Professor A. (Even Wooster’s president, who is clearly “worried” about the fate of Professor A, attends!) The prosecution focuses on the fiber and DNA evidence. The defense spends a good amount of time cross-examining the students with questions about S/N levels, replicate measurements, and confidence intervals. Students are asked to defend the principles and practices of the techniques used. A turning point in the trial occurs when the defense calls several surprised students to the stand and produces a videotape showing that some evidence was scattered on the floor and then handled with bare hands. One of the students is asked how the group could conclude that the fiber spectra are not really floor dirt or fingerprint grease? The prosecution fights back in the closing arguments by arguing that several peaks in the IR spectra are consistent with a particular type of polymer, not dirt or grease. After instructions from the judge, the jury deliberates for 30 min, returning a verdict of not guilty. The jury finds that too few replicate samples were tested to have confidence in the results. Immediately after the verdict is read, Professor A confesses to the murder. The announcement affirms the students’ work and conclusions about the case even though Professor A is now outside the reach of the law. (In a bizarre twist, two years later the “guilt-racked” course instructor “kills” Professor A. That year’s analytical class uses a litany of analytical techniques to build an overpowering case and successfully convicts the murderer.)
Some evidence was scat tered on the floor and then
Table 2. Testing of forensic samples for poisoned professor case. Evidence
Analyte or characteristic Techniques
Soil
pH Iron Composition Physical properties Proteins DNA Appearance
Fibers Saliva stain Hair
Potentiometry Visible spectrophotometry FT-IR microscopy Solubility, melting point Immunological tests Short tandem repeat DNA analysis Microscopy
A scene from a trial. Wooster analytical chemists Richard Bromund and Theodore Williams can be seen at the far right in the front row next to the lead attorneys. A retired court judge presides.
Comparison of approaches While both approaches to the project labs are effective and engaging, they are distinctly different. At Oberlin, the instrumental analysis portion of the course is performed within the context of crime-solving and forensic chemistry; the Wooster approach emphasizes criminal investigation and concomitant problem solving more than learning instrumental techniques. This purposeful difference in focus changes how each school implements the lab. Wooster students must find and collect evidence from suspects and from items found at the crime scene, just as criminalists would do in a real investigation. They learn to make careful searches and to be observant. Students are not told what sample component to determine or what tests to perform. From reading the literature, peer discussion, prior knowledge, and instructor assistance, the students should have enough information to choose proper analytical methods. Valuable lessons are learned, but at the cost of time away from the lab. However, students are encouraged to perform simple tests and work with familiar instruments so that they can begin and complete testing quickly. The goal is to uncover facts of the case. Because the Wooster lab sections perform the analyses sequentially, a pair of students will not experience firsthand all of the analytical steps. Students learn to share and depend on each other’s data and conclusions. Having the instructor identify and empower particular students to take leadership roles (i.e., as lawyers and group leaders) is key to fostering successful teamwork and communication within and between lab sections. Finally, because the Wooster lab sections work together as the prosecution team, the defense challenge must come from the in-
structor. Thus, the instructor has the difficult task of balancing being helpful and forthright with planning an attack on the students’ work. Even though students relish the opportunity to outwit their professor, the professor must be careful that the competition does not spoil his or her relationship with students. On the other hand, at Oberlin, all samples, a list of analyses to perform, and brief descriptions of the analytical methods are provided. The students must add the details of the experiments. Instrumental techniques are used exclusively, and students are encouraged to gain experience with unfamiliar equipment and methods. Consequently, students need more time to learn to use the instruments and to check system performance, and the instructor is in high demand for instruction and assistance, especially during the first lab sessions. Learning about instrumentation and chemical analysis remains the focus. Each group of students performs each step of the analysis. This is important when learning techniques and instrumental principles is stressed. Unlike Wooster, the two Oberlin lab sections compete rather than cooperate. Oberlin trades learning process skills for more lab experience. The instructor can relate to the students more naturally, because he or she acts as an impartial resource and a trial judge. Here, the competition is between students, which may be healthier for the class; on the other hand, it is important that the competition not escalate too far.
Final verdict The objectives of both project labs are for students to experience one or two instrumental techniques in depth; learn to design, perform, and assess lab experiments; work as a team;
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Table 3. Additonal samples and analytical techniques used in the forensic projects. Evidence
Techniques
Gunshot residue
Atomic absorption spectrophotometry, scanning electron microscopy Visible reflectance, FT-IR microscopy, FT-Raman UV–vis, LC FT-IR, UV–vis Thermal analysis, FT-IR Liquid- and solid-phase extraction, GC/MS Fluorescent visualization Atomic absorption spectrophotometry, titrations GC, GC/MS
Clothing Pen inks Plastic fragments Tire fragments Food (poisoned) Fingerprints Metals Arson samples
present experimental results orally or in poster format; and convince nonscientists of scientific conclusions. The degree to which these objectives are met is assessed, and a single project grade is assigned for each student. “The premise that ‘students learn more if we teach them less’ is the basis for a cooperative learning technique commonly referred to as problem-based or inquiry-based learning” (8). Our students are exposed to fewer instrumental techniques (one or two) than in a conventional lab (four or five in a fourweek lab). In truth, we are still somewhat uncomfortable with this reduction, but we have found that students are more engaged, do more of the background reading, and better understand the meaning of the experimental results. For most students, the project lab provides an amount of learning that more than balances what is lost in coverage, and they comment more positively about the experience. A recent study of contextbased lab experiments made similar conclusions (9). “Students design their own experiments, so they are more prepared to do them and more interested because they are creatively involved in the activity.… By designing their own experiments, students must think for themselves about what they are doing and why. They are not rotely following someone else’s instructions in which they may do an activity without knowing why” (8). Students are required to work within a framework that forces them to think more clearly about an analysis. For instance, they are presented with a limited amount of sample and, consequently, must perform the experiment correctly the first time. They realize that performing control experiments or using test samples are valuable. Faculty, too, must anticipate student needs and be flexible, within reason, providing equipment and reagents to allow student innovation. Students must be given enough time to make and recover from mistakes. A project that lasts 5–6 lab periods works well. The analytical chemistry students easily and very willingly form teams and smaller groups to complete the necessary analyses and prepare the case. They seem well prepared by prior college classes or earlier training to debate, organize, and engage in discussion. The instructors have had to do little to pro-
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mote the cooperative activities. The collegial environment, students knowing each other from other science classes, and the relatively small class sizes probably help. The project lab also provides opportunities for students to express their leadership, both behind the scenes in the lab and at the mock trial. For instance, we always have willing volunteers to act as lead attorneys. The mock trial activity motivates students to better understand what they are doing. They are told that they must clearly explain their research, so that the nonscientists on the jury can understand the significance of the experiments and the most important conclusions. In particular, students learn that accuracy, precision, and statistical analysis are important to the validity of the claims they make on the witness stand, especially when their statements may be challenged by their instructor, nonscience faculty, or other students. The forensic project lab is quite flexible and can be accomplished with just about any type of concocted sample that supports the story line. Because of the freedom in sample choice, the type and number of chemical instruments are not crucial. Evidence can be chosen that is suitable for analysis by the instruments on hand, while remaining creative and challenging to the students. Table 3 lists some of the other analyses that we have performed over the past three years. Our students certainly have found the exercise to be educational as well as enjoyable. And we as instructors have a lot of fun, too! We plan to continue our “criminal activities” and to stretch our students’ intellect and imagination to their limits. We have even discussed an intercollegiate version of the project lab, with Oberlin students pitted against Wooster students. If it makes the challenge even more effective and engaging, we are all for it. Robert Thompson acknowledges the financial support of a grant to Oberlin College from the McGregor Fund and Donald Oresman (OC ’46), and thanks Ruth E. Hook (OC ’00) for her significant contributions to the project.
Robert Q. Thompson is a professor at Oberlin College with research interests in forensic chemistry, including explosives residue analysis, solid-phase extraction, and chromatography. Paul L. Edmiston is an assistant professor at the College of Wooster with research interests in developing chemical sensors using molecular imprinting techniques and examining structure–function relationships in proteins. Address all correspondence to Thompson at Oberlin College, Chemistry Department, 119 Woodland Ave., Oberlin, OH 44074 or
[email protected].
References (1) (2) (3) (4) (5) (6) (7) (8) (9)
Hope, W.; Johnson, L. P. Anal. Chem. 2000, 72, 460 A–467 A. Werner, T. C.; Tobiessen, P.; Lou, K. Anal. Chem. 2001, 73, 84 A–87 A. Juhl, L.; Yearsley, K.; Silva, A. J. J. Chem. Educ. 1997, 74, 1431–1433. Hughes, K. D. Anal. Chem. 1993, 65, 883 A–889 A. Fitch, A.; Wang, Y.; Mellican, S.; Macha, S. Anal. Chem. 1996, 68, 727 A–731 A. Jackson, P.T.; Walters, J. P. J. Chem. Educ. 2000, 77, 1019–1024. Voress, L. Anal. Chem. 1991, 63, 347 A–350 A. Ahern-Rindell, A. J. Journal of College Science Teaching Dec. 1998/ Jan. 1999, 203. Henderleiter, J.; Pringle, D. L . J. Chem. Educ. 1999, 76, 100–110.
