In the Laboratory
A Forensic-Themed Case Study for the Organic Lab Michelle A. Boucher Department of Chemistry and Biochemistry, Utica College, Utica, NY 13502 Kimberly Musa Specht* Department of Chemistry and Biochemistry, Denison University, Granville, OH 43023; *
[email protected] This laboratory exercise fosters student interest in chemistry by creating a “real-life” problem in a subject made popular through the media: forensics. There is substantial interest in developing forensics-related labs, as shown by recent articles in this Journal (1), as well as labs that engage students in problem solving and cooperative learning (2). This problem-based collaborative-learning exercise introduces forensics themes using basic organic chemistry methods. Students are given “evidence” collected from a body retrieved from a lake and told the apparent cause of death was drowning. Students are then asked to examine this evidence using typical organic chemistry techniques to determine the likelihood of “foul play”. This laboratory has evolved over four years and was inspired by a case study presented in the Journal of College Science Teaching (3). The current design outlines a reliable procedure for sample preparation and a student procedure that is adjustable for different levels of student experience. This laboratory promotes teamwork, asking students to allocate jobs and integrate and present the results (4). It also develops skills in experimental design, encourages students to determine the appropriate techniques and tests, and introduces the use of data as a stepping stone to lead to further analysis (5). We have designed this laboratory as a cumulative second-semester experience in which the students work with little formal guidance from the instructor to collect data from the evidence provided. Taught as an end-of-semester lab, this exercise can also be used to assess skills at wet organic techniques. Each student team is provided with a bag of “evidence” from the crime scene, which includes a sample of water from the lake in which the body was found, samples taken from the body (water from the lungs, a square of fabric from the clothing, fingerprints), a label from the bottle found at the scene, and GC–MS data of compounds found in a blood sample from the body. Students also receive a report sheet in which they list their data, their conclusions from the data, and their suspected cause of death. The students are expected to remember the different ways they have learned to attack chemical problems and to apply them to this situation: extraction from both solids (removal of organics and inorganic salts from the clothing) and liquids (removal of organics from the aqueous samples), IR spectroscopy of organics retrieved from clothing and aqueous samples, qualitative tests (silver nitrate precipitation of chloride to test for the presence of chloride in the water), fingerprint resolution (using ninhydrin stain), and literature searching (SciFinder, Scopus, or Google Scholar) of the relevance of GC–MS data. Although the authors typically run this lab asking students to devise their own procedures, with more guidance this lab could also be used to introduce the technique of extraction or IR and MS.
Experimental This laboratory can be completed in one three-hour lab period. Typically students work in groups of three to four. Students self-allocate the various tests of samples and then meet as a group to discuss their findings. The water samples (“lake” and “lung”) are prepared as aqueous solutions of appropriate chemical type and loading (see the online material). The “lake water” samples contain organics (urea, malonic acid, and benzophenone) that are suggestive of agricultural waste. Urea is an obvious choice, malonic acid is used as a compound with the same functional groups (COOH, Csp3−H) as fatty acids with the appropriate aqueous and organic solubility (6), while benzophenone is suggested from the literature (3). These organics can be extracted and visualized utilizing IR. The “lung water” contains chloride and no organics, which the students should immediately recognize as being related to chlorine-treated water found in pools. In swimming pool treatments, chlorine reacts with water to form hypochlorous acid (the disinfecting reagent) and chloride ions (7). It adds interest to use actual samples from a pool to show that treatment with silver nitrate yields large quantities of precipitate (8). The clothing sample contains the “lake water” organics, which can be extracted, dried, and visualized in the IR, and chloride so that the treatment of an aqueous extract with silver nitrate yields large quantities of precipitate. The “bottle label” found at the scene is prepared with two different thumb prints that are resolved using ninhydrin stain (9). In introducing the ninhydrin test, we typically use the opportunity to discuss the mechanism of reaction with amino acids to form Ruhemann’s purple (10). The GC–MS data show acetaldehyde, 4-hydroxybutanoic acid, and tetracycline in the recovered body’s “blood”. To determine the importance of this data to the “case”, students need to perform a literature search. From the data showing the lung water to be different from the lake water, students are able to deduce that the victim drowned in a body of water different from the lake in which it was found. The data from the cloth sample are consistent with this conclusion, showing evidence of both bodies of water. Although students cannot always determine that only one of the two fingerprints on the label came from the deceased, the fact that there are two different right-thumb prints suggests two people had handled the bottle. The literature search reveals that acetaldehyde was evidence of alcohol consumption (11), tetracycline is an antibiotic (12), and the 4-hydroxybutanoic acid is evidence of either recreational drug use or of potential foul play (a commonly abused recreational and date-rape drug) (13). Based on the evidence, groups determine that there is a high likelihood that the death was not a simple accidental drowning—there was at least movement of the body involved.
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 7 July 2009 • Journal of Chemical Education
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In the Laboratory
Hazards Because only small quantities of benzophenone, urea, ninhydrin, malonic acid, bleach, silver nitrate, 2-propanol, dimethyl sulfoxide, and methanol are used in this experiment, the risks are minimized owing to scale. Benzophenone, urea, ninhydrin, and dimethyl sulfoxide are irritating to the eyes, respiratory system, and skin. Malonic acid is toxic and harmful if inhaled or swallowed. Silver nitrate is an oxidizing agent and may be harmful if inhaled or swallowed and is irritating to eyes and skin. Ether and 2-propanol are flammable and irritating to the eyes, respiratory system, and skin. Methanol and petroleum ether are flammable and toxic if inhaled, swallowed, or absorbed through skin. Bleach is corrosive, may cause burns, and is irritating to the respiratory system. Normal laboratory safety precautions should be taken. Discussion Since this was designed as an end-of-semester wrap-up activity, students were given few initial instructions. Working in teams, students quickly identified ways to divide responsibility for the evidence. They held brainstorming sessions and then assigned portions of the evidence according to individual desires and personal strengths. Most students were able to determine an experimental procedure, occasionally requiring hints, such as, “What type of solvents have we used to previously extract organics from aqueous solutions?” Students were cautioned to consider sample size and some students chose to repeat procedures. During the integration of results, students were comfortable challenging each other and requesting further explanation. A few students even approached the tests with ideas of what results might mean (e.g., differences in water from the lake and from the lungs would point to the possibility of the body having been moved from the drowning scene). Throughout the semester students had been encouraged to think ahead in the laboratory and imagine what various results might indicate; the link of this laboratory to a CSI-style case file aided in encouraging this behavior. This laboratory worked well as a low-pressure assessment. Students who had mastered the techniques were able to get good results. Students who had more trouble with the techniques tended to get more ambiguous results but were still able to “solve” the case. As long as at least one group got good data, students were able to self-assess, define the source of their trouble, and then repeat that procedure following experimental suggestions from their peers. Students were asked to report their collected data, their conclusions drawn from the data, and their hypothesis as to the cause of death. They were very clear as to the difference between what were categorized as data (this IR has a C−H peak, this IR does not) and what were conclusions (the lake and lung water samples were different). Students generally made clear and reasonable conclusions based on the evidence. They also distinguished between the conclusions (deduction) and the cause of death (complete assumption). Many chose to hypothesize scenarios about the cause of death and how the body had been brought to the lake. Students were able to suggest further tests
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that could be used to verify particular results, corroborate their conclusions, and to further test their scenario hypotheses. Post-lab, students expressed an understanding for the need of forensics labs to have strict procedures to ensure accuracy. They also indicated a greater appreciation of the difficulties in obtaining accurate and reproducible results. In evaluations, students appreciated the application of the lab to more familiar scenarios and that this connection made the lab enjoyable. Acknowledgments We thank Tom Evans for his guidance in preparing this manuscript and Tom Evans, Jordan Fantini, and Sonya McKay for testing this laboratory in their courses. Literature Cited 1. (a) Grove, N.; Bretz, S. L. J. Chem. Educ. 2005, 82, 1532–1533. (b) Hoffman, E. M.; Beussman, D. J. J. Chem. Educ. 2007, 84, 1806–1808. (c) Beussman, D. J. J. Chem. Educ. 2007, 84, 1809–1812. (d) Henck, C.; Nally, L. J. Chem. Educ. 2007, 84, 1813–1815. 2. (a) Polik, W. F.; Larive, C. K. J. Chem. Educ. 2008, 85, 484–487. (b) Mahan, E. J.; Nading, M. A. J. Chem. Educ. 2006, 83, 1652– 1653. (c) Horowitz, G. J. Chem. Educ. 2003, 80, 1039–1041. 3. Konaklieva, M. Journal of College Science Teaching 2004, October, 10–13. 4. Dinan, F. J.; Szczepankiewicz, S. H.; Carnahan, M.; Colvin, M. T. J. Chem. Educ. 2007, 84, 617–618. 5. Gaddis, B. A.; Schoffstall, A. M. J. Chem. Educ. 2007, 84, 848–851. 6. Seidell, A. Solubilities of Inorganic and Organic Substances, 2nd ed.; D. Van Nostrand Company: New York, 1919; p 399. 7. Salter, C.; Langhus, D. L. J. Chem. Educ. 2007, 84, 1124–1128. 8. Brown, T. L.; LeMay, H. E., Jr.; Bursten, B. E.; Murphy, C. J. Chemistry The Central Science, 11th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, 2009; pp 125, 753–754. 9. United States Department of Justice. Processing Guide for Developing Latent Prints. http://www.fbi.gov/hq/lab/fsc/backissu/ jan2001/lpu.pdf (accessed Feb 2009). 10. Jones, Maitland, Jr. Organic Chemistry, 1st ed.; W. W. Norton: New York, 1997; pp 1357–1358. 11. Lieber, C. S. Alcohol Research & Health 2003, 27, 220–231. 12. The Merck Index, 13th ed.; Merk & Co., Inc.: Whitehouse Station NJ, 2001; p 9272. 13. Chappell, J. S.; Meyn, A. W.; Ngim, K. K. J. Forensic Sci. 2004, 49, 52–60.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/Jul/abs847.html Abstract and keywords Full text (PDF) with links to cited URL and JCE articles Supplement Student handouts
Instructor notes, including sample spectra and suggested answers
Journal of Chemical Education • Vol. 86 No. 7 July 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
