Chemical Education Today edited by
NSF Highlights
Susan H. Hixson
Projects Supported by the NSF Division of Undergraduate Education
Incorporation of GC–MS into an Environmental Science Curriculum
National Science Foundation Arlington, VA 2230
Curtis T. Sears, Jr. Georgia State University Atlanta, GA 30303
Audrey E. McGowin and George G. Hess Department of Chemistry, Wright State University, Dayton, OH 45435
Incorporating modern analytical instrumentation such as GC–MS into an interdisciplinary environmental science program presents many challenges. The most daunting challenge is the variety of disciplines from which students come and their limited understanding of chemistry and chemical analysis. A laboratory component has been added to our environmental chemistry courses to provide students majoring in environmental science, biology, geology, chemistry, and engineering with experience both in the field and in the laboratory. Wetlands restoration projects totaling more than 1000 acres under public management are within 2–10 miles of campus. Some of the sites we use have been developed by the departments of biological and geological sciences. At one site, students have access to a stream and shallow monitoring wells (surface water) and an artesian well (groundwater). In the environmental courses students sample, analyze, and compare water from each source, observing the movement and transformation of selected chemicals. In October of the past three years, students have observed an increase in nitrate concentration resulting from ammonia application in nearby fields during the growing season. The ability of undergraduates to study the organic chemistry of the wetlands has been expanded with the availability of a Hewlett-Packard 5973 Mass Selective Detector and 6890 GC. Several novel experiments developed for environmental chemistry laboratory are designed to investigate the fate of chemicals in the environment. The fate model includes setting up a microcosm in the laboratory to model the environment and limit the number of variables present. The chemical under investigation is added to the microcosm and monitored over a predetermined time period. Environmental fate experiments prevent the boredom and disillusionment experienced by students who are unable to detect their analyte in real samples, even though the absence of the analyte is a desirable result indicative of a clean environment. Projects represent realistic situations that interest and motivate students yet are limited in scope to minimize frustration. An experiment using the fate model has been described recently by Klausen, Meier, and Schwarzenbach (1) for measuring the hydrolysis rate of contaminants in water. The experiment summarized here measures the biodegradation potential of a chemical in soil and is modeled after the EPA Inherent Biodegradability in Soil test (2). This test applies to “volatile or nonvolatile, soluble or insoluble compounds” (2); we have performed it primarily with pesticides, but it also works well on drugs. The best chemicals to use would be environmentally important ones having half-lives on the order of two weeks, with relatively persistent degra-
dation products that can be detected by GC–MS. (Note that the EPA method calls for radiolabeled test materials to be used. We do not use radiolabeled materials.) Our experiment is for a three-week laboratory where students, in small interdisciplinary groups, set up a series of soil biometer flasks (3). Each group is assigned three flasks: one for the test chemical, one for a reference chemical (dextrose or glucose), and one to serve as a control. To each flask, 50 g of soil is added. The test compound is added to the soil in one flask and the reference compound to another; no chemical is added to the soil in the control flask. Each biometer flask contains a small amount of KOH solution for absorption of the evolved CO2 resulting from microbial respiration. On scheduled days, the flasks are aerated and the amount of absorbed CO2 is determined by titration. The amount of CO2 evolved over time from the various flasks indicates the degree of biodegradation or inhibition. Lag periods are frequently observed. In addition, the experiment requires the determination of soil moisture content, field moisture capacity, pH, and texture. At the end of the incubation period, soil samples from the test and control flasks are extracted and the analytes are concentrated using solid-phase extraction. With Standard EPA Methods for GC–MS, the amount of extractable test chemical remaining is determined and the mass spectra of peaks unique to the extracts are examined. The computer library is utilized to identify these unique components, which may be degradation products of the test chemical, although students are encouraged to search the literature for the identity of possible degradation products so they can evaluate the accuracy of the computer library. Students naturally tend to take the lead in areas where they feel more comfortable. Those with more chemistry background tend to lead in the sample analysis, whereas those taking more courses with biology or geology emphasis are more comfortable with the preparation and characterization of soils. They learn from each other as they work and discuss each aspect of the project. In their group presentation at the end of the project, students present evidence to the class in support of their conclusions. Depending on the experimental parameters, students may compare the biodegradability of a chemical in various soil types or the relative biodegradabilities of various chemicals in the same soil. Since the entire class becomes familiar with the subject in greater depth, lively discussion ensues during the presentations and students feel confident to discuss their results and question the results of others. Students with an education in the environmental sciences must be familiar with GC–MS as an analytical technique,
JChemEd.chem.wisc.edu • Vol. 76 No. 1 January 1999 • Journal of Chemical Education
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Chemical Education Today
NSF Highlights including its applications and limitations, and be able to interpret information gained from GC–MS investigations. They learn how to organize and evaluate analytical data properly. They learn the proper use and significance of surrogate standards, spikes, internal standards, blanks, and replicates. Percent recoveries and minimum detection limits are calculated. A feel for the actual amounts of pollutants and the complexity of the matrices likely to be encountered in environmental samples is cultivated. Students will learn to appreciate the identification both in terms of finding target analytes and in obtaining at least an initial characterization of totally unknown components. They acquire an appreciation for the importance of sample collection and preparation for the accurate analysis of environmental samples. As the students begin to realize the true complexity of environmental samples, they will appreciate the ability of the mass spectrometer to give information about coeluting components. Overall, students learn both the power and limitations of using GC– MS as a tool to detect and analyze environmental pollutants.
At the end of the course typical student comments are very positive, especially with regard to hands-on use of the instrumentation. A suggestion for improvement included “more time in lab”. Acknowledgment This work was partially supported by a grant (DUE 9650817) from the National Science Foundation Division of Undergraduate Education Instrumentation and Laboratory Improvement Program. Literature Cited 1. Klausen, J.; Meier, M. A.; Schwarzenbach, R. P. J. Chem. Educ. 1997, 74, 1440–1444. 2. OPPTS Harmonized Test Guidelines; Series 835-3300; available through the EPA’s WWW site, http://www.epa.gov/epahome/ research.htm at URL http://www.epa.gov/docs/OPPTS_Harmonized/ 835_Fate_Transport_and_Transformation_Test_Guidelines/Series/ 835-3300.htm (accessed November 1998). 3. Bartha, R.; Pramer, D. Soil Sci. 1965, 100, 68–70.
American Chemical Society Council Committee on Divisional Activities Bonnie Lawlor, Chair 1155 Sixteenth Street, N.W. Washington, D.C. 20036 September 18, 1998 Sr. Mary Virginia Orna, Chair Division of Chemical Education Chemical Heritage Foundation 315 Chestnut Street Philadelphia, PA 19106-2072 Dear Sr. Mary Virginia, On behalf of the Council Committee on Divisional Activities (DAC) I want to congratulate you, your fellow Officers, and all your Division Members of the 75th anniversary of the Journal of Chemical Education. It is a major milestone for an essential publication that has had a positive impact on educators and students alike. Almost all chemists today have been touched by it in some way! We wish you continued success with your publication and with your Division as well. The Division of Chemical Education has been a positive example to all the Divisions of the Society with its consistently high standards of achievement and performance. Congratulations on a job well done. With Sincere Regards, Bonnie Lawlor, Chair Committee on Divisional Activities cc: Michele Gandy, DAC Staff Liaison Christine Pruitt
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Journal of Chemical Education • Vol. 76 No. 1 January 1999 • JChemEd.chem.wisc.edu
