Integrating Research Instrumentation with the General Chemistry Curriculum Part I: Mass Spectrometry Karen E. Eichstadt Ohio University, Athens, OH 45701
Chemical educators who teach a t the introductory level are faced with the task of presenting chemistry as a multifaceted and dynamic discipline. The need to revamp chemistry curricula at all levels is well-documented (13). In addition to addressing the basic principles, the skillful lecturer should incorporate such ancillary topics as career options, industrial applications, and research. In planning a well-rounded general chemistry course, a n effort should be made to provide meaningful experiences that will remain with the student long after the final exam. Although chemical research may seem far-removed from the freshman classroom, these students, the technologists and voters of the future, should be helped to recognize the value of research, if not also its technical merit. Video presentations can be used to bring a diversified view of into the lecture hall, including reports of imchemistry (4) portant historical discoveries or interviews with practicing chemists from all areas. Also, authors frequently recommend successful research experiments that they designed for students in introductory courses (5). We have developed a program with five specific goals that adds a personal dimension to our students' exposure to research. To introduce students to a "high-tech"research technique, using both technical language and an appmach that are appropriate for a freshman-level chemistry class. 7 0 nrquamt students wth a rcscnrch chrrnlst as n "real"person who 1s txr>tcdnhout cherniary. 'lh pmvlde a t u u r of an rn.itrurnmt facduy, ao r h s t ~tudenLse m see the type of equipment that a university needs to support its research. To show how the technical results of research techniques are relevant to freshmen chemistry by integrating them with freshman topics. To make the project attractive and worthwhile to the students.
Many different research techniques could help the instructor achieve these goals, including mass spectrometry,. molecular modeling of proteins, and ultrahigh vacuum experiments. We chose mass spectrometry for i t s convenience. The Nature of the Project
A three-part exercise entitled "A Glimpse of Mass Spectrometry" was designed for students enrolled in the third quarter of a one-year, nonmajor course that surveyed organic and biological chemistry. It was scheduled for a time during the quarter a t which students were beginning to appreciate the large variety of organic compounds possible and asking such questions as "How does a chemist really know what a sample is?" Certainly there a r e numerous textbook and laboratory answers to the question, but a modern research scientist with only a few micrograms of sample probably would use an instrumental method of analysis. For some problems, mass spectrometry would be the method of choice. 48
Journal of Chemical Education
Part I: Presentation by a Guest Researcher
We invited a university research colleague, an authority on mass spectrometry, to address the class for part of the regularly scheduled lecture. Our purpose was two-fold: to provide information and to convey the enthusiasm researchers experience while unravelling the structure of a unique chemical compound. The special topic, mass spectrometry, was introduced at a natural breakine ooint in the course. Itealizme that the majority of the s&ients would know absolute6 nothing about the subiect, we distributed a handout with kev information. The -guest lecturer coordinated the special-topic material to comply with the course instructor's desire to minimize the number of new terms introduced. Table 1 lists the glossary that was included in the three-page handout. The students were told that all the essential information to be presented was included in the handout. They were asked to listen to the presentation without becoming preoccupied in taking notes. The guest was introduced in the fashion typical at research seminars and was welcomed by the general chemistry students. The guest shared with the students personal experiences in which mass spectrometry provided insight into the structure of an organometallic molecule. For most students this was the first, and perhaps only, opportunity to hear a research chemist discussing individual work. For students who have not yet selected a career, the personal input was especially valuable. During the presentation, the guest emphasized key terms on the handout and drew generalizations. For example, any mass spectrometer, regardless of how fancy, carries out three tasks: ionization, separation, and detection. Since molecules break into fragments in predictable ways, identifying their key fragments can lead to their "reconstruction", and thus their identification. Not all the peaks must be identified. After the short, 20-minute presentation, the guest exoerienanswered a few auestions concernine .. ~ersonal . ces, such an "Were you really sure you had the desired compound?" The guest then left the lecturc hall so that the regular course instructor could funher explain or reinfurce ideas, thus making the lecturc consistent with the background of the students. We think this immediate follow-up by the course instructor is necessary to avoid overwhelming the students. We also recommend keeping the time alloted for the guest brief. Part 11: Tour of the Instrument Facilities
A tour of the instrument facilities was conducted outside regular class time. Arrangements were made for the 160 students to tour in groups of 20. This was the most difficult part of the project to organize, but it was necessary because our instrument is housed in a small room that can
Figure 1. Format for student "quiz" accommodate only 20 students. At the introductory lecture, the students were given the master plan (Fig. 1) in the form of a "quiz" (6).Attached to the plan was a response card that allowed students to indicate their first, second, and third preferences for the time of their tour. Surprisingly, t h e students' requests gave a schedule we could manage. The tour-group rosters were posted. The actual tour was a 30-minute demonstration of our instrument room that was conducted by a researchstudent and the staff technician. Both were familiar with the handout material, and both made an effort to use the terms from the introductory lecture (Table 1). The students had already used paper chromatography i n a previous laboratory experiment, so the concept of chromatographic separation was familiar to them. The parts of the instrument were identified, and a sample was injected. We chose to demonstrate a mixture ( 1 : l benzene:toluene) t h a t was separated by gas chromatography ( G C ) before entering t h e m a s s spectrometer (Fig. 2). The actual experiment was designed to take five to seven minutes from injection to read-out. This allowed ample time to explain the processes and answer a few questions. Table 1. Glossary for the Three-Page Handout,"A Glimpse of Mass Spectrometry"
cation
The most intense peak, arbitrarily assigned an intensity of 100% A positively charged ion
fragmentation
A pattern of "flying apart' that molecular ions
base peak
free radical m/e mass s~ectrom molecular ion
radical cation
undergo A palticle with an unpaired electron
The ratio of mass to charge; usually the charge is +I so it is the mass of the particle The plotting of a series of peaks of varying intensity based on m/e A molecule that has been bombarded with a ~beam of elecrrons cads ng one e eclron lo be dislodge0 TnLs. .I has tevder e eclrons tnan protons and is positively charged ~
The students' excitement was obvious a s they anticipated the appearance of information on the computer screen. Several students were already familiar with comTable 2. Compounds for Student ldentification of Three Peaks in the Mass Spectrum
Comwund
Conceot from Key Peaks for Usefulness as course ldentification Teaching Tool Addressed benzoohenone aromatic loss of ring good ketone biphenyl
aromatic hydrocarbon
large molecular ion
naphthalene
aromatic patterns
ring fragments excellent
fumaric acid
cisitrans isomerism
loss of H z 0
fail
stearic acid
fatty acid of biological importance
aliphatic fragments
excellent
salicylic acid
starting material for aspirin synthesis
loss of H 2 0 loss Of C 0 2
good
cholesterol
typical steroid
loss of side chain
excellent
caffeine
loss of N-CH3 excellent heterocyclic compound miscellaneous purine structure ring fragments
good
~~~~~
A positively charged ion which has an unpaired
electron
Figure 2. Analysis of a 1 :I toluene-benzene mixture by combined gas chromatography and mass spectrometry
Volume 69 Number 1 January 1992
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Table 3: Student Participation and Evaluation
Spring 1988
Figure 3. Excerpt from student assignment exercise C. Compounds 3 and 4 are isomers with the formula C,H,,. Based on other tests, the possibilities have been narrowed to propylcyclobutane, ethylcyclopentane, or methylcyclohexane. Identifyeach. puters, b u t not with t h i s type of chemical application.Usine the comouter-stored data, the demonstrators graphically, k i t h coordinate adcould answer justment by the technician. For example, "What is the identity of the compound coming offthe GC a t 3 min 20 s? " The technician then switched to the mass spectrum display and continued the identification process. At t h e end of the tour, each student was given the spectrum of a compound that had some relevance to the course. Each student was given the spectra of eight different compounds that had been analyzed before the tour. The compounds' names, b u t not their formulas, were provided, as listed in Table 2. Part Ill:Completion of an Exercise and Identification of a Compound
Students were asked to complete a short exercise that was distributed with the handout. Typical questions were "Identify the compound" from the spectra ofwater and ammonia and "Distinguish the isomers" from the spectra of two wmpounds. (See Figure 3.) An interpretation of the spectrum obtained at the end of the tour (compounds i n Table 2) was completed by the identification of three peaks. As is frequently the case, more data was generated than could be analyzed. However, each spectrum contained features that were recognizable based on the material presented. Most students were surprised a t how easily they wuld identify the major peaks. I t was then apparent that a n experienced mass spectrometrist wuld become quite pmficient a t deducing structures. I t was also apparent that identifying a n unknown compound would be much more difficult. Overall Success of the Project The project was successful i n many ways. The enthusiasm and interest of the students was high, and they genuinely learned something about chemical analysis, a s well as developing an impression of life a s a professional scientist. The TA's also benefitted from the work. Evaluation of Student Interest and Performance
As summarized in Table 3, participation was extremely high. The tour attendance was 979XXsomewhat greater t h a n a typical lecture. Since half of t h e tours were
50
Journal of Chemical Education
Springa 1990
110 145 Number of Students Enrolled 55 major in health-related field major in technical field 60 miscellaneous 30 97% 96% Percent of Students Completing 3 Parts Percent Giving a ~avorable~ Ranking of 65% Project overall 71% major in health related field 30% 80% major in technical field 2% miscellaneous Percent Ginving an UnfavorableCRanking 5% to the Project overall 13% 15% major in health related field 5% major in technical field miscellaneous 5% 'During the spting of 1989. the instrument was being moved. b~ ranking of 7 on a scale of 1 (leastfavorable)to 10 (mostfavorable) 'A ranking of 1 on a scale of 1 (leastfavorable)to 10 (most favorable) scheduled for a Friday afkernoon, this showed support for the project. Offering quiz points probably had some bearing on the attendance (6) Exam grades showed that the students did learn some analytical chemistry from their experience. On one section of an hour exam related to mass spectrometry, the Spring 1988 students were asked to complete four short-answer questions. Thirty-three percent ofthe students were able to complete the questions with greater thatn 85%accuracy, while 68% scored greater than 75%. On a comparable exam administered during the Spring 1990 semester, t h e students were asked to sketch a spectrum of carbon tetrachloride, remembering to consider the natural isotooic abundances. which were eiven. Sixtv percent of the students were able'to complete tKe taskwitL meater than 80% accuracv. while 85% of the students completed the task with greater than 50% accuracy. Feedback From Students
Student comments were overwhelmingly positive. "I always wondered what the TA's did in their spare time." "I would like to see some of the other big gadgets around here." "I'm an engineer, and this appealed to me more than other topics in the course." "This should be done for parents' weekend." "It was interesting to see a real application of the theory."
We also found t h a t meeting with students in small groups in an unusual learning situation was a very positive exoerience. As anticioated. thosemaiorin~in technical disciplines were more enihusi&tic thanVthosemajoring in the health-related fields. as we learned from the one m - o u. ~ of students for whom we determined the relationship between major field and project interest. !See Table 3. The ProfessionalImage
The team approach to solving research problems was dynamically illustrated by t h e interaction among the course instructor, guest lecturer, graduate students, and technicians. Each person was introduced, and they all shared their personal backgrounds and career paths. Verbal reference to the other members of the team was fre-
quent. The multifaceted nature of chemistry was showcased. The graduate teaching assistants were able to present the material in a manner consistent with the aim of the project. The experience of discussing a research technique with introductory students was also deemed worthwhile for the TA's. I t appeared to enhance the image of the TA's in the students' eyes.
Department of Chemistry, Ohio University, is further acknowledged. This article is based in part on a paper presented a t the 21st Central Regional Meeting of the American Chemical Society, Cleveland, OH, June, 1989. Literature Cited 1. Crosby, G. A. J Chmn. Edvr 1989,66,& Smith, S. G.:Jones,L.J. Chrm Educ 1989, 66. 8. Lagowski, J. J. J. Chrm. Edue 1989.66, 12. Moore, J. W. 1999.66, 15.
Acknowledgment
I wish to thank K. F. McDaniel for presenting the guest lecture, and D. E. Zacherl, P. J. Tandler, and E. Saulinskas for assisting with the tours. The financial support of the
J Chem. E d v c
2. Kmiger. J. Chem. Ens. NGUE1989, (NOY271.54. 3. Beall. H; Berka,L.H. J Chmr Edue 1990.67. 103. 4. The WnrldofChambtry;Adlei I. Ben-2il.N.. Eds.:Saunders:Phlladelphia, 1989. 5. Steehler, J. K. J. Chvm Educ ISSO. 67, A37. Brown, T M.: Dmnrfield, A. T.; Ellis. R. J Chem Educ 1M", 67,518. Stah1.J. W. J. Chem. Educ 1990,67,A72. 6. Eiehstadt, K. E. J Chvnz. Educ. 1989. 66, 326.
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Number 1 January 1992
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