In the Laboratory
Juicing the Juice: A Laboratory-Based Case Study for an Instrumental Analytical Chemistry Course Peter M. Schaber,* Frank J. Dinan, Michael St. Phillips, and Renee Larson Department of Chemistry and Biochemistry, Canisius College, Buffalo, New York 14208, United States *
[email protected] Harvey A. Pines and Judith E. Larkin Department of Psychology, Canisius College, Buffalo, New York 14208, United States
A variety of nontraditional instructional approaches have been described in recent times. Peer-led instruction (1), problembased instruction (2), guided-inquiry learning (3), team learning (4), and case-study teaching (5) are examples of these innovative pedagogies. Case-study teaching has proved successful at this institution (6-8) and elsewhere (9-14). Case-based laboratories are a variation on case-study teaching and offer students a better approximation of real science than conventional undergraduate laboratory experiments. The laboratories are based upon real-world stories that involve characters students can identify with and ask students to deal with problems that challenge their creativity in ways that conventional “cookbook” laboratory experiments do not. Case-based experiments should, to the extent possible, require students to develop their own plan for dealing with the problem(s) posed by the case and to critically assess and apply their experimental data. Case-based experiments should also require students to write a narrative report explaining how their data were obtained and applied, the significance of their results, and how their results answer or fail to answer the problem(s) associated with the case. A well-designed laboratory-based case study should tell a story that the student audience can identify with and that has an experimental solution. It should require student teamwork and involve minimal faculty guidance. Good cases should be brief and structured in a manner that allows student to develop a feeling of ownership for the experimental approach that they design. The instructor's role should, ideally, focus on answering student questions and assessing the safety and effectiveness of the experimental procedures that the student teams propose to deal with the case's problem(s). Safety is of primary importance and must be stressed when evaluating the experimental plan the students develop to attack the case. The “Juicing the Juice” case study requires small teams of students to conduct themselves as chemists would in the “real world”. The laboratory instructor provides students with the case study 1 week prior to the laboratory. The student teams must develop their own experimental approach to the problem posed in the case. During a 1-h prelaboratory session, the instructor provides a general overview of the case, emphasizes safety issues, answers questions, and begins the process of reviewing team approach plans. The approach plan must meet with the approval of the instructor before a team is allowed to begin the experiment. Student teams then collect appropriate quantitative data and interpret and apply those data. In the process, students are exposed to the use of an inductively coupled plasma (ICP) spectrometer, application of least-squares analysis to the data 496
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collected, data interpretation, the application of statistical analysis to determine whether samples significantly differ, and the writing of a narrative report based on their analysis. The Case Study This laboratory-based case study was suggested by an actual problem that a regional Food and Drug Administration (FDA) laboratory was called to investigate. A supplier of “fresh-squeezed orange juice, not from concentrate” approached the FDA laboratory claiming that a local orange juice supplier was underselling his product by reconstituting cheaper “orange juice concentrate” using local municipal tap water and selling it as “fresh-squeezed orange juice, not from concentrate”. Orange juice concentrate normally sells for a lower price than the fresh-squeezed orange juice, and the complainant argued that the improperly labeled reconstituted juice was being sold at a higher price than concentrated juice normally sold for, but significantly less than the price charged for authentic fresh-squeezed orange juice. To investigate this improper labeling claim, the FDA laboratory had to devise procedures that could distinguish between the squeezed and reconstituted orange juice samples. That is the same challenge the student teams face in this case study. Squeezed orange juice has significantly different calcium and magnesium concentrations than orange juice concentrate that has been reconstituted using municipal tap water. The reason for this difference is that municipal tap water is associated with characteristic levels of calcium and magnesium ions (collectively contributing to total “water hardness”) that are location specific and at levels substantially higher than those commonly found in squeezed orange juice. This difference allows the reconstituted and squeezed juices to be identified. ICP spectroscopy (15) is used to measure the calcium and magnesium concentrations of each sample and to determine whether these measurements more closely correspond to that of authentic squeezed orange juice or to that of orange juice that has been reconstituted using local municipal tap water. An FDA supervisor explains to a young, newly hired chemist that an analytical method needs to be developed to distinguish between fresh and reconstituted orange juice and suggests that ICP spectroscopy be used. It should be noted that, although ICP instrumentation is used in the version of the laboratory described herein, this case study is also easily adapted to use with more commonly available atomic absorption spectroscopy (AAS) instrumentation as well (16) (see the supporting information for further suggestions).
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In the Laboratory
Student Action Juicing the Juice is designed for use in an advanced instrumental analytical chemistry laboratory course. Two or three person student teams work cooperatively to plan a procedure that utilizes ICP instrumentation to determine whether the unknown orange juice sample they will be given is reconstituted or squeezed. When their plan is complete, the student team presents it to the laboratory instructor who considers any possible safety problems that might arise, comments on any questionable aspects of the plan, and either approves it or asks that it be revised. After obtaining the instructor's approval, the teams are provided with 1000 ppm calcium and magnesium standard solutions (preserved in 2% nitric acid), their unknown sample (which may be either squeezed or reconstituted juice), a sample of authentic squeezed orange juice, a sample of orange juice reconstituted form local tap water, and a sample of local tap water. Student teams are then free to begin their experimental work. The teams are required to plot and conduct a least-squares analysis of their data, and calculate the calcium and magnesium ion concentrations in all of the samples. They determine at the 95% confidence level whether the orange juice samples significantly differ in the concentration of these ions. They are then required to write a report that explains their experimental procedure, lists the data they have obtained, and indicates the manner in which these data were analyzed. Hazards Caution and care should be exercised when using concentrated nitric acid and when diluting Ca and Mg standards (preserved with nitric acid). Nitric acid is corrosive and an oxidizer and even dilute solutions of the acid can cause skin and eye irritation. Gloves and safety goggles must be worn at all times when dealing with nitric acid or its solutions and any spills cleaned up immediately. It is advisable to perform manipulations with these solutions in a fume hood whenever possible. A centrifuge is used in this experiment and students need to be reminded not to attempt to remove any vials from the turnstile until the centrifuge has come to a complete stop. Standard safety precautions should be exercised with respect to the pressurized Ar gas used with the ICP instrumentation. All waste should be disposed of in an appropriate manner. Results and Discussion The advanced instrumental analytical laboratory course, populated largely by upper-level chemistry and biochemistry majors, is run in an “open” fashion where each student team signs up for a 4-h time slot once per week. This time slot is usually used for sample preparation and instrumentation time. Typically, a 1-h in-class introduction (prelaboratory) to the experiment is followed by a 3-h demonstration and instrumentation check-out session. For this case study, the students have had previous experience using ICP in an introductory-level experiment. (Some students were additionally exposed to ICP instrumentation in an introductory-level analytical chemistry course.) In the introductory experiment, student teams determined the Pb ion concentration in tap water, which exposed them to the operational procedures for using the ICP. This provided the basic skills needed to successfully complete this laboratorybased case study. All student teams were able to complete the
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preparation and analysis portion of this laboratory in a single 4-h weekly session. In a large majority of cases (>95%), student teams were able to properly identify their unknown sample. However, another goal when using laboratory-based cases is to have the students create a report that is complete, of high quality, and “professional” in its appearance. If this goal is not attained, the report is not graded, but returned to the students to be rewritten with the comment that, “your supervisor is not happy with your report for the following reasons...”. A 10% grade deduction is assessed under these conditions. Conclusion In laboratory-based case-study teaching, students respond to an experimental problem that is placed in the context of a story. The intent of this teaching style is threefold: to generate more interest and enthusiasm than would result if the same material were presented in a conventional academic manner; to avoid the “cookbook” approach that is, unfortunately, often the basis for undergraduate laboratory experiments; and to give students a feeling for how the material that they are learning can be applied in a real-world context. The experimental procedures developed by student teams, working collaboratively and receiving minimal guidance from their instructor, leads to correct identification of the unknown sample a large majority of the time. The assessment data indicate that, overall, the Juicing the Juice laboratory-based case study elicited extremely positive reactions from the students, especially with respect to their interest in and understanding of chemistry. The case-study approach also appeared to have an exceptionally positive effect on student interactions. An important goal of the advanced instrumental analytical chemistry laboratory was for students to work as independently as possible in the laboratory. Most of the students enjoyed working on this case study without the close supervision of the instructor. They perceived themselves to be working independently as chemists do in the real world. A large majority of students gained confidence in their ability to use the laboratory equipment in the future as research investigators. They felt responsible for operating the laboratory instrument and collecting the data properly. One of the laboratory course objectives is “increased student responsibility for instrumentation operation and data collection”. When asked if this objective was achieved, a large majority of students responded in a positive fashion. However, previous experience did increase the students' sense of self-efficacy when working with ICP instrumentation. Acknowledgment We would like to thank the National Science Foundation (DUE ILI-IP) 9650804 and (DUE CCLI-AI) 0410257 and the Canisius Earning Excellence Program (CEEP) for their generous support of this project. Literature Cited
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1. Sarquis, J. L.; Dixon, L. J.; Gosser, D. K.; Kampmeier, J. A.; Strosak, V. S.; Varma-Nelson, P. The Workshop Project: Peer-Led Team Learning in Chemistry. In Student Assisted Teaching: A Guide to Faculty Student Teamwork; Miller, J. E., Groccia, J. E., Miller, M. S., Eds.; Anker Publishing Co.: Bolton, MA, 2001; pp 150-155. 2. The Power of Problem Based Learning: A Practical `How To' for Teaching Courses in Any Discipline; Duch, B., Groh, S., Allen, D. E., Eds.; Stylus: Sterling, VA, 2001.
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14. Fortier, G. M. J. Coll. Sci. Teach. 2000, 30, 92–95. 15. Skoog, D. A.; Holler, F. J.; Crouch, S. R. Principles of Instrumental Analysis, 6th ed.; Thomson Higher Education: Belmont, CA, 2007; pp 254-269. 16. Skoog, D. A.; Holler, F. J.; Crouch, S. R. Principles of Instrumental Analysis, 6th ed.; Thomson Higher Education: Belmont, CA, 2007; pp 237-249.
Supporting Information Available The complete laboratory-based case study includes written directions used by the students; instructor notes containing detailed experimental procedure guidelines; sample student data and example calculations; CAS registry numbers for chemicals used, along with assessment instruments; summary and complete details and analysis of survey results. This material is available via the Internet at http://pubs. acs.org.
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