In the Laboratory edited by
Topics in Chemical Instrumentation
David Treichel
The Role of Automated Instrumentation in Undergraduate Chemistry
Nebraska Wesleyan University Lincoln, NE 68504
Suzanne Bell Department of Chemistry and Biochemistry, Eastern Washington University, Cheney, WA 99004-2431;
[email protected] Rationale Few would dispute the need to integrate modern instrumentation into the undergraduate chemistry curriculum. However, little attention has been paid to the incorporation of automated systems, which are the mainstay of many industrial and research laboratories. To address this, Eastern Washington University (EWU) acquired an automated gas chromatograph/mass spectrometer system equipped with an automatic sample injection system (autosampler) and a multisample purge-and-trap system (GC/MS/PT). Laboratory exercises and projects exploiting the system’s capabilities have been included in several courses. While the following discussions relate to this particular instrument, findings can be generalized to any multisample system such as autotitrators, spectrophotometers, and chromatographic systems. The need to make chemistry curricula applicable to the needs of employers is a continual concern (1–3). Chemists, particularly analytical chemists, increasingly rely on computerized instrumentation capable of unattended, multisample operation. Tasks such as calibration, quantitation, reporting, and sample dilution can be automated. Graduates entering the work force are faced with the challenge of adapting their academic experience to the reality of automated instrumentation. To adequately prepare students to enter a competitive job market, it is crucial that they be provided with the skills necessary to do so (4). However, industry often voices concerns about the dichotomy between the skills imparted to students and the needs of employers (5). Even traditional research laboratories are increasingly dependent on automated instruments (6 ); therefore the need to incorporate some aspect of their use into undergraduate education is a necessity rather than an option. Debate continues on how best to exploit instrumentation (7–10) and such discussions are relevant to automated instruments as well. Understandably, agreement exists that before using any instrument, students must have a firm grasp of chemical principles and some understanding of instrumental theory. Coupled with this is the need for computer and datainterpretation skills. While the depth of this background can vary depending on course level, experience with complex instrumentation is of little value if the instrumentation is treated as a “black box” (7). Automated instruments exacerbate this concern. Students must understand how and why an instrument works before it can be properly employed. Careful curricular planning can address this. As an example, consider the use of an autotitrator (11). In this case, students are afforded considerable experience with manual titrations before working with the automated system. Similar guidelines were followed in the work described here. Automated instrumentation is
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not a substitute for knowledge and laboratory technique. Rather, such systems demonstrate how this knowledge can be resourcefully exploited. Several advantages are offered by automated systems, the most obvious being efficiency. A single instrument is often insufficient to serve a large class (8). Typical autosamplers have sample capacities of 100 or more, and unattended operation allows students, TA’s, and instructors to spend valuable lab time in the lab rather than making manual injections. Since autosamplers typically support multiple methods and calibrations, several classes can utilize an instrument simultaneously. Finally, automated instrumentation facilitates the inclusion of quality assurance and quality control (QA/QC) into experiments with a reasonable time investment. Given the ubiquity of QA/QC in industrial, research, and government labs, this is a critical issue (3, 12). Replicates are easily accommodated to provide a measure of precision. Multiple injections of a single sample can vividly illustrate the magnitude of instrumental uncertainty compared to experimental uncertainties and errors. Unattended operation facilitates other QA/QC exercises, such as control charts, that require replicate daily analyses. Concepts such as continuing calibration, spiking, and fortification can be utilized as they are in commercial settings. Finally, students acquire an appreciation for the volume of data that is produced by automated systems. In turn, this promotes proficiency in data analysis, evaluation, and reporting—skills that reflect what will be expected of students in the workplace. As with any instrument system, there are limitations that must be acknowledged and addressed if the automated system is to be successfully integrated into the curriculum. One worry, particularly in the cash-strapped academic world, is that complex instrumentation creates high maintenance costs, particularly when used in introductory courses (8). On the basis of our experiences at EWU, this fear is overstated. Most automated instruments are designed for round-the-clock operation under the demanding conditions found in environmental or forensic laboratories. Manufacturers have invested considerable effort to minimize downtime even in the absence of a service contract. With a sound program of preventative maintenance, there is no reason why automated instruments cannot be reliably incorporated into undergraduate laboratories. The EWU system has enjoyed ca. 95% “up time”, demonstrating that complex instrumentation need not be prohibitively complex or expensive to maintain. Other studies have borne this observation out (8). A second concern is that even the best-designed instrumental experiments, automated or otherwise, involve only perfunctory experience with any individual system. This limitation can be addressed in a number of ways. At EWU,
Journal of Chemical Education • Vol. 77 No. 12 December 2000 • JChemEd.chem.wisc.edu
In the Laboratory
students commonly expand on instrumental experience by participating in undergraduate research and directed study activities as described below. It is in these arenas that cursory experience can mature into familiarity and expertise. However, this option is not available to or exercised by all students. A common alternative is to address general techniques that are refined using different but related analytical systems. For example, the broad topic of chromatography can be explored using gas, liquid, and ion chromatographs. Such experiments can and should span a variety of courses such as organic, quantitative analysis, and environmental chemistry. Automated instruments are particularly useful for reinforcing “core concepts” of quantitative and instrumental analysis such as representative sampling, use of replicates, blanks, proper calibration, and identification of suspicious results. Instruments, automated or otherwise, perform only as well as the operator; improper calibration will yield poor results with a sophisticated and expensive instrument just as surely as improper calibration will yield poor results on a SPEC-20. Since automated instruments facilitate multiple samples and batches, instructors can design experiments to specifically illustrate these core concepts without spending an inordinate amount of time or lab periods doing so. Finally, a few practical issues must be addressed. Replicates and multiple samples consume additional reagents and generate additional waste. This is not a trivial concern, given that many organic analyses require the use of solvents such as methylene chloride. More samples mean more preparation time. Thus, careful attention must be paid to the compromises involved, and microscale sample preparation options should be exercised whenever possible. The purge-and-trap system, because it analyzes water samples directly without extraction, has little impact on waste volume generated. Instrumental System The GC/MS/PT was purchased in 1995 with the help of an NSF Instrument and Laboratory Improvement (ILI) grant. Both conventional injections and purge-and-trap operations are multisample capable and automated, and relevant parameters are presented in the box. Purge-and-trap is a sample preconcentration system used for the analysis of volatile organics such as specified in Environmental Protection Agency (EPA) and other standard analytical methods. The sample matrix can be soil or water. The volatiles are removed via a helium purge that concentrates the volatiles on a trap. At the end of the purge cycle, the trap is rapidly heated and back-flushed with helium and deposited at the head of the capillary GC column. Purge-and-trap is extremely efficient and has the added advantage of eliminating solvent extraction. Integration into the Curriculum Two avenues have been used to integrate the instrument into the undergraduate curriculum: traditional laboratory exercises in the Quantitative Analysis and Environmental Chemistry courses, and directed-study classes, which encompass undergraduate research or community-service projects. Examples of each are presented below and references are provided for readers who desire experimental details.
Traditional Laboratory Exercises Not surprisingly, the most extensive use of the instrument has been in Quantitative Analysis. Purge-and-trap capabilities are used to determine the concentration of chloroform in swimming pool water using an EPA trihalomethane method (12). Students are provided with 40-mL amber vials and instructed on how to collect water samples from the campus swimming pool. Organic material in the pool reacts with the by-products of chlorinated disinfection agents to produce trihalomethanes, including chloroform at ca. 40 ppb. Using a standard EPA method, the samples are analyzed using GC/MS/PT. This experiment introduces students to EPA methods, the concepts of spiking samples, matrix effects, blanks, replicates, and data analysis, and to reporting that integrates QA/QC. The Environmental Chemistry course uses a similar procedure to study organic priority pollutants in water. Direct injection is used to evaluate simulated arson samples by minor modifications of existing methods (13, 14). Samples are prepared by filling a large crucible with combustible material such as newspaper, wood scraps (splints and toothpicks work well), or cotton. To this, ca. 2 drops of various accelerants such as different brands of gasoline, charcoal lighter fluid, kerosene, aviation gas, and jet fuel are added. Under close supervision, the sample is ignited in the hood and allowed to burn for a specified time or until exhaustion. For added realism, samples may be extinguished with water at various time intervals. A small portion of the burnt sample is transferred to a 1-mL autosampler vial, enough to fill it ca. 1⁄3 full. One milliliter of pentane is added, the mixture is agitated gently, and samples are stored in the refrigerator until analysis. Initially, 1 µL of the extract is injected using the specified instrumental criteria (see box) and the following oven temperature program: injector 260 °C; column 50 °C, hold 2 min, 12°/min ramp to 240°, hold 10 min. All these criteria can be modified as needed and sample dilution may be required on the basis of initial results, a valuable experience for students that reflects realistic complications faced by arson analysts.
Instrument Configuration Gas Chromatograph Hewlett-Packard (HP) 6890 Column: HP-624 25 m × 0.20 mm × 1.12 mm Electronic Pressure Control Mass Spectrometer HP 6890 Series MSD EI mode default; CI option Autosampler HP 6890 Series 100 sample capacity, tray cooling enabled Purge-and-Trap HP Purge-and-Trap Concentrator Trap: Supelco (Supelco Park, Bellefonte, PA) Vocarb trap HP Purge-and-Trap Autosampler (16 samples) with heaters Split Ratio/Flow Settings Purge and trap: 12:1, 0.8 mL/min constant flow Direct injection: 10:1, 0.5 mL/min constant flow Data System HP Vectra Pentium-90 with EnviroQuant software control
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The advantage of an autosampler in this laboratory exercise is that each student can run many samples obtained under different conditions. Factors that can be varied include the combustible material, accelerant, time of burning, use of water to extinguish, and weathering (allowing the burnt material to sit exposed for set periods of time). Like a real arson sample, the burnt material will not be homogeneous, as can be clearly illustrated by sampling and comparing different portions from the same crucible. Additionally, the automated capabilities of the instrument allow students to run replicates and spikes. Matrix effects are vividly emphasized and a direct connection to real-world chemistry is made. Although the applications and emphasis will be different, automated instrument systems can play a role in non-major and overview courses as well. Here, automated instruments can be used for demonstration and illustration as opposed to the more in-depth approach demanded in courses for science majors. As an example, the arson laboratory discussed above could be used effectively because most students are familiar with and interested in forensic science. For this module, lecture material could use the subject of arson to frame a discussion of combustion, sampling (selection, collection, and storage), analysis, and interpretation. Since such students are not majors and are not intending to work as practicing chemists, a cursory discussion of the instrument and function is adequate. Chromatographic separation can be illustrated using a simple demonstration of inks separated by thin layer chromatography. Mass spectrometry can be similarly explained in terms of fragmenting molecules in recognizable and reproducible pieces. The arson lab can then be modified to concentrate on the different chromatographic patterns of gasoline, diesel, and charcoal lighter fluid. The autosampler would allow each student to run several samples and to explore the effects of such variables as water, burn time, and weathering on the chromatogram.
Directed Study and Capstones At EWU, juniors and seniors participate in undergraduate research or independent study by enrolling in directed study courses or the senior capstone experience. Many students, having been exposed to GC/MS in Quantitative Analysis, Environmental Chemistry, or Organic Chemistry, take advantage of this opportunity to obtain additional experience on the automated system. The direct injection autosampler has been used to study flavorings in candy and to develop the arson laboratory described above. However, projects incorporating the purge-and-trap technique have proved the most popular. In directed study, students first tackle a system tutorial. This is followed by background studies in mass spectrometry and chromatography. They then pursue a task of interest to them and of service to the department or the community. A recent project involved the analysis of water from the local wastewater treatment plant. The plant uses an innovative
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wetlands tertiary treatment and students tested the influent and effluent from the wetlands for the presence of volatile organics. Sampling considerations, storage, holding time, matrix effects, and QA/QC concepts were addressed and enforced, and one student went on to work at a local environmental laboratory as a result of the experience obtained. Other students have examined local wells and campus water supplies. A current project is a cooperative venture with local government involving analysis of water supplied for the presence of methyl-tert-butyl ether (MTBE). MTBE is used to oxygenate gasoline and has become an environmental concern as a drinking water contaminant. The real-world connection and sense of service provided makes this an ideal project for advanced students. Conclusions With proper planning, both logistical and curricular, complex automated instruments can be successfully integrated into undergraduate chemistry programs. The greatest challenge is balancing the advantages of black boxes, such as speed, convenience, and capacity, with the disadvantages. Automated instruments cannot be considered a substitute for chemical or instrumental knowledge but rather a supplement to both, necessitated by the changing way in which analytical chemistry is practiced outside of academia. Acknowledgment I gratefully acknowledge the support of the National Science Foundation through the ILI grant program (9591724). Literature Cited 1. Bayer, R.; Hudson, B.; Schneider, J. J. Chem. Educ. 1993, 70, 323. 2. Fanning, J. C.; Fanning, S. S. J. Chem. Educ. 1993, 70, 563. 3. Perone, S. P.; Pesek, J.; Stone, C.; Englert, P. J. Chem. Educ. 1998, 75, 1444. 4. Lagowski, J. J. J. Chem. Educ. 1998, 75, 425. 5. Mabrouk, P. A. J. Chem. Educ. 1998, 75, 527. 6. Tolman, C. A.; Parshall, G. W. J. Chem. Educ. 1999, 76, 177. 7. Jones, B. T. J. Chem. Educ. 1992, 69, A268. 8. Steehler, J. K. J. Chem. Educ. 1998, 75, 274. 9. Christian, G. D. Anal. Chem. 1995, 67, 532A. 10. Eichstadt, K. E. J. Chem. Educ. 1992, 69, 49. 11. Williams, K. R. J. Chem. Educ. 1998, 75, 1133. 12. Bell, S. C.; Moore, J. J. Chem. Educ. 1998, 75, 874. 13. Elderd, D. M.; Kildahl, N. K.; Berka, L. H. J. Chem. Educ. 1996, 73, 675. 14. Keto, R. O.; Wineman, P. L. Anal. Chem. 1991, 63, 1964.
Journal of Chemical Education • Vol. 77 No. 12 December 2000 • JChemEd.chem.wisc.edu
