In the Laboratory
A Cost-Effective Way To Extend an Instrument's Life Suzanne Carpenter* and William Baird Department of Chemistry and Physics, Armstrong Atlantic State University, Savannah, Georgia 31419-1995 *
[email protected] Extending the usefulness of the instruments we have has never been more important. The current economic crisis has prompted all of us to re-examine how money is spent and to try to minimize our expenditures because of future uncertainties. Already the economy has affected the replacement of equipment (1), and at least in academia, “there is little flab left to cut” (2). Simultaneously, we are encouraged to be more “green”, which, in its encouragement of minimizing electronic waste, should prompt less abandonment of instrumentation that is still usable and relevant. We have been able to breathe new life into an aging 60 MHz NMR spectrometer used by hundreds of undergraduates each year in the second-year organic chemistry sequence. In addition to extending the instrument's life, the updated look of the instrument may positively affect student attitudes about its usefulness (3). A department value at this university is that students should use instruments to collect their own data as early and as often as possible in the chemistry curriculum. For this reason, the 60 MHz spectrometer was obtained nearly 20 years ago through the (obsolete) NSFILI program. It is used entirely by second-year students and we estimate that thousands of students have used it; each student using it half a dozen times over the two-semester lab sequence. Having said this, no doubt minor repairs have been necessary over the years, but we hit a seemingly insurmountable obstacle about a year ago when the plotter that came with the Hitachi model 1200 rapid-scan correlation instrument became nonfunctional. The high level of “student traffic” coupled with the minimal chemical maturity of those students precluded simply switching to using the JEOL 300 MHz instrument also available in our department. We were at a crossroads: Do we abandon our commitment to early and frequent student use of instrumentation or do we find a way to keep the old 60 MHz machine going? We chose the latter and would like to share how we modernized our instrument and have successfully extended the already long life of this workhorse NMR. Solution The attached plotter received output in the form of Hewlett-Packard graphics language, and we were unable to find an affordable printer to serve as a replacement. Software solutions were also cost-prohibitive. Because our NMR also has an oscilloscope display, we realized that we could tap into that feature and read the voltages controlling the x and y positions of the beam. We estimated that we would require a two-channel data acquisition (DAQ) device with a sample rate of several kHz or more. Our upper-level physics laboratories have used National Instruments USB-600x DAQ modules for some time, so our familiarity with them suggested we employ a USB-6009 (approximately $250). The USB-6009 is shipped with several 1266
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simple programs suitable for use in a variety of programming languages. One of these is used to gather data from both channels at 5000 Hz for 2 s, requiring user input only to choose a file name and start the acquisition. The data gathered is saved as a comma-delimited text file, and an Excel spreadsheet is opened for analysis of the data. The use of Excel's built-in Visual Basic for Applications programming language allows the process of importing, scaling, and plotting the data to be greatly simplified for the student. The student clicks a button to import a data file and then uses two slider controls to set the boundaries of the scan (necessary because the fixed-time data acquisition does not exactly coincide with a single sweep of the oscilloscope beam). Another button plots the spectrum and presents the student with a large movable red dot positioned with another slider control. The student moves this to the general area of the 0 ppm peak and presses another button, which then finds the location of the highest peak in that area. When the student accepts the spreadsheet's suggestion for the 0 ppm peak (or chooses to repeat the process, should the spreadsheet have chosen the wrong peak), another large red dot appears and a fourth slider control is used to position it somewhere in the “flat” part of the spectrum. When this point is found, the spreadsheet calculates and plots the integrated spectrum on the same graph as the original spectrum. The vertical position of the integrated spectrum can also be adjusted via a slider control. In practice, the entire process of data collection and processing can be completed in about 1 min. At this point, the student can save the entire spreadsheet (data and spectra) to a thumb drive and analyze it further (if necessary) on any PC, freeing the NMR for the next student. Using the Hitachi plotter, each student required 10 min to obtain a spectrum; thus, the new setup represents a more efficient use of the instrument and the instructor's supervisory time. The spreadsheet interface could certainly be improved, further automating the process. This would make a nice miniproject for a chemistry or physics student with even modest programming ability. Summary It makes good economic and moral sense to use what you have for as long as possible. The upgrade we made was inexpensive and could be accomplished by an upper-level physics or engineering student. It may be that, at some institutions, the instructional decisions are different and there is no need to resuscitate a 60 MHz NMR but the point is broader than that one instrument. The wise use of resources (electronic and personnel like the expertise of physics or perhaps engineering colleagues) can result in favorable fiscal and environmentally conscious decisions.
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Vol. 87 No. 11 November 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed100277m Published on Web 08/26/2010
In the Laboratory
Literature Cited
Supporting Information Available
1. Borman, S. A. Chem. Eng. News 2009, 87, 35–38. 2. Schrecker, E. Chron. High. Educ. 2009, 55, 31. 3. Miller, L. S.; Nakhleh, M. B.; Nash, J. J.; Meyer, J. A. J. Chem. Educ. 2004, 81, 1801–1808.
A parts list (with approximate costs); a photograph of the instrument setup; step-by-step screen shots documenting the recording of the proton NMR spectrum of ethylbenzene. This material is available via the Internet at http://pubs.acs.org.
r 2010 American Chemical Society and Division of Chemical Education, Inc.
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