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Keith A. Oberg and Daniel R. Palleros[1]
Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064
Infrared spectroscopy (IR) is one of the most ubiquitous techniques used in the introductory organic chemistry laboratory. This is true, in part, due to the simplicity of the method and the availability of instrumentation. Despite this, some mishaps are unavoidable in classes with a large number of students. One of the most common casualties when running IR spectra are the sodium chloride windows used as sample support. Even with proper care these plates require frequent polishing, they wear out, and eventually must be replaced. In our experience, in a class of over 200 students, each of whom collects at least six IR spectra over a 10-week period, 15 pairs of windows typically have to be replaced. This amounts to over $300 a quarter. Given the calamitous budgetary situation in the state a California, we set out to find a less wasteful way of obtaining IR spectra.
Any alternative to NaCl plates should be transparent in the IR region to be analyzed, simple to use, and give reproducible results. In addition, the support should have minimum scattering of IR light. There has been an early report (1) on the use of Teflon tape as an IR window material. Recently, disposable sample cards made of microporous polytetrafluoroethylene (PTFE, Teflon)[2] and polyethylene have become available commercially. They consist of a polymer film secured on a piece of cardboard with a round hole in the center. These cards provide a fast and clean method to run IR spectra. Unfortunately, the cost of using them ($1.80 each) in a class of about 200 students would be about $2000 a quarter, six times more than our expenditure in NaCl windows. Therefore, we set off to make similar cards using Teflon tape available in most hardware stores for only $2.50 per 100-ft roll (enough for an entire quarter of IR spectra). We found that the homemade cards give IR spectra as good as those obtained with NaCl windows, provided certain precautions are taken in their preparation. In this paper we describe a quick and reproducible way to make Teflon IR-cards and to obtain good quality spectra using them.
Our first attempt at making...