Analog Spectrophotometers in the Digital Age: Data Acquisition on a Budget

294 Journal of Chemical Education • Vol. 82 No. 2 February 2005 • www.JCE.DivCHED.org It is scarcely possible to go into a modern laboratory and not find computers hard at work. Computer data processing enables us to perform numerous helpful operations otherwise practically impossible: baseline correction, digital differentiation and integration, convolution, to name a few (1–3). Acquiring data from instrumentation, archiving the recorded spectra, and preparation of reports using appropriate software are common laboratory tasks. There are numerous new UV–vis and IR (mostly FTIR) spectrophotometers of high and intermediate levels of resolution that can easily perform the above-mentioned operations. Significant cost of such systems often prevents them from appearing in the undergraduate laboratory. On the other hand, low resolution systems (1–5 nm for UV and 10 cm 1 for IR), which are still expensive, often cannot provide enough resolution for some interesting laboratory experiments. At the same time older models of scanning UV–vis and IR instruments can show good resolution, stability, and accuracy, thus performing better than some newer computerized systems. Usually the older models are able to record a spectral area of interest in several minutes. This is compatible with the time necessary for sample preparation and data processing. The limiting step is the conversion of the analog output signal coming from such an instrument into a digital format. Considerable cost of high performance analog-todigital converters greatly limits their use for upgrading the old instrumentation. Certainly, the instructor can build a homemade data logger. For example, a simple design including an educational Stamp 2 microprocessor and a 12-bit analog-to-digital converter is described in detail in (4, 5). The use of a Visual Basic program and a 14-bit data acquisition card to interface scientific instruments to a personal computer were demonstrated in ref 6. An even simpler solution is to use an off-the-shelf device. Two types of 12-bit data loggers, LabPro (Vernier Inc.) and digital multimeters with an RS-232 interface, are commercially available. LabPro is widely used in high school and undergraduate laboratories (7). Some analog spectrophotometers, such as a Spectronic 20, can be connected to the computer through the LabPro computer interface. Digital multimeters are common maintenance tools in the instrumental laboratory. The interfacing of Metex model M4650CR and Radio Shack model 22-168 multimeters to personal computers and to an Apple Newton PDA handheld computer was described in ref 8. A Lego spectrophotometer interfaced to a digital multimeter was recommended in ref 9. The use of a data logger in conjunction with an oxygen electrode to monitor the generation of oxygen in photosynthesis was demonstrated in ref 10. In this article we would like to share our experience with interfacing various spectrometers with analog output to a personal computer running Microsoft Excel in the Windows environment.1