An Idea To Save Time and Money with Recording IR Spectrophotometers The advent of sophisicated Fl-IR instruments for research purposes has resulted in large numbers of older recording infared spectrophotometers (IR) being donated to teaching programs; thus the recording IR spectrophotometer is h e coming a familiar piece of instrumentation in the undergraduate laboratory. The older machines have some limitations and problems (they are slower and less accurate, less sensitive, and it is difficult ta recwer the sample). These problems would not exclude their use from an undergraduate lab class. Students from organic lab classes can use them to verify results from experiments, and Physical Chemistry lahs might deal with some theoretical aspect of infrared spectroscopy an a measurable physical system. Most laboratory instruction place considerable value on learning IR spectroscopy; following the idea presented here might save time and frustration for both the student and the person in charge of the lab. When the student places the sample in the IR insrtument and attempts ta get a n IR spectral profile of the compound, the pen frequently goes off scale a t 180&1600 cn-' and the run must be repeated aRer the IR instrument has been adjusted. The ideal peak for the strongest stretches should go approximately 90-95% full scale; if the student takes three complete cycles to get one usable lR trace, this is obviously a waste of paper, not to mention the cost of additional rolls of paper and the time that it will take the instructor ta replace the paper in the recorder. What we propose is fairly simple. Step 1:do a dummy run (leave the pen out of the recorder) and watch the pen holder, see if: a) the pen holder gaes off scale, orb) the pen holder goes less than 90% full scale. Step 2: Reverse the paper hack onto the spwl (check instrument manual) and adjust the parameters on the spectrophotometer to bring the peak maximum to 90% full scale. Step 3: do another dummy run to see if the parameters are properly set. Repeat step* 2 and 3 untd the pen holder stays within the optimal limiu. Once the correct setting has been found. reverse the chart paper and start the run again rvccpt this time use the pm in the rcrord~r'This procedure takes the same amount of time as i t would to generate a proper IR spectrum, minus the time taken ta rewind the chart paper (not long), and this method will prevent the waste of expensive paper.
1030
Journal of Chemical Education
