Sunday, September 28, 2008

ATR Arrives in FTIR Lab

Long before I began teaching the undergrad orgo labs full-time, I was a TA for this course when I was a chemistry graduate student at UIC. At the time, there were few analytical techniques available for the characterization of organic molecules: no melting point apparatuses, no IR, no TLC and a sporadically functional GC with an unbearably slow analog plotter. A typical synthesis lab was often concluded by the students proudly shoving a yellow powder at me exclaiming, “See, I did it.” Sadly, I would acknowledge their accomplishment with a solemn nod, after which they would chuck their powder into the waste container with a strange jubilation. What was the point, I wondered. That yellow powder could have been anything. After about three years as a teaching assistant for this course, I was shocked one day when I found an infrared spectrometer in what is now the instrument room. I couldn’t believe we weren’t using this equipment in our labs. When I was hired as the full-time instructor, I made utilizing the IR my first priority.  Of course, I quickly realized why this technique had been left by the wayside for such a large class: time. Time training TA’s and students, time creating instructional handouts, and time maintaining the spectrometer were all factors, but the time that it took students to acquire a decent spectrum was the most formidable challenge of all—primarily because of the difficulty students had with sample preparation. For liquid samples, students sandwiched a thin film between two NaCl plates. After the tenth plate was ruined by accidentally washing with and thereby dissolving in water, we switched to disposable PTFE cards. These worked well enough, but it was difficult to get spectra of volatile samples.

Solid samples had to be ground with anhydrous KBr and pressed with a die into a transparent disc. While seemingly straightforward, a number of conditions had to be met precisely right in order to obtain a disc of sufficient transparency and with a high enough sample concentration to acquire a spectrum in less than 5 minutes. The tension was palpable during these labs, especially when time was running short and the line for the IR wound outside the instrument room like a snake threatening to choke the sanity out of student and TA alike.

I’m happy to say, those days are over. The attenuated total reflectance (ATR) accessory, which I have fought to acquire since I began teaching this course, has arrived thanks to the differential tuition money that was made available to the Chemistry Department this year. After several tedious hours of tuning, aligning and swearing, the Pike Technologies GLADiATR was successfully installed. Then came the time of reckoning. After acquiring 64 background scans, I nervously applied a small amount of solid acetanilide to the 2 mm2 diamond crystal, lowered the pressure clamp and then turned the clamp dial clockwise until the pressure tip had pressed the solid into the diamond at 40 pounds of force. I clicked the scan icon on the screen and one minute later I was looking at my first successful ATR spectrum. The results were amazing. The total acquisition time from start to print was 3 minutes—a far cry from the 20 minute average for the KBr technique. Could it really be this easy? After twenty or so spectra later, the answer was a resounding yes. I was ecstatic. It’s a great feeling to know that this technology will radically change how IR is approached in CHEM 233 and I am anxiously awaiting to see how it will be received by the CHEM 233 students this semester.
Please click here for a full-color version of the instructions for using the GLADiATR accessory.

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