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Enhanced Chemiluminescence

May 18, 2013

My Physical Chemistry II lab session this semester (Spring 2013) gave me ample occasion to introduce students to my own field of spectroscopy, which was truly a joy. Experiments gave students exposure to absorbance, fluorescence, and chemiluminescence, and (if I am successful in reviving some donated equipment) I plan to include Raman spectroscopy in years to come. Chemiluminescence and fluorescence are particularly important topics of study as many students will likely find themselves working in biotech, and these are key spectroscopies in bioanalytical and clinical work.

Even in teaching other venerable "P-Chem" topics, I leaned toward lab methods that were based on spectroscopy where possible. Of course, our kinetics labs included fluorogenic and chemiluminescent reactions. And naturally, at the conclusion of any lab session working with chemiluminescence it would be a shame to just dispose of one's unused reactants by just dumping them, unreacted, into the waste container. Surely even the most jaded lab denizen cannot resist a "grand finale".

Here my students indulge in just that, adding peroxide to their carbonate-buffered stock solution containing 1mM luminol, horseradish peroxidase, and enhancer. Light is emitted at about 440nm as an unstable T1 excited state, produced by reaction of oxygen with the luminol dianion, undergoes intersystem crossing to an S1 excited state that subsequently decays radiatively. Bubbles of oxygen gas from the peroxide/HRP reaction are seen at the surface of the mixture. The second "pour" shown is the student adding additional H2O2 in hopes of another burst of light, but alas, the luminol was spent at that point.

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