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IR Spectroscopy of Liquids

Liquid organic compounds can be examined directly as a thin film, "neat", between two NaCl plates. By "liquid organic compound" we mean pure organic compounds that are liquids at room temperature, not solutions of a solid organic compound in a solvent. Although it is possible to run a solution as a thin film between two plates, the resultant spectrum would show bands of both the compound of interest and the solvent.

Obtain two salt plates from the desiccator in the main fume hood in your lab. Ideally, the plates will already be clean. If necessary, clean the plates with a small amount of acetone. The plates should also be transparent, but quite foggy plates usually give acceptable spectra.
Use a Pasteur pipet to place a drop of your liquid unknown on one salt plate.
Put the second salt plate on top so that the liquid spreads into a thin film. When running a liquid sample, you need to have two plates, both to prevent the liquid from running off the plate and to prevent it from evaporating.
Pick up the plates and take them to the IR. Carry them by the edges and/or wear gloves. (Gloves are advised because sometimes the liquid compound leaks out from between the plates.)
Take the plates to one of the FT-IR instruments and place them in the V-shaped sample holder inside the instrument. Obtain the IR spectrum. Once you have obtained your spectrum, clean the salt plates again with acetone and return them to the desiccator.

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