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Preparing a Thin Film IR Sample
The IR spectra of liquids are conveniently recorded as thin films pressed between two salt plates. The resulting IR spectrum is exclusively that of the sample compound. The IR spectrum of Nujol oil is an example of the thin film method.
- Place one or two drops of the anhydrous liquid sample in the center of the KCl plate with a disposable pipet.
- do not let the pipet tip touch or scratch the plate
- tip: if you dip just the tip of a Pasteur pipet in the liquid sample and then touch it to the plate, surface tension should deliver just enough liquid to make a nice, thin film
- Place the second plate over the sample and, if necessary, gently turn the top plate to spread the sample.
- Place the "sandwich" of IR plates in the sample cell mount.
- Gently press and twist on the cover that holds the plates together.
- air bubbles should not be visible when the plates are held together
- Record the background.
- Record the spectrum.
- Clean up.
A Few Practical Problems to Watch For
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