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60 . Spotlight 200 User's Guide
2. Run a razor blade or the roller knife along the edge of the upper slide.
The triangular piece of the sample is sliced off, giving a wedge-shaped sample.
3. To mount the sample, rotate it so that it is positioned as shown on the right in
Figure 17.
4. Position it under the microscope so that the infrared beam goes through the thin end of
the wedge (circled in Figure 17).
Microtoming
A microtome enables you to slice a sample into thin cross-sections, 0.5 to 20 µm thick. It is
commonly used to prepare samples for light microscopy; the same range of thicknesses is
also appropriate for infrared microspectroscopy.
If you are trying to identify the individual components of a laminate, microtomed samples
give the best results.
Samples are often embedded in a supporting medium before they are microtomed. If you
must use an embedding material, choose it carefully so that it does not alter the sample by
reacting with it, dissolving it, or contaminating it. Some commonly used materials are:
paraffin wax: This is the preferred medium for infrared spectroscopy. It produces few
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spectral interferences, and it can usually be easily removed from the sample with warm
xylene.
β-pinene wax: This material is similar to paraffin.
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plastic embedding materials: These can be used depending on the size and porosity
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of the sample.
acrylic and epoxy resins: Although these are commonly used in light microscopy,
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they are not recommended for infrared, because they are hard to remove and can
cause spectral interferences.
Polymers
Pressing or squeezing enables you to reduce the pathlength of polymer samples such as
paint chips, thick films, elastomers, or fibers.
Diamond anvil cell
The miniature diamond anvil cell, shown in Figure 18, enables you to press polymers (or
other compressible samples). It enables you to both thin the sample and collect its spectrum
in the same device; this is an advantage when you have limited material available. It is small
enough to be easy to manipulate, and fits in the recessed retainer in the support for large
samples. By collecting a background spectrum of an empty area of the cell, you can
completely compensate for the absorption bands of the diamonds.
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