8 . HATR Sampling Accessory User’s Guide
Choosing the top plate
The HATR can be used to analyze powders, pastes, gels and liquids using a trough top plate,
where the sample is poured into the trough. Alternatively, a flat plate may be used for
homogenous solid samples, solid surfaces, or coatings on solid samples. Force may be
applied to ensure good contact between the sample and the crystal. The flat plate can also
be used to analyze gels and pastes, by spreading them on the surface of the plate.
The HATR can be supplied with top plates fitted with zinc selenide (ZnSe), germanium (Ge)
or AMTIR-1 crystals. Consult your PerkinElmer Sales Representative for further information
about available top plates.
Choosing the correct crystal
Zinc selenide (ZnSe) crystals are most commonly used as they have a wide range
(650–17000 cm
−1
) and a refractive index of 2.4. However, zinc selenide is incompatible with
many acids and bases. Therefore AMTIR-1 is often used as its properties are very similar, but
it is more resistant to acids.
Germanium (Ge) crystals have a high refractive index of 4.0 and are used for highly
absorbing samples such as carbon-filled polymers and rubbers, and samples with a high
water content. These crystals are also resistant to strong acids and bases.
NOTE: Derivative shaped bands can be observed in the spectrum if the refractive index of
the sample is too close to the refractive index of the crystal. For this reason,
alternative crystal types may be required for specific sample types. Consult your
PerkinElmer Sales Representative for advice.
Details of the top plate crystal are displayed in Spectrum software, and this information is
stored in the status information for each spectrum collected.
Figure 3 Top plate details displayed on the Setup Instrument Basic tab in
Spectrum software
Please ensure that you have read the safety information starting on page 4 of this User’s
Guide for your crystal type before continuing.
Choosing the angle of the crystal face
The number of internal reflections and depth of penetration of the beam can be decreased
and absorbance bands in the spectrum weakened by using, for instance, a 60° crystal rather
than a 45° crystal.
