Infrared spectra are acquired using either the Nicolet 730 spectrometer or the Nicolet Nicplan IR microscope.

On the microscope, spectra can be acquired from areas as small as about 20 microns across, in transmitted light or reflected light mode.  Samples can be presented as self-supporting films, or as solids or liquids placed on a KBr disc.

With the spectrometer, solids can be examined, by transmitted light, as a dispersion in pressed KBr (the KBr disc), as a self-supporting film, or by Attenuated Total Reflectance (ATR).

For ATR, the sample (usually a film) is placed in contact with a prism made of a material of high refractive index.  As the IR beam passes through the prism, total internal reflection (TIR) occurs at each reflection from the sides.  However, there is sufficient penetration into the sample, assuming good physical contact, at each reflection for structural information to be acquired.  With this technique, the sampling depth depends on the wavelength of the light, and so varies across the spectrum.

There are two main materials from which the prisms are made.

(a) Thallium bromide iodide (KRS-5).  With this material, the sampling depth varies from about 3 microns to 15 microns across the spectrum.

(b) Germanium.  The sampling depth is about one tenth of that of KRS-5, i.e. from about 0.3 microns to 1.5 microns.  It is thus more surface specific, but requires much better physical contact between the sample and the prism, or the spectrum will be unacceptably weak and noisy.