6 . Universal ATR Sampling Accessory User’s Guide
How the UATR works
The technique involves placing a sample on top of a crystal with a high refractive index. An
infrared beam from the instrument is passed into the accessory and up into the crystal. It is
then reflected internally in the crystal, and back towards the detector which is housed in the
instrument. When the beam is reflected within the crystal, it penetrates into the sample by a
few microns. Figure 2 illustrates this process.
Figure 2 Principle of UATR operation
The UATR can be used to analyze homogenous solid samples, solid surfaces, or coatings on
solid samples. Force may be applied to ensure good contact.
The Spectrum Two UATR uses a diamond crystal. The diamond crystal is hard, is not easily
scratched, is resistant to strong acids and bases, and can withstand high pressures. The
diamond UATR has an effective scanning range that matches the full range of the
instrument, although sensitivity is somewhat reduced in the approximate range 1900–
2700 cm
−
1
.
