Analyzing Samples
38 Agilent Cary 630 FTIR Spectrometer User’s Guide
5 Bounce Zinc Selenide ATR Sampling Accessory
The 5 bounce zinc selenide attenuated total reflectance (5 bounce
ZnSe ATR) sampling accessory takes advantage of the physical
properties of light when encountering two materials with differences
in index of refraction. When coming in contact with a sample having a
different index of refraction, the infrared light creates an evanescent
wave, which provides a very small and specific depth of penetration
into the sample before reflecting back into the detector of the
spectrometer. The light is reflected into the multiple times to lengthen
the effective pathlength, giving lower detection levels than a single
bounce ATR.
Although easy to use, single bounce ATR does have the limitation of
low sensitivity compared to other FTIR techniques. Many methods
now require multi-bounce ATRs because of the greater sensitivity they
provide. The 5 bounce ZnSe ATR improves levels of detection while
still providing the ease-of-use of a single bounce ATR. In addition, the
accessory complies with the ASTM D-7371 Biodiesel method, making it
ideal for this application.
When in the sample analysis mode, the ATR sample pathlength is fixed
based on the number of reflections in the ATR. The alignment of the
accessory is also pre-set at the factory, and so there is no optical or
mechanical adjustment required.
Cleaning
Clean the 5 bounce ZnSe sampling window area using an extra-low
lint, non-abrasive wipe or cotton swab and a suitable solvent, such as
acetone, methanol, ethanol or isopropyl alcohol.
Figure 8. Cleaning the 5 bounce ZnSe ATR sampling window
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