Agilent Technologies 5500a, Руководство по эксплуатации

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Analyzing Samples
Agilent 5500 Series FTIR Operation Manual 33
Agilent 5500a FTIR with an ATR
The Agilent 5500a FTIR instrument can be provided with a dedicated
sampling interface called the Attenuated Total Reflectance (ATR)
accessory. The ATR 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 (IR) 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 5500a
FTIR system. This small and consistent pathlength provides the
advantage of no sample preparation required to get good
measurement results on a variety of samples. The key to obtaining
good results with an ATR accessory is making good contact between
the sample and ATR crystal of the sampling device. The ATR
technique can be used for analysis of liquids, pastes, powders and
even some solid samples.
All Agilent ATR accessories use a type IIa diamond crystal as the
interface between the sample and the IR energy. The diamond
provides the advantage of extreme hardness as well as chemical
resistivity. Diamond can accept samples with a pH range from 1 to
14, which means hard or abrasive samples and even strong acids can
be safely analyzed. Agilent offers three choices of ATR sampling
accessories: a single reflection, triple reflection and nine reflection
DuraDisk system. All Agilent ATR disks use a patented diamond and
zinc selenide (ZnSe) composite design. The diamond is the world’s
most durable substance and the ZnSe substrate is used for maximum
IR signal.
The single reflection ATR is most suitable for higher absorbing
samples such as rubber, polymers, paints and fibers. Powder and
solid samples are best measured on the single reflection ATR as well
due to the sample press device that can apply high pressure to
powder and solid samples to ensure good contact with the diamond
sampling surface. The single reflection ATR is also a good choice
when the amount of available sample is limited. The single reflection
diamond has a 1 mm diameter sampling surface with 200
μ m active
area and provides approximately 2 micron depth of penetration for
IR energy at 1700 cm
-1
. The single reflection ATR protrudes slightly
above the metal mounting plate.