PerkinElmer Spotlight 400 Series, User Manual

Page: 53 / 120

Preparing Samples . 53
Common Window Materials
For work in the mid-infrared using the Spotlight 400 imaging system, both liquid and solid
samples are often mounted on salt windows. Very thin windows, 1 to 2 mm thick, give the
best spectra. The following materials are commonly used in windows:
• KBr: Potassium bromide is inexpensive, and it transmits infrared radiation to below
400 cm
−1
. The major disadvantage of this material is that it is hygroscopic, so that the
windows fog easily.
• BaF
2
: Barium fluoride is not hygroscopic. Its transmittance cut-off is 750 cm
−1
. It can
break or crack easily.
•
NaCl: Sodium chloride transmits infrared down to 600 cm
−1
. Otherwise, its properties
are similar to KBr.
•
ZnSe: Zinc selenide is not hygroscopic. Its transmittance cut-off is 650 cm
−1
. ZnSe is
more durable than the other windows but is yellow, so that the field of the Monitor
visible window appears yellow.
The measuring range of the Spotlight 400 system in Image mode is 7800 cm
−1
to 710 cm
−1
.
With the Long Wavelength option, this range becomes 7800 cm
−1
to 580 cm
−1
.
The Spotlight 400N FT-NIR imaging system has a range of 7800–2400 cm
−1
(with an MCT
detector) or 7800–3900 cm
-1
(with an InGaAs detector). For most near-infrared work in the
region 7800–4000 cm
−1
, samples can be mounted on standard quartz microscope slides.