2011 Product Catalogue - Specac

Specac Product Catalogue 2011 | A-Z of IR
A-Z of IR
100% Line
Ratio of two background spectra under identical
conditions. Determines condition of
spectrometer, or accessory, and quality of
spectra. An ideal 100% Line would be a horizontal
line at 100%.
A
Absorbance
The amount of Infrared radiation absorbed by a
sample. It is proportional to concentration, and is
defined by Beer’s Law, so it can be used for
Quantitative Analysis. Often the Y-axis unit in
Infrared spectra, absorbance is related to
transmittance by A=log10 (1/T), where A is the
absorbance and T is the transmittance.
Attenuated Total Reflectance (ATR)
A reflectance sampling technique, used in such
accessories as the Golden Gate and the
Benchmark 6 Reflection ATR System. A beam of
Infrared radiation is passed through a prism of
material which is Infrared transparent, and has a
high refractive index, at least higher than the
sample being analyzed. Due to internal
reflectance, the light reflects off the surface of
the crystal at least once, setting up an
evanescent wave, which extends into the sample
by typically a few microns. The sample must be
held in intimate contact with the crystal.
B
Background Spectrum
A single beam spectrum produced without a
sample in the Infrared beam. It is used to record
the contributions that the instrument and the
environment make to the measurement.
The sample spectrum can be ratioed against the
background spectrum to remove these
contributions.
Baseline correction
The manipulation of a spectrum to correct a
sloped or curving baseline. The spectroscopist
draws a function parallel to the baseline which is
then subtracted from the spectrum.
Beamsplitter
An optical device which reflects half the radiation
striking it, and transmits half.
106
Benchmark
Specac’s universal compatibility baseplate
system, adapting Specac accessories to all
spectrometer models. Also Specac’s 6 Reflection
ATR System, capable of analyzing almost any
sample.
C
Calibration
In Quantitative Analysis, the correlation of peak
heights and areas in a spectrum with the
concentrations of standard analytes. After
calibration, unknown analyte concentrations can
be calculated.
Calibration curve
An Absorbance vs. Concentration plot used in
calibration. If the sample obeys Beer’s Law, the
plot will be linear and unknown concentrations
can be calculated.
Condenser
The optical element that condenses light on a
sample.
Critical Angle
Defined as being:
c = arcsin (n1/n2)
where c is the critical angle for an interface
between two specific media, n1 and n2 are the
refractive indices of the two media and n 2 has
the higher refractive index; the critical angle is the
smallest angle of incidence at which total
internal reflection occurs.
D
Depth of Penetration
When a sample is analyzed using ATR, the depth
of penetration is the depth at which the
evanescent wave has decreased to 1/e (or
36.788%) of its original value after penetrating
the sample. The depth of penetration is
dependent on many factors, including the angle
of incidence, the refractive index of the ATR
crystal, and the wavelength of the Infrared
radiation.
Cont’d
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