Bruker IFS 125M, User Manual, Page: 220 / 228

220 IFS 125M User Manual Bruker Optik GmbH
Glossary F
Validation In general, validation evidently documents that, by the use of
specific laboratory investigation methods, a process or system
(spectrometer) meets the previously defined requirements
(acceptance criteria) in reproducible manner and for its
intented analytical use.
During spectroscopic validation the x-axis (frequency) and y-
axis (transmission, reflection) are verified by transmission or
reflectance standards which may be included in the internal
spectrometer validation unit. Validation can be performed at
individual time intervals by the application software.
Wavelength
The wavelength is the distance between two maxima on a
sinusoidal wave, i.e. the distance traversed by one period of an
electromagnetic wave. The wavelength depends on the refrac-
tive index of the medium which the electromagnetic wave trav-
els through.
Wavenumber
The wavenumber is the reciprocal of the wavelength . The
wavenumber is defined as with the unit of cm
-1
, that
means the number of waves per each centimeter.
Wavenumber cali-
bration The wavenumber calibration comprises the entirety of working
steps to define the relation between the measured wavelength
(or wavenumber) scale of the spectrometer and an absolute
frequency scale. As the measured wavenumber scale of an
FT-IR spectrometer is quite linear, in principle only one calibra-
tion point is required.
In practice, the peak wavenumbers of many absorption lines of
a known reference gas are compared to their tabulated refer-
ence frequencies. A least squares algorithm should be
employed to calculate the calibration factor. The FT-IR spec-
trometer is calibrated by multiplying its reference laser wave-
number by the calibration factor.
If very high precision is required, the residual non-linearity of
the wavenumber scale has to be considered. Thus, the calibra-
tion has to be carried out for several smaller wavenumber
ranges separately. Each resulting calibration factor is valid only
for the corresponding smaller range.
Note that the alignment of the reference laser, the size of the
field stop (aperture), the pressure of the ambient air and other
factors influence the wavenumber calibration.
λ
ν
˜
λ
ν
˜
1
λ
0
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