Ftir; Figure 7-5. Ftir Analyzer - Thermo Scientific Omni FTIR Multi Gas CEMS Instruction Manual

System Component Description

FTIR

FTIR
The FTIR analyzer (Figure 7–5) measures the interaction of infrared (IR)
radiation with samples. More specifically, it measures the frequencies or
wavelengths at which the sample absorbs radiation and the intensities of the
absorptions to determine concentrations of specific gases.
Intensity and frequency (or wavelength) of sample absorption are depicted
in a two-dimensional plot called a spectrum. Intensity is generally reported
in terms of transmittance (the amount of light that passes through the
sample) or its inverse, absorbance (the amount of light absorbed by the
sample).
Frequency is usually reported in terms of wave numbers (cm-1). With
quantitative analysis, the intensity of absorption is related to the
concentration of the component. After the data collection method is
calibrated, which establishes how concentration changes affect absorbance
changes, the absorbance for an unknown sample can be used to calculate
concentration.
Figure 7–5. FTIR Analyzer
Infrared light from the source is directed to the Michelson interferometer, a
key component of FTIR spectrometry. In the interferometer, the light
beam strikes the beamsplitter. About half of the light is reflected from the
beamsplitter and is directed onto the fixed mirror. The remainder of the
light is transmitted through the beamsplitter and is directed onto the
moving mirror. The two beams are reflected from the mirrors to the
beamsplitter, where they recombine. When the beams recombine,
constructive or destructive interference occurs, depending on the
relationship between the position of the moving mirror relative to the fixed
mirror and the wavelength of the light.
Thermo Fisher Scientific Omni FTIR Multi Gas CEMS Instruction Manual 7-7