Infrared radiation that is either absorbed or emitted by solid, liquid or gaseous samples is obtained by FTIR. It gives a high-spectral-resolution data over a wide spectral range.
a) Principle: Molecules in general absorb light of a particular wavelength from an electromagnetic spectrum. FTIR employs this phenomenon of infrared light absorption by the sample which is characteristic to its functional groups and side-chain involved. Thus, making it a fingerprint analysis as no two compounds have the same molecular structure. It is called as “Fourier transform” as a mathematical process is used to convert the raw data into actual spectrum.
b) Working: Infrared radiation from the light source is initially modulated by the interferometer and then passed through the sample. The sample absorbs radiation specific to its functional groups and emits the remaining radiation that reaches the detector, where the signals are measured and the output in the form of interferograms are recorded.
Fig. 6: Instrumentational diagram of FTIR.
c) Applications of FTIR:
• FTIR is employed in the identification of organic and inorganic compounds
• In remote sensing
• Any nature of the sample i.e., solid, liquid or gas can be tested
• Is used by scientist to probe the space via satellites.
d) Specifications for sample analysis by FTIR:
? Model : Alpha-Bruker
? Software : Opus – 7.5 version
? Window material : Zinc-selenium (ZnSe) ATR plates
? Detector range : 1 x 1mm
? Spectral range : 4000 to 500 cm-1
? Resolution :16 scans
? Optic used : parabolic off axis
? Irradiance : 1 x 10-4
? RMS voltage : 1.8 x 10-2
? Modulation : 500 Hz
? Operating bandwidth (with amplifier) : 100 Hz to 40 kHz optimized for 5 kHz
? Interferogram size : 15150 points
? FT size : 16 K