IR spectroscopy and its applications

FTIR Spectroscopy
(Fourier Transform Infrared)
Infrared spectroscopy is an important technique in organic chemistry. It is an easy way to identify the presence of certain functional groups in a molecule. Also, one can use the unique collection of absorption bands to confirm the identity of a pure compound or to detect the presence of specific impurities.
This page will step you through the principles of operation of the FTIR Spectrometer, and how it differs from classical continuous-wave (CW) instruments. To skip directly to spectral interpretation,
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Continuous Wave spectrometers
Before delving into FT spectrometry, let s review the principles of a classical spectrometer. If you have used an optical or UV spectrometer, the principles are identical:
• A source generates light across the spectrum of interest.
• A monochromater (in IR this can be either a salt prism or a grating with finely spaced etched lines) separates the source radiation into its different wavelengths.
• A slit selects the collection of wavelengths that shine through the sample at any given time.
• In double beam operation, a beam splitter separates the incident beam in two; half goes to the sample, and half to a reference.
• The sample absorbs light according to its chemical properties.
• A detector collects the radiation that passes through the sample, and in double-beam operation, compares its energy to that going through the reference.
• The detector puts out an electrical signal, which is normally sent directly to an analog recorder. A link between the monochromater and the recorder allows you to record energy as a function of frequency or wavelength, depending on how the recorder is calibrated.