Instrumentation
The main parts of IR spectrometer are as follows:
- radiation source
- sample cells and sampling of substances
- Monochromators
- detectors
- recorder
- IR radiation sources
IR instruments require a source of radiant energy which emit IR radiation which must be steady, intense enough for detection and extend over the desired wavelength. Various sources of IR radiations are as follows.
a) Nernst glower
b) Incandescent lamp
c) Mercury arc
d) Tungsten lamp
e) Glober source
f) Nichrome wire
- sample cells and sampling of substances
IR spectroscopy has been used for the characterization of solid, liquid or gas samples.
i. Solid - Various techniques are used for preparing solid samples such as pressed pellet technique, solid run in solution, solid films, mull technique etc.
ii. Liquid – samples can be held using a liquid sample cell made of alkali halides. Aqueous solvents cannot be used as they will dissolve alkali halides. Only organic solvents like chloroform can be used.
iii. Gas – sampling of gas is similar to the sampling of liquids.
- Monochromators – Various types of monochromators are prism, gratings and filters. Prisms are made of Potassium bromide, Sodium chloride or Caesium iodide. Filters are made up of Lithium Fluoride and Diffraction gratings are made up of alkali halides.
- Detectors – Detectors are used to measure the intensity of unabsorbed infrared radiation. Detectors like thermocouples, Bolometers, thermisters, Golay cell, and pyro-electric detectors are used.
Recorders – Recorders are used to record the IR spectrum.
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