INSTRUMENTAL METHODS OF ANALYSIS, B.PHARM 7TH SEM. AND FOR BSC,MSC CHEMISTRY. Principle & app and instrumentaton of IR. This is Geeta prasad kashyap (Asst. Professor), SVITS, Bilaspur (C.G) 495001

1. Presented by : Mr. G.P Kashyap ( Asst. Prof )
M.Pharm (Q.A)
Siddhi Vinayaka Inst. of Technology & Sciences
(Bilaspur, C.G)

2. Principle of Infrared (IR) Spectroscopy
➢Infrared Spectroscopy is the analysis of infrared light interacting
with a molecule.
➢The portion of the infrared region most useful for analysis of
organic compounds have a wavelength range from 2,500 to 16,000
nm, with a corresponding frequency range from 1.9*1013 to
1.2*1014 Hz.
➢Photon energies associated with this part of the infrared (from 1
to 15 kcal/mole) are not large enough to excite electrons, but may
induce vibrational excitation of covalently bonded atoms and
groups.

3. Contn….
• It is known that in addition to the facile rotation of groups about
single bonds, molecules experience a wide variety of vibrational
motions, characteristic of their component atoms.
• Consequently, virtually all organic compounds will absorb infrared
radiation that corresponds in energy to these vibrations.
• Infrared spectrometers, similar in principle to other spectrometer,
permit chemists to obtain absorption spectra of compounds that
are a unique reflection of their molecular structure.

4. Cont….
• The fundamental measurement obtained in infrared
spectroscopy is an infrared spectrum, which is a plot of
measured infrared intensity versus wavelength (or
frequency) of light.
• IR Spectroscopy measures the vibrations of atoms, and
based on this it is possible to determine the functional
groups.
• Generally, stronger bonds and light atoms will vibrate at a
high stretching frequency (wave number).

5. Instrumentation of Infrared (IR) Spectroscopy
The main parts of IR spectrometer are as follows:
• Radiation source
• Sample cells and sampling of substances
• Monochromators
• Detectors
• Recorder
•

7. 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.
• Nernst glower
• Mercury arc
• Tungsten lamp
• Glober source
• carbon dioxide laser

8. The Nernst glower
• The Nernst glower is constructed of rare earth oxides in
the form of a hollow cylinder.
• Platinum leads at the ends of the cylinder permit the
passage of electricity.
• Nernst glowers are fragile.
• They have a large negative temperature coefficient of
electrical resistance and must be preheated to be
conductive.

10. THE GLOBAR SOURCE
• A globar is a rod of silicon carbide (5 mm
diameter, 50 mm long) which is electrically
heated to about 1,500 K.
• Water cooling of the electrical contacts is needed
to prevent arcing.
• The spectral output is comparable with the
Nernst glower, execept at short wavelengths (less
than 5 mm) where it's output becomes larger.

12. The carbon dioxide laser
A tuneable carbon dioxide laser is used as an
infrared source for monitoring certain
atmospheric pollutants and for determining
absorbing species in aqueous solutions.