Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. Infrared Spectroscopy is the analysis of infrared light interacting with a molecule.

1. Infrared Spectroscopy and
its applications
Presented by: Vikram Choudhary
M.Pharm 1st sem
Department of Pharmaceutical Chemistry,
School of Pharmacy,
DAVV, Indore

2. • Infrared spectroscopy (IR spectroscopy) is
the spectroscopy that deals with the infrared
region of the electromagnetic spectrum, that is
light with a longerwavelength and
lower frequency than visible light.
• Infrared Spectroscopy is the analysis of infrared
light interacting with a molecule.

3. They are divided into 3 regions
 Near IR Region
 Middle IR Region
 Far IR Region

4. Most of the analytical applications are confined to the
middle IR region because absorption of organic
molecules are high in this region.

5. • When infrared 'light' or radiation hits a
molecule, the bonds in the molecule absorb the
energy of the infrared and respond by vibrating.
IR
radiatio
n
vanllin
Molecular
vibrations

6.  Molecules are made up of atoms linked by chemical bonds.
The movement of atoms and the chemical bonds look like
springandballs(vibration).
 When internal vibrational energy of molecule matcheswith
energy of externallyapplied IR, quantized.
 MoleculesabsorbIR.
 A moleculecanonly absorbIR radiation whenitsabsorption
cause a change inits electricdipolemoment.
 Molecule excitedfromlowerto the higher vibrationallevel.
i.e. Increasestheamplitudeof vibration.
Cont’d

7. Molecular Vibrations
There are 2 types of vibrations:
1.Stretching vibrations
2.Bending vibrations
1.Stretching vibrations:
 Vibration or osciillation along the line of bond.
 Change in bondlength.
 Occurs at higher energy: 400 0-1250 cm-1

8. There are 2 Types of Stretching vibrations
a) Symmetrical stretching
a) Asymmetrical stretching

9. a) Symmetrical stretching:
2 bonds increase ordecrease in length
simultaneously.
H
H
C

10. b) Asymmetrical stretching
• One bond length is increased and otheris
decreased.
H
H
C

11. 2. Bending vibrations
• Vibration or oscillation not along the line
of bond.
• These are also called as deformations.
• In this, bond angle isaltered.
• Oc ursat low energy: 1400-666cm-1
• 2 types:
a)In plane bending: scissoring,rocking
b)Out plane bending: wagging, twisting

12. a) In plane bending
H
C
H

13. i. Rocking:
H
C
H
ii: Scissoring

14. b) Out plane bending
i. Wagging:
• 2 atoms move to one side of the plane. They
move up and down theplane.
H
C
H

15. ii)Twisting:
• One atom moves above the plane and
anotheratom moves below the plane
H
C
H

16. • We can also calculate an approximate value of
the stretching vibrational frequency of a bond
by treating the two atoms and their connecting
bond, to first approximation, as two balls
connected by a spring, acting as a simple
harmonic oscillator for which the Hooke’s Law
may be applied.
• According to Hooke’s Law , The Stretching
frequency is related to the masses of the atom
and the force constant(a measure of resistance
of a bond to stretching) of a bond by the
following equation
Hooke’s Law

18. • There are basically two types of spectrometers
1.single beam spectrometer
2.double beam spectrometer
In a single beam spectrometer the radiations
emitted from the source are passed through a
cell containing the sample and through the
prism which disperses thelight.
• Single beam spectrometers are
simple,sensitive and versatile.
INSTRUMENTATION OF IR SPECTROSCOPY

19. INSTRUMENTATION OF IR SPECTROSCOPY

20. • The double beam spectrometers are so
constructed that the light from the source is
split into two beams of equal intensity, one
passing through the sample and the other
through the reference for compensation.
• The two beams are recombined on to a
common axis and are alternatively focused on
to the entrance slit of the monochromator.
• Dbs are very convenient and hence used in
labs ,reserchwork and in routine works
INSTRUMENTATION OF IR SPECTROSCOPY

21. The main parts of IR spectrometer
are as follows:
 radiation source
 sample cells and sampling
of substances.
 monochromators
 detectors
 recorder
INSTRUMENTATION OF IR SPECTROSCOPY

22. IR instruments require a source of radiant
energy whichemit IR radiation whichmust
be:
INSTRUMENTATION OF IR SPECTROSCOPY

23. Sources of IRradiations are as follows:
GLOBAR:
INSTRUMENTATION OF IR SPECTROSCOPY

24. • NERNSTGLOWER:
INSTRUMENTATION OF IR SPECTROSCOPY

25. • For gassamples:
The spectrum of a gas can be obtained by
permitting the sample to expand into an
evacuated cell, also called a cuvette. Gas cell
has NaCl windows at theend.
• Forsolutionsample:
Infrared solution cells consists of two windows
of pressed salt sealed. Samples that are liquid at
room temperature are usually analyzed in pure
formor in solution.
INSTRUMENTATION OF IR SPECTROSCOPY

26. • ForSolid Sample:
Solids reduced to small particles (less than 2 micron) can
be examined as a thin paste or mull. The mull is
formed by grinding a 2-5 milligrams of the sample in
the presence of one or two drops of a hydrocarbon oil
(nujol oil). The resulting mull is then examined as a
film between flat salt plates.
Another technique is to ground a
milligram or less of the sample
with about 100 milligram
potassium bromide. The mixture
is then pressed in an evaluable
die to produce a transparent
disk.
INSTRUMENTATION OF IR SPECTROSCOPY

27. FORE OPTICS
•Consists of Source,Mirrors, M1,M2 and a Rotating mirrors
•M1,M2 divides thebeam.
• M alternately allows thesample beam and reference
beam topass through.
MONOCHROMATOR
• Splits the polychromatic radiation to component
wavelengths.
• Make use of prismsorgrating orboth.
• Resolutiondependsonslitwidthandquality of mirrors.
• Rocksaltprismis generally usedinthe range of 650-4000cm-1
INSTRUMENTATION OF IR SPECTROSCOPY

28. INSTRUMENTATION OF IR SPECTROSCOPY

29. Detector
Therm
al
Non-
thermal
INSTRUMENTATION OF IR SPECTROSCOPY

30. INSTRUMENTATION OF IR SPECTROSCOPY

31. There are four types ofthermal detector.
Bolometers
Thermocouple and thermopile
Pyro electricdetector
Golay Cell
INSTRUMENTATION OF IR SPECTROSCOPY

32. INSTRUMENTATION OF IR SPECTROSCOPY

33. THE RECORDER
•The amplified signal is recorded by an Pen Recorder.
•This instrument optical y balances out differential
between 2 beams. This kind of Instrument is cal ed
Optical nul recording Spectrometer.
•More sophisticated Instruments are cal ed Ratio-
recording Instruments. In these instruments the
intensities of both sample and reference beamsare
measured andratioed.
INSTRUMENTATION OF IR SPECTROSCOPY

34. INSTRUMENTATION OF IR SPECTROSCOPY

35. FT-IR
• FT-IR stands for Fourier Transform Infrared
Spectrometer, the preferred method of infrared
spectroscopy.
• Dispersive infrared spectrometers sufferfrom several
disadvantages in sensitivity, speed and wavelength
ac uracy.
• An entirely different principle is involved in Fourier
Transform infrared spectroscopy, which centres on a
Michelson interferometer, so that the method can also
be calledInterferometric infrared spectroscopy.
INSTRUMENTATION OF IR SPECTROSCOPY

36. INSTRUMENTATION OF FTIR

37. • 1. Identification of Substances
 To compare spectrums.
 No two samples will have identical IR spectrum.
 Criteria: Sample and reference must be tested in
identical conditions, like physical state, temperature,
solvent, etc.

38. The “Fingerprint” Region (1200 to 700 cm-1):
• Small differences in structure &
constitution of molecule result in
significant changes in the peaks in this
region.
• Hence this region helps to identify an
unknowncompound.

39. Structural/Functional Components

41. • IR Spectrum in Alcohol

42. Computer Search Systems
• Virtually all infrared instrumentmanufactures
now offer computer search systems to assist
chemist in identifying compounds fromstored
infrared spectraldata.
• The position and relative magnitudes of peaks
in the spectrum of the analyte are determined
and stored in memory to give a peak profile,
which can then be compared with profiles of
pure compoundsstored.

43. Studying Progress of Reactions
• Observing rate of disappearance of
characteristic absorption band in
reactants; or
• Rate of increasing absorption bands in
products of a particularproduct.
• Eg.: O—H= 3600-3650 cm-1C=O
= 1680-1760cm-1

44. Detection of Impurities
• Determined by comparing sample
spectrum with the spectrum of pure
reference compound.
• Eg.: ketone impurity inalcohols.

45. Measurement of Paints &
Varnishes
• Measured by ‘reflectance
analysis’.
• Advt: Measure IR
absorbance of paints on
appliances or automobiles
without destroying the
surface..

46. Examination of Old Paintings &
Artifacts
• Help to determine fake
“masterpieces”.
• Varnish& paints from
old items (statues,
canvas, etc.) are
analysed by IR
spectroscopy.
• Presence of new paint
traces implies the
“masterpiece” is fake.

47. In Industry
1. Determine impurities in raw materials (to
ensure quality products).
2. For Quality Control checks; to determine the %
of requiredproduct.
3. Identification of materials made in industrial
research labs, or materials of competitors.
E.g.: Impurity in bees wax (with petroleum
wax)

48. Medical applications
Hair:
• Narcotics in hair
• Effects of bleaching
• Effects of UV-radiation
Skin:
• Moisture content
• Lipid content
• Effects of cosmetics

49. ADVANTAGES
• Detection (healthcondition)
• Prevention (early diagnosis)
• Monitoring
• Diagnosis (underinvestigation)
• FT-IR Spectroscopy can be applied for the
determination of a biochemical metabolite
in biologicalfluids.
• FT–IR spectroscopy has been used for the
determination of glucose, total protein,
urea, triglyceride, cholesterol, and very low
density lipoproteins in plasma and serum.

50. References
 Stuart.B.2004.Infrared Spectroscopy: Fundamentals
and Applications, John Wiley and Sons Inc, New York,
Pp: 223-240.
Upadhyay. A, Upadhyay. K, and Nath. N. 2012.
Biophysical Chemistry (Principles and Techniques).
Himalaya Publishing House. Pvt. Ltd, Mumbai. Pp.175-
186.
 Sharma Y. R, “Elementary Organic Spectroscopy” Fifth
Edition 2017, Published by: S Schand and Company
Limited
 Holme.D.J & Peck.H. 1998. Analytical Biochemistry,
Third Edition, Pearson Education Limited.Pp:37-39.
 http://www.chem.ucla.edu/~webspectra/irtable.html
•