The document discusses Fourier transform infrared spectroscopy (FTIR). It begins by explaining the basic principles of FTIR including how a Fourier transform is used to convert infrared absorption data into a spectrum. It then describes key components of an FTIR instrument and how it works. The document outlines advantages such as high resolution and speed of analysis. Applications including structure determination and identification of organic compounds are also mentioned.

1. Presented By:
Mr. Sachin R. Naksakhare
M.Pharm Sem-I
Guided By:
Dr. S. B Wankhede
Professor & HOD
Dept. of Quality Assurance Techniques
Dr. D .Y Patil Institute Of Pharmaceutical Science and
Research, Pimpri, Pune

2. o Introduction
o Theory
o Basic Principle
o Instrumentation
o Advantages of FTIR
o Advantages and Disadvantages
o Application
o Reference

3.  The Fourier transform spectroscopy (a mathematical
process) is required to convert the IR data into the actual
spectrum this technique is called Fourier transform
spectroscopy.
 FTIR is a technique which is used to obtain an infrared
spectrum of absorption or emission of a solid, liquid or
gas.

4.  Absorption peaks in an infrared absorption
spectrum arise from molecular vibrations.
 The absorption of IR radiation causes the
excitation of molecule from a lower to the higher
vibration level.
 This absorption corresponds specifically to the
bonds present in the molecule.
 Absorbed energy causes molecular motions which
create a net change in the dipole moment.

6.  The Varying distances between two path lengths result
in a sequence of constructive & destructive interferences
& hence variations in intensities an interferogram.
 Fourier transformation converts this interferogram from
the time domain to one spectral point on the more
familiar form of the frequency domain.
 Fourier transformation at successive points through out
this variation gives rise to complete IR spectra.

7.  FTIR relies on the fact that the most molecules absorb
light in the infra-red region
0.8µm(800nm)to1000µm(1mm) of the electromagnetic
spectrum.
 Uses an interferometer to replace the dispersive devise
and generate an interference beam that is then exposed
to the sample.
 The data undergo analog to digital conversion.
 FTIR can be used in conjugation with HPLC and GC
 FTIR have very high resolution.

11.  The IR source radiation travels through the beam
splitter to the fixed mirror back to the beam splitter
through the sample and to the detector.
 The IR source radiation travels to the beam splitter to
the movable mirror, back through the beam splitter to
the sample and to the detector.
 The difference in path lengths of the two beams is the
retardation .
 The He-NE laser is used as a monochromatic reference
source.

12. Sources
 Infrared instrument require a sources of radiant energy
which provides a means for isolating narrow frequency
bands.
 The radiation source must emit IR radiation which must be
a) intense enough for detection
b) the desired wavelengths
 Inert solids heated to electricaly 1500-2000 °K
1] Nernst Glower:– (Tem 1000-1800 °K)
The Nernst glower is composed of rear earth oxides (
Zirconium, ytterbium and thorium ) elements.

13. • It consist of hollow rod which is about 2mm in diameter and
30mm length.
• It provides maximum radiation at about 7100cm-1
2] Globar:- (Tem 1300-1700K°K)
• It is rod of Sintered Silicon carbide which is about 50mm in
length and 4mm in diameter.
• It emits maximum radiation at 5200cm-1
3]Incandescent Lamp(Near IR):- (Tem 1100°K )
• In the near infrared region is generally used.
4]Mercury arc (Far IR):–
This device consists of Quartz jacketed tube containing high Hg
vapor at a pressure greater than 1atm.

14. Michaelson Interferometer
 It is used to measure the influence of the earth’s rotation
on the speed of light.
 It takes the radiation from an infrared source and splits it
into two beams ( one beam is fixed the other is of
variable length) using a half silvered 450 mirror so that
the resulting beams are at right angles to each other.
 Consist of 2 plan mirrors at right angle to each other.

15.  The IR radiation is separated by a beam splitter in tow
perpendicular half beams equal intensity of light reflected
by moving mirror and another is reflected by fixed mirror
they recombine and are reflected together on to the
detector.
 And generates interference pattern.
 The resulting interferogram will carry the spectral
characteristics of the sample in the beam.
 He-Ne laser is used to track the position of the moving
mirror.

16. Source
Stationary mirror
Moving mirror
Sample
Detector
Beam Splitter
PMT
He Ne laser

18. Sample
 Sample holder must be transparent to IR- salts
 Liquids
– Salt Plates
– Neat, 1 drop
– Samples dissolved in volatile solvents- 0.1-10%
 Solids
– KBr pellets
– Mulling (dispersions)
 Quantitative analysis-sealed cell with
NaCl/NaBr/KBr windows

19. DETECTOR
1] THERMOCOUPLE:
 It is made by welding together two wires of metals 1& 2
(like bismuth & antimony) in such a manner that a
segment of metal 1 is connected to two terminal wires of
metal 2.
 One junction between metals 1 & 2 is heated by the IR
beam & the other jn . is kept at constant temperature;
small changes in ambient temperatures are thus
minimized.

20.  To avoid losses of energy by convection, the
thermocouples are enclosed in an evacuated vessel with
a window transparent to IR radiation.
 The metallic junctions are also covered with a black
deposit to decrease reflection of the incident beam.
 Response time is 60 m sec
Metal A
Metal B welded junction
(cold)
welded junction
(hot)

21. 2] PYROELECTRICAL DETECTOR
 It use ferroelectric materials operating below their curie-
temperatures.
 When IR radiation is incident on the detector there is a
change in polarization which can be employed to produce
an electrical signal.
 The detector will only produce a signal when the intensity of
the incident radiation changes.
 They are of a special value in FTIR.
 Fast response
 they use Deuterium triglycine sulphate as the detecting
medium in an evacuated chamber.

22. Incoming light
Sensing circuit
Pyroelectric disc
Front surface
elcetrodes
Rear surface
elcetrodes

23.  Mercury cadmium tellurium (MCT)
 High sensitivity
 Faster response
 Necessary to cool by liquid N2.
3] mct detector

24. 1. Multiplex advantage (Fellgett):-
All frequencies are measured simultaneously typical scan
times are only a few seconds.
2. Aperture advantage (Jacquinot):-
The energy through put is higher for any resolution
giving a higher signal : noise ratio.
3. Laser reference advantage (Connes):-
The laser wavelength is used as a reference for the

25. 1.High sensitivity
2.High wavenumber accuracy
3. Resolution
4. Stray light
5. Speed of data acquisition
FTIR Advantages

26. Disadvantages of FTIR
 Cannot detect atoms or monoatomic ions single atomic
entities contain no chemical bonds.
 Cannot detect molecules comprised of two identical atoms
symmetric-such as N2 or O2.
 Aqueous solutions are very difficult to analyze.

27. interpret IR spectrum
Example:- Ethanol
stretching wavenumbers
O-H 3391cm-1
C-H 2981cm-1
C-O 1055cm-1

29. APPLICATIONS
Identification of an organic compound.
Structure determination.
Determination of functional groups.
Quantitative analysis.
 Qualitative analysis.
 Distinction between two types of hydrogen bonding
 Study of a chemical reaction
 Study of complex molecules
 Detection of impurity in a compound

30.  Instrumental Methods of Chemical Analysis, Gurudeep
R. Chatwal & Sham K. Anand; Fifth edition; Himalaya
Publishing House.
 Elementary Organic Spectroscopy, Y. R. Sharma; Fourth
Edition; S. Chand & company ltd.
 Practical Pharmaceutical Chemistry, A H Beckette, J B
Stenlake; fourth edition; Part – II; CBS Publishers &
Distributors.

31.  Wikipedia. Fourier Transform Infrared Spectroscopy.
http://en.wikipedia.org/wiki/fourier_transform_infred_spe
ctroscopy. 2006