FT-IR spectrometer

1. FTIR
F O U R I E R T R A N S F O R M
I N F R A R E D S P E C T R O M E T E R

2. OBJECTIVE
 Infrared spectroscopy
- introduction
- molecular vibrations
 Dispersive IR spectroscopy
FTIR
- introduction
- instrumentation
- Applications

3. INFRARED SPECTROSCOPY
• IR deals with the interaction of infrared radiation with
matter. The IR spectrum of a compound can provide
important information about its chemical nature and
molecular structure.
• Most commonly, the spectrum is obtained by
measuring the absorption of IR radiation, although
infrared emission and reflection are also used.
• Widely applied in the analysis of organic materials,
also useful for polyatomic inorganic molecules and for
organometallic compounds.

4. INFRARED REGIONS
• NEAR INFRARED: 0.8 -2.5 m, 12500 - 4000 cm-1
• MID INFRARED: 2.5 - 50 m, 4000 - 200 cm-1
• FAR INFRARED: 50 - 1000 m, 200 - 10 cm-1
Divisions arise because of different optical materials and
instrumentation.

5. MOLECULAR VIBRATIONS
• A molecule has as many degrees of freedom as the
total degree of freedom of its individual atoms. Each
atom has three degrees of freedom (corresponding to
the Cartesian coordinates), thus in an N-atom molecule
there will be 3N degree of freedom.
• In molecules, movements of the atoms are constrained
by interactions through chemical bonds.
• Translation - the movement of the entire molecule
while the positions of the atoms relative to each other
remain fixed: 3 degrees of translational freedom.

6. Degree of
freedom
Linear Non-linear
Translational 3 3
Rotational 2 3
Vibrational 3N-5 3N-6
Total 3N 3N
Rotational transitions
– interatomic distances
remain constant but the
entire molecule rotates
with respect to three
mutually perpendicular
axes: 3 rotational
freedom (nonlinear), 2
rotational freedom
(linear).
Vibrations – relative
positions of the atoms
change while the
average position and
orientation of the
molecule remain fixed.
Fundamental vibrations

7. VIBRATION
TYPES
Bond
stretching
1- Symmetric
2-
Asymmetric
Symmetric
Asymmetric

8. VIBRATION
TYPES
Bond bending
1-In-plane rocking
2-In-plane scissoring
3-Out-of-plane wagging
4-Out-of-plane twisting
In-plane rocking
In-plane scissoring
Out-of-plane wagging
Out-of-plane twisting

9. D I S P E R S I V E I R
S P E C T R O M E T E R S
 The original infrared
instruments were of the
dispersive type.
 Beam from an IR source is
split into two halves using a
mirror .
 One beam is passed
through a reference ; the
other is passed through a
sample .
 The two beams are
alternately passed to the
diffraction grating using a
beam chopper .
Recorder
Amplifier
Radiation
source
Beam divider
ReferenceSample
Beam Chopper
Mono
chromometer

10. D I S P E R S I V E I R
S P E C T R O M E T E R S
 Absorption of radiation is
detected by comparing the
two signals
 Light is dispersed (spread
into constituent
wavelengths) by a grating
much as it would by be by
a prism
 The grating is slowly
rotated, which changes the
angle if diffraction and
which wavelengths are
passed to the detector
 This results in a spectrum
which is a plot of intensity

11. WHAT IS FT-IR?

12. • FT-IR stands for Fourier Transform Infrared, the
preferred method of infrared spectroscopy.
• In infrared spectroscopy, IR radiation is passed
through a sample. Some of the infrared radiation is
absorbed by the sample and some of it is passed
through.
• The resulting spectrum represents the molecular
absorption and transmission, creating a molecular
fingerprint of the sample.
• Like a fingerprint no two unique molecular structures
produce the same infrared spectrum. This makes

13. what information can FT-IR provide?
• It can identify unknown materials
• It can determine the quality or consistency of a
sample
• It can determine the amount of components in a
mixture

14. PRINCIPLE

15. • An infrared spectrum represents a fingerprint
of a sample with absorption peaks which
correspond to the frequencies of vibrations
between the bonds of the atoms making up
the material.
• Because each different material is a unique
combination of atoms, no two compounds
produce the exact same infrared spectrum.
• Therefore, infrared spectroscopy can result in
a positive identification (qualitative analysis)
of every different kind of material

16. INSTRUMENTATION

17. THE SOURCE
 Infrared energy is emitted from a
glowing
black-body source. This beam passes
through an aperture which controls the
amount of energy presented to the
sample.

18. THE INTERFEROMETER
The interferometer requires
 Two mirrors,
 An infrared light source,
 An infrared detector,
 A beam splitter

19.  Source emits radiations which
strikes the beam splitter.
 the beam splitter reflects
about half of an incident light
beam while simultaneously
transmitting the remaining
half.
 One half of this split light
beam travels to the
interferometer's moving
mirror while the other half
travels to the interferometer's
stationary mirror.
 The two mirrors reflect both
beams back to the beam
splitter where each of the two
beams is again half reflected
and half transmitted.

20.  When the two beams return
to the beam splitter, an
interference pattern, or
interferogram, is generated.
 This interference pattern
varies with the displacement
of the moving mirror, that is,
with the difference in
pathlength in the two arms of
the interferometer.
 As the measured
interferogram can not be
interrupted directly, a means
of decoding the individual
frequency is required
 Which is accomplished by
applying Fourier transform
equation, gives a desired

21. THE SAMPLE
• The beam enters the sample compartment
where it is transmitted through or reflected off
of the surface of the sample, depending on
the type of analysis being accomplished. This
is where specific frequencies of energy, which
are uniquely characteristic of the sample, are
absorbed.

22. THE DETECTOR
• The beam finally passes to the detector for
final measurement. The detectors used are
specially designed to measure the special
interferogram signal.

23. THE COMPUTER
• The measured signal is digitized and sent to
the computer where the Fourier
transformation takes place. The final infrared
spectrum is then presented to the user for
interpretation and any further manipulation.

25. ADVANTAGES OF FT-IR
• It is a non-destructive technique
• It provides a precise measurement method which
requires no external calibration
• It can increase speed, collecting a scan every second
• It can increase sensitivity – one second scans can be
co-added together to ratio out random noise
• It has greater optical throughput
• It is mechanically simple with only one moving part

26. LIMITATIONS
• Minimal elemental information is given for most
samples.
• Background solvent or solid matrix must be relatively
transparent in the spectral region of interest.
• Molecule must be active in the IR region; i.e. when
exposed to IR radiation, a minimum of one vibrational
motion must alter the net dipole moment of the
molecule in order for absorption to be observed.

27. APPLICATION

28. POLYMERS & PLASTICS
• Material identification and verification
• Copolymer and blend assessment
• Additive identification and quantification
• Contaminant identification—bulk and surface
• Molecular degradation assessment

29. ENVIRONMENT
• Monitoring air quality,
• Testing water quality,
• Analyzing soil

30. FOOD
• Determination of the trans fat content of
manufactured food products.
• Near-Infrared spectroscopy is a solution that helps
companies optimize their production process and
guarantee products are meeting specifications.

31. QUALITY CONTROL
• Infrared spectroscopy is an ideal analytical
tool for both routine quality control (QC)
analysis to verify if materials meet
specification, and analytical investigations to
identify the causes of failures when they
occur.

32. OTHER APPLICATIONS
• Microscopy and imaging
• Nano scale and spectroscopy below the
diffraction limit
• FTIR as detector in chromatography
• TG-IR (thermogravimetric analysis-infrared
spectrometry)

33. Thank you
Presented by;-
Himanshu Kr. Bhatt
Rahul Sharma
Pankaj Tawar