FTIR spectroscopy

Fourier transform infrared spectroscopy: advantage and disadvantage of conventional infrared spectroscopy, introduction to FTIR ,principle of FTIR, working, advantage, disadvantage and application of FTIR.

1. Fourier Transform Infrared
(FT-IR) Spectroscopy
•Submitted by: Preeti Choudhary
•Roll No.= 17/MAP/016
•M.Sc. (Applied Physics)

2. What is Infrared Region?
Infrared radiation lies between the visible and microwave
portions of the electromagnetic spectrum.
Infrared waves have wavelengths longer than visible and
shorter than microwaves, and have frequencies which are lower
than visible and higher than microwaves.
The Infrared region is divided into: near, mid and far-
Infrared
 Near-infrared refers to the part of the infrared spectrum that is
closest to visible light and far- infrared refers to the part that is
closer to the microwave region
Mid-infrared is the region between these two.
Range = 10
-4
to 10
-6
m

3.  The primary source of infrared radiation is thermal
radiation. (Heat)
It is the radiation produced by the motion of atoms and
molecules in an object. The higher the temperature, the more the
atoms and molecules move and the more infrared radiation they
produce.
Any object radiates in the infrared. Even an ice cube, emits
infrared.

4. 4
•Slow Scanning process (time consuming)Slow Scanning process (time consuming)
–"step-wise" nature of spectral acquisition (Measure one "step-wise" nature of spectral acquisition (Measure one
frequency at a time-scanning takes 5 -15min)frequency at a time-scanning takes 5 -15min)
•Limited energy throughput.Limited energy throughput.
–optical dispersion process throws energy away optical dispersion process throws energy away
–the exist and entrance slits allow throughput of only a small the exist and entrance slits allow throughput of only a small
fraction of the total IR energy (<< 50%)fraction of the total IR energy (<< 50%)
•Difficult to increase the S/N by multiple scanningDifficult to increase the S/N by multiple scanning
–wavelength reproducibility is not sufficient due to mechanical wavelength reproducibility is not sufficient due to mechanical
irrelevant response.irrelevant response.
Dispersion ElementDispersion Element
Entrance SlitEntrance Slit
Exit SlitExit Slit
detectordetector
SampleSample
SourceSource
Disadvantages of Dispersion Infrared Disadvantages of Dispersion Infrared
InstrumentationInstrumentation

5. What is FT-IR?

6. FT-IR stands for FourierTransform 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 (transmitted).
The resulting spectrum represents the molecular absorption and
transmission, creating a molecular fingerprint of the sample.
Like a fingerprint no two unique molecular structure produce the
same infrared spectrum. This makes infrared spectroscopy
useful for several types of analysis.
FT-IR

8. Principle of FTIR
•Fourier transform spectroscopy differs
from conventional (dispersive)
spectroscopy in that all of the resolution
elements or wavelength intervals for a
spectrum are measured simultaneously.

9. So, 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

10. Dispersive Spectrometer FTIR
InordertomeasureanIR
spectrum, the dispersion
Spectrometer takes several
minutes.
Also the detector receives
only a few % of the energy of
original light source.
In order to measure an IR
spectrum, FTIR takes only afew
seconds.
Moreover, the detector receives
up to 50%ofthe energyof
original light source. (much
larger than the dispersion
spectrometer.)

11. 
Fourier Transform Infrared (FT-IR) spectrometry was developed
in order to overcome the limitations encountered with dispersive
instruments mainly the slow scanning process.
Fourier Transform IRFourier Transform IR

A solution was developed which employed a very simple optical
device called an interferometer. The interferometer produces a
unique type of signal which has all of the infrared frequencies
“encoded” into it. The signal can be measured very quickly, usually on
the order of one second or so.

12. How Instruments work?
Modern IR Spectrophotometry
Modern infrared spectrometers are very different from the early
dispersive instruments that were introduced in the 1940s.

While there is still a need for dual-beam dispersive instruments in high-
precision work, most instruments today use a Fourier Transform infrared
(FT-IR) system.
A Fourier transform is a mathematical operation used to translate a
complex curve into its component curves.

In a Fourier transform infrared instrument, the complex curve is an
interferogram, or the sum of the constructive and destructive
interferences generated by overlapping light waves, and the component
curves are the infrared spectrum.

13. FT-IR
 Conventional spectroscopy can be termed
frequency-domain spectroscopy. In that radiant
power data are recorded as a function of frequency
(or the inversely related wavelength).
 In contrast, time domain spectroscopy, which can
be achieved by the Fourier transform, is concerned
with changes in radiant power with time.

14. Frequency domain spectra Time domain spectra

15. 15
FTIR systemsFTIR systems
1.Mechanical operation
•Encode (modulate) the spectral information using a
Michelson Interferometer.
2.Mathematical operation
•Computer processing of encoded information to
produces the spectrum (Decoding).

16. 16

Most interferometers employ a beamsplitter which takes the
incoming infrared beam and divides it into two optical beams.
One beam reflects on a flat mirror which is fixed in place. The
other beam reflects on a flat mirror which is on a mechanism
which allows this mirror to move a very short distance (typically a
few millimeters) away from the beamsplitter.
Michelson Interferometer Michelson Interferometer
(Mechanical operation)(Mechanical operation)

Because one beam travels is a fixed length and the other is
constantly changing as its mirror moves, the signal which exits the
interferometer is the result of these two beams “interfering” with
each other. The resulting signal is called an interferogram which has
the unique property that every data point which makes up the signal
has information about every infrared frequency which comes from the
source.

17. 17
Fourier transform Fourier transform
(Mathematical Operation)(Mathematical Operation)
Because the analyst requires a frequency spectrum (a plot of the
intensity at each individual frequency) in order to make an
identification, the measured Interferogram signal can not be
interpreted directly. A means of “decoding” the individual
frequencies is required. This can be accomplished via a well-
known mathematical technique called the Fourier
transformation. This transformation is performed by the
computer which then presents the user with the desired spectral
information for analysis.

18. FTIR seminar
Interferometer
He-Ne gas laser
Fixed mirror
Movable mirror
Sample chamber
Light
source
(ceramic)
Detector
Beam splitter
FT Optical System Diagram

19. To separate IR light, a grating is used.
Grating
Light source
Detector
Sample
Slit
To select the specified IR light,
A slit is used.
Dispersion
Spectrometer
In order to measure an IR spectrum,
the dispersion Spectrometer takes
several minutes.
Also the detector receives only
a few % of the energy of
original light source.
Fixed mirror
.
Moving mirror
IR Light source
Sample
Detector
An interferogram is first made by
the interferometer using IR light.
The interferogram is calculated and transformed
into a spectrum using a Fourier Transform (FT).
FTIR
In order to measure an IR spectrum,
FTIR takes only a few seconds.
Moreover, the detector receives
up to 50% of the energy of original
light source.
(much larger than the dispersion
spectrometer.)
Comparison Beetween Dispersion Spectrometer
and FTIR

20. Relationship between light source spectrum and the signal output from interferometer
(a)Monochromatic
light
(b) Dichroic light
(c)Continuous
spectrum light
All intensities are standardized.
Light source spectrum Signal output from interference wave
Time t
Time t
Time t
I(t)
I
b (u
)
Wavenumber u
Wavenumber u

Wavenumber u
S
I
SA
z
A
z
FTIR seminar
Interference is a superpositioning of waves

21. 1.Better sensitivity and brightness
- Allows simultaneous measurement over the entire wavenumber range
- Requires no slit device, making good use of the available beam
2.High wavenumber accuracy
- Technique allows high speed sampling with the aid of laser light interference fringes
- Provides wavenumber to an accuracy of 0.01 cm-1
3. Resolution
- Provides spectra of high resolution
4. Stray light
- Fourier Transform allows only interference signals to contribute to spectrum.
Background light effects greatly lowered.
-Allows selective handling of signals, limiting intreference
5. Wavenumber range flexibility
- Simple to alter the instrument wavenumber range
CO
2
and H
2
O sensitive
FT-IR Advantages and Disadvantages

22. 22
• Speed Because all of the frequencies are measured simultaneously.
• Sensitivity is dramatically improved with FT-IR ; detectors are much more
sensitive, the optical throughput is much higher, higher signal to noise ratio.
• Mechanical Simplicity The moving mirror in the interferometer is the only
continuously moving part in the instrument. Thus, there is very little
possibility of mechanical breakdown.
• Internally Calibrated These instruments employ a He-Ne laser as an
internal wavelength calibration standard .These instruments are self-
calibrating and never need to be calibrated by the user.
Summary of FT-IR Summary of FT-IR

23. FT-IR Applications
•Opaque or cloudy samples
•High resolution experiments (as high as 0.001 cm
-1
resolution)
•Trace analysis of raw materials or finished products
•Depth profiling and microscopic mapping of samples
•Kinetics reactions on the microsecond time-scale
•Analysis of chromatographic and thermogravimetric sample
fractions

24. REFERENCES :-
•Introduction to Fourier Transform Infrared Spectrometry By Thermo
Nicolet Corporation
•An article on FTIR SAMPLING TECHNIQUES by Hue Phan. TN.101
•Instrumental Methods Of Chemical Analysis by Gurdeep R. Chatwal &
Sham K. Anand
•P. R. Griffiths and J. A. de Haseth, Fourier-Transform Infrared
Spectroscopy, Wiley- Interscience, New York,
Chichester,Brisbane, Toronto, Singapore,1986
•FTIR Spectroscopy By Jorge. E. Perez and Richard T. Meyer
CIC
•Photonics, Inc. 3825 Osuna Rd. NE Ste. 6 & 7. Albuquerque, NM 87105.

25. Thank
You