2.
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 (transmitted). An FTIR spectrometer
simultaneously collects spectral data in a
wide spectral range.
3. FT-IR provide following information
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
4.
5. The spectrometer described here is a modified Bomem
MB-100 FTIR.
The heart of the FTIR is a Michelson interferometer.
The mirror moves at a fixed rate. Its position is
determined accurately by counting the interference
fringes of a collocated Helium-Neon laser.
The Michelson interferometer splits a beam of radiation
into two paths having different lengths, and then
recombines them.
A detector measures the intensity variations of the exit
beam as a function of path difference.
A monochromatic source would show a simple sine
wave of intensity at the detector due to constructive
and destructive interference as the path length
changes.
9. Components of FT-IR:
1) Radiation source
2) Monochromator
3) Sample cell and sampling of substance
4) Detector
10. The normal instrumental process is as follows:
1.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
(and, ultimately, to the detector).
2.The Interferometer: The beam enters the interferometer
where the “spectral encoding” takes place. The resulting
interferogram signal then exits the interferometer.
3.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.
4.The Detector: The beam finally passes to the detector for
final measurement. The detectors used are specially designed
to measure the special interferogram signal.
11. 1.Liquid Samples:
Neat sample
Diluted solution
Liquid cell
2.Solid Samples:
Neat sample
Cast films
Pressed films
KBr pellets
Mull
3.Gas Samples:
Short path cell
Long path cell
12. Pressed pellet techniques:Potassium bromide (KBr) is probably the most widely used
matrix material
-before use dried for 2 hours at 105º.
-Sample + 100 Times KBr (1;100)
-mixture is transferred to a die that has a barrel
diameter of 13 mm.
- Press at least 25000 psi.
- clear glassy disk about 1 mm thick obtained
- ready for transmission
Evacuable KBr Die
Potassium bromide 13 mm die.
13.
14. • Blank KBr was prepared
1
• Sample Kbr was prepared
2
• Balnk KBr was placed in sample holder and
the background was scanned
3
• Sample pellets were placed in sample holder
and background was scanned
4
5
6
• smoothning
• Label the peaks
• printing
15. Identification of inorganic compounds and organic
compounds
Identification of components of an unknown mixture
Analysis of solids, liquids, and gasses
In remote sensing
In measurement and analysis of Atmospheric Spectra
- Solar irradiance at any point on earth
- Longwave/terrestrial radiation spectra
Can also be used on satellites to probe the space
16. •Speed: Because all of the frequencies are measured
simultaneously, most measurements by FT-IR are made in a
matter of seconds rather than several minutes.
•Sensitivity: Sensitivity is dramatically improved with FT-IR
for many reasons. The detectors employed are much more
sensitive, the optical throughput is much higher which results
in much lower noise levels, and the fast scans enable the co
addition of several scans in order to reduce the random
measurement noise to any desired level (referred to as signal
averaging).
•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.
17. • Internally Calibrated: These instruments employ a HeNe
laser as an internal wavelength calibration standard. These
instruments are self-calibrating and never need to be
calibrated by the user.
