2. IR instruments can be classified as:
1.Dispersive instruments
• Single beam IR spectrophotometer
• Double beam IR spectrophotometer
2.Non-Dispersive instruments
• Fourier transform infrared (FTIR) spectrometer
3.
4. FourierTransform Infrared (FT-IR) Spectroscopy
is a modern tool to study the characteristics of
molecules, either in solid, liquid or gas phase.
An FTIR spectrometer simultaneously collects
spectral data in a wide spectral range.
The term Fourier transform infrared
spectroscopy originates from the fact that a
Fourier transform (a mathematical process) is
required to convert the raw data into the actual
spectrum.
5. FTIR spectroscopy is preferred over dispersive methods
of infrared spectral analysis for several reasons:
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 has greater optical throughput
It is mechanically simple with only one moving part
FTIRV
7. FTIR seminar
Interferometer
He-Ne gas laser
Fixed mirror
Movable mirror
Sample chamber
Light
source
(ceramic)
Detector
(DLATGS)
Beam splitter
FT Optical System Diagram
8. The figure above shows what is referred to as the
Michelson interferometer
Radiations from the source falls on the interferometer
It comprises of beam splitter, moving mirror, fixed mirror
The beam splitter splits the light into two half beams of
equal intensities
One half of the beam is passed to the fixed mirror, Other
half is directed towards the mirror
9. Light enters the spectrometer and is split by the beam
splitter.
Speed of the moving mirror is controlled by using a
helium-neon laser beam
Because of the steady movement, detector receives
constants signals of maxima & minima
Beams after undergoes reflection from the respective
mirrors are recombined & send signal to the detector
10.
11. Combined signal is called as interferogram
After that the interferogram is either transmitted or
reflected to the sample cell
Samples absorbs only those IR frequencies which cause
vibration within the sample molecules
The signal is transmitted to the detector where it gets
measured
The coded signal were decoded by using computer
Technique is called as FourierTransformation
12. Filtration of radiation from the source is not
required
The data can be stored and reanalyzed
Enhanced frequency reproducibility
Enhanced frequency resolution
Less time consuming
13. Expensive
Required precision for mirror movement
Detection of the sample is influenced by water
vapour, path length & chemical interference
14. Opaque or cloudy samples
Trace analysis of raw materials or finished
products
Kinetics reactions on the microsecond time-
scale
Analysis of chromatographic and
thermogravimetric sample fractions
15. Instrumental methods of chemical analysis;
Gurdeep R. Chatwal;
Page no: 2.41-2.53
Pharmaceutical analysis
O.V.K.Reddy
Page no:1.681.72
Introduction to FTIR Spectrometry : www.thermonicolet.com
Principles of instrumental analysis;
2nd edition
Dougles skoog & Donald .M.West
Page no:210-219
Editor's Notes
Chapter 2
Principles of FTIR
2.4 Structure of an Interferometer
Fourier spectroscopy used in FT-IR is the general term for the use of a two-beam interferometer (primarily Michelson interferometers) in spectroscopy. A Michelson interferometer consists of a half-mirror (beam splitter) and two reflecting mirrors. One of the reflecting mirrors is fixed in place (fixed mirror) and the other has a mechanism for moving parallel to the optical axis (movable mirror).
Light from the light source is collimated and directed into the interferometer, striking the beam splitter at an angle, thereby separating the light into transmitted light and reflected light. These two beams of light are each reflected by the fixed mirror and movable mirror, and then returned to the beam splitter where they are recombined into a single beam.
