Easy way of learning Fourier Transformed IR spectroscopy

1. Fourier Transform Infrared (FT-IR) Spectrophotometry

2. Introducti
on• Absorption of IR radiation by sample, result in vibration transition.
• Infrared radiation lies between the Visible and microwave portions of the
electromagnetic spectrum.
• Infrared waves have wavelengths longer than visible and shorter than
microwave and have frequencies which are lower than visible and higher than
microwaves.
• IR spectra are mainly used in structure elucidation to determine the groups.

3. • 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 (0.78µm – 2.5µm)[13,000-
4000 cm^-1]
• Far-Infrared refers to the part of the infrared spectrum that
is closer to the microwave region (50µm-1000µm)(200-10
cm^-1)
• Mid-Infrared (2.5µm-50µm) [4000-200 cm^-1]

4. • If the radiation beams are in phase the beams will interfere constructively
and resultant amplitude will be twice as high.
Principl
e
c
c
Fixed Mirror
Movable Mirror

5. • If the radiation beams are out of phase, the beams will interfere
destructively and cancelling out each other.
c
c
Fixed Mirror
Movable Mirror

6. FT-IR Spectrometer
Components:-
• Source
• An optical System which uses interferometer
• Beam Splitter
• Stationary mirror
• Moving mirror
• Sample
• Detector

7. • Sources: Nernst Glower, Global Source, Tungsten Lamp, Mercury arc.
• Beam Splitter: It is made up of material which is made up of refractive index
1. For Far Infrared: Mylar film sandwiched between halide plate of low
refractive index solid used.
2. For middle IR : Thin film of germanium or silicon deposited on CsI or CsBr or
KCl or NaCl.
3. For Near IR: Thin film of ferric oxide deposited on calcium chloride
• Detector: Pyroelectric Detector is used

8. • It consist of two perpendicular mirrors, one of which is Stationary mirror and the
other is a movable mirror.
• The Position of movable mirror is controlled by HeNe Laser. (632.8 nm)
• Between these two mirrors , set a beam splitter at 45 degree from initial positon of
the movable mirror.
• A parallel beam of radiation from IR source is passed on the mirrors through the
beam splitter

9. FT-IR spectrometer Diagram

10. • The Beam Splitter Divides the beam and transmits half of the incoming radiation to the
fixed mirror and the other half to the movable mirror .
• Upon reflection from the fixed and the movable mirror the light is recombined at the
beam splitter.
• The recombination of the radiation is then direct through the sample and focused on the
detector on the detector (Pyroelectric detector).
• When the path difference is ZERO, all the spectral components are in phase and the
output is at a MAXIMUM.

11. Infrared Spectrum
Block Diagram

12. Advantages
• Better Sensitivity and brightness
1. Allows simultaneous measurement over the entire wavenumber range.
2. Requires no slit device.
• We can determine even small quantity of analyte.

13. • Resolution
The resolution is better and constant across the entire region under study.
• FT-IR coupled with HPLC,GC etc. in FTIR-GC, By this we can better vapour
phase spectra
• High scanning by FT-IR its possible to measure the whole spectrum in a few
seconds
• Photometric Accuracy advantage. These instruments employ a He-Ne laser as
an internal wavelength calibration standard. These instruments are self-
calibrating.
• The detectors employed are much more sensitive.

14. Disadvantag
es
FTIR instrument have only single beam while , dispersive instrument generally have a
double beam.

15. Application
• For opaque or cloudy samples
• Analysis of raw materials or finished products.
• Kinetics reactions on the microsecond time-scale.
• Analysis of chromatographic and thermogravimetric sample fractions.
• Micro-Samples. Tiny samples, Such as in forensic analysis
• Identification of compounds.

16. • Applications Of FT-IR spectroscopy in structural studies of cells and bacteria.
• FTIR can be used to identify chemicals from paints, polymers, coatings, drugs, and
contaminants.
• FTIR is perhaps the most powerful tool for identifying types of chemical bonds.
• Analysis trace impurities in mixtures.
• PHYSICAL PROPERTIES: Thickness, Crystallinity, Polymerisation, Phase change,
Hydrogen Bonding.