The Principle of Infra-red and the principle and working of a FT-IR Spectra.

1. Fourier-Transform Infra-Red
RAKTIMAVA DAS SARKAR
M.Pharm 1st Semester
Department of Pharmaceutics
Roll- 19320322015

4. • Primary Source of IR Radiation is Heat or thermal Radiation
• 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.
• According to Principle of IR, Molecular Vibration takes place as a result of
Absorption of IR Radiation when
Applied Infrared Frequency = Natural Frequency of Vibration.
Every Bond or Functional Group required different frequency for absorption.
Hence, a characteristic Peak is observed for every functional group or part of
molecule.[4]

5. • In IR Spectroscopy, Infrared Radiation is produced and passed through a sample. Some
of the radiation is absorbed by sample and some is transmitted.[2]
• The resulting spectrum represents molecular transmission and absorption, thus
creating a molecular fingerprint. As no two fingerprints are similar. Thus, no two
unique samples produces same IR Spectrum.
Wavenumber Stretch Type
>= 3000 cm-1 single bond stretch
eg. C-H, O-H, and N-H
2000 - 2500 cm-1
triple bond stretch
eg. acetylenes,
carbenes and nitriles
1500 - 2000 cm-1
double bond stretch
eg. carbonyls (C=O) or
alkenes (C=C)

6. In IR changes in the Vibrational Frequency energy depends upon
1. Mass of atom present in the molecule
2. Strength of the Bonds
3. Arrangement of atoms within the molecule
There are two types of Vibrations:-
Vibrations
Stretching
Symmetric
Asymmetric
Bending
Scissoring
Twisting
Rocking
Wagging

7. When the IR Radiation is emitted it goes through an
interferometer that has an beam-splitter that
divides the beam into two optical beams.
One beam reflects off a flat mirror which is fixed and
another reflects off a movable mirror. After
reflection they are recombined at the beam-splitter.
The resulting signal is called an interferogram
which has unique property that the resulting beam
has all the frequencies of Infrared that comes from
the source.
As we need a frequency spectrum of individual frequency, the interferogram signal cannot be
interpreted easily.
A mean of Decoding is accomplished via mathematical technique called Fourier Transformation. This
Transformation is done entirely by Computer.[1][3]

9. Application of FT-IR
1. To identify unknown compounds.
2. To determine quality and consistency of a sample.
3. To determine the amount of components in a
mixture.

10. 1. Berthomieu, Catherine & Hienerwadel, Rainer. (2009). Fourier transform infrared (FTIR)
spectroscopy. Photosynthesis research. 101. 157-70. 10.1007/s11120-009-9439-x.
2. Rohman, Abdul & Ghazali, Mohd & Windarsih, Anjar & Irnawati, Irnawati & Riyanto,
Sugeng & Yusof, Farahwahida & Mustafa, Shuhaimi. (2020). Comprehensive Review on
Application of FTIR Spectroscopy Coupled with Chemometrics for Authentication
Analysis of Fats and Oils in the Food Products. Molecules. 25. 5485.
10.3390/molecules25225485.
3. Using Fourier Transform Infrared Spectroscopy to Study Effects of Magnetic Field
Treatment on Wheat (Triticum aestivum L.) Seedlings, Zhenlin Wei, Dejie Jiao, and
Junxiao Xu, Hindawi Publishing Corporation Journal of Spectroscopy Volume 2015, Article
ID 570190, 6 pages http://dx.doi.org/10.1155/2015/570190.
4. Jozanikohan, G., Abarghooei, M.N. The Fourier transform infrared spectroscopy (FTIR)
analysis for the clay mineralogy studies in a clastic reservoir. J Petrol Explor Prod Technol
12, 2093–2106 (2022). https://doi.org/10.1007/s13202-021-01449-y