1. THEORY, INSTRUMENTATION AND APPLICATIONS OF DISPERSIVE & FTIR
Presented By
Bhavana Vedantam,
Dept. Of Pharmaceutical Analysis

2. Contents It Contains… Introduction to IR Spectroscopy
Dispersive IR Spectroscopy
FT - IR Spectroscopy
Conclusion

3. INTRODUCTION
Spectroscopy is the branch of science dealing with the study of interaction of electromagnetic radiation with matter. IR spectroscopy is Absorption spectroscopy in which molecular vibrations observed due to absorption of IR radiation.
Infrared radiation was discovered in 1800 by William Herschel.

4. The range of EMR between the visible and microwaves region is called INFRARED region( cm-1 ).

5. IR REGION
From application and instrumentation point of view infrared region is subdivided into
Region
Wave length (m)
Wave number(cm-1 )
Near infrared
Mid infrared
2.5-50
Far infrared
50-300
400-40
Mid IR
( cm-1)
Functional group region
( cm-1)
Finger Print/Single bond region
( cm-1)
Stretching vibrations occurs in F.G. region
Bending vibrations occurs in F.P. region

6. General Purpose Of IR Radiation
Infrared light is used in industrial, scientific, and medical applications.
In Telescopes to detect  planets
Finding heat leaks from houses

7. Contd...
Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, and to detect overheating of electrical apparatus.
Night-vision devices
Remote temperature sensing, short-ranged wireless communication, spectroscopy, and weather forecasting.

8. Pharmaceutical Applications
Qualitative determination of substances
Structural elucidation by determining the functional groups.
Detection of impurities
Identification of geometrical isomers for both organic & inorganic samples
Detection of presence of water in sample
Quantitative determination of sample by using Beer’s-Lamberts law

9. PRINCIPLE
In any molecule , atoms or groups of atoms are connected by bonds which are similar to springs and not rigid in nature.
Bonded atoms having different strengths due to different masses.
Absorption of IR energy will cause vibrational changes in molecule and a peak will be observed, when

10. Conditions to obtain IR spectrum
Contd…
Conditions to obtain IR spectrum
Selection rule for IR spectroscopy: Dipole moment of bonds should change during vibration.
When Applied infrared frequency = Natural frequency of vibration
When covalent bonds are polar in nature
When sample obeys these conditions, then it gets vibrated by absorbing radiation and gives IR spectrum.

11. Hooke’s law
Hooke's law
 of elasticity is an approximation which states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit.
K = force constant
(in dynes/cm)
m = atomic masses of atom 1 & 2
Used to calculate approximate position of band

12. TYPES OF VIBRATIONS Stretching Mode In plane bending vibrations
Scissoring
Rocking
Out plane bending vibrations
Symmetric
Asymmetric
Wagging
Twisting

13. Instrumentation Radiation sources
They must produce intense & steady radiation.
Nernst Glower
heated rare earth oxide rod (zirconium, yttria, thoria) (~1500 K)
1-50 µm
(mid- to far-IR)
Globar
heated Silicon Carbide rod (~1500 K)
W filament lamp
1100 K µm
(Near-IR)
Hg arc lamp
Hg plasma µm
(far-IR)

14. Monochromators Filtration of desired frequency of radiation
Monochromators are 2 types
Prismatic Monochromator
Grating Monochromator
Prismatic Monochromators:
Composed of glass or quartz and coated by alkyl halides (NaCl)
These are 2 types
Mono pass Prismatic Monochromator: radiation will pass once through the prism
Double pass Prismatic Monochromator: radiation will pass twice through the prism

15. Grating Monochromators
Grating monochromators introduced in 1950’s
High dispersion and resolution than prismatic monochromators
These are 2 types
Reflection Grating Monochromator are common than Transmittance Gratings
Gratings are linear grooves or lines which are made up of Aluminium.

16. Detectors/Transducers
Thermocouple
Thermoelectric effect -dissimilar metal junction
cheap, slow, insensitive
Bolometer
Ni, Pt resistance thermometer (thermistor)
Highly sensitive <400 cm-1
Golay cell
Metal cylinder with Xe gas
Faster than others & having wide wavelength range
Pyro electric
Tri glycine sulfate piezoelectric material
fast and sensitive (mid IR)
Photoconductive (non-thermal)
PbS, CdS, Pb Se light sensitive cells
fast and sensitive (near IR)

17. TYPES OF IR INSTRUMENTS
Non- Dispersive
Filters used for wavelength selection & having sample specific Detector
Dispersive
Sequential scanning of each wave number takes place
FTIR systems
Widely applied and quite popular in the far-IR and mid-IR spectrometry.

18. Dispersive IR Instrument
Dispersive IR instruments are introduced in 1940’s. Double-beam instruments are mostly used than Single beam instrument. In dispersive IR sequential scanning of wave numbers of light takes place.

19. Instrumentation
In double beam spectrometer , beam separates into two and passes to sample & reference.
Prismatic monochromators have been replaced with Grating monochromator.
Dispersive IR failed due to monochromator containing narrow slits which limit the wave number of radiation.

20. (X) It containing all movable parts which causes mechanical slippage (X) Slow scan speed (X) Less resolution, accuracy and sensitivity (X) Only narrow frequency range can be studied (X) Involvement of stray light (X) Atmospheric absorptions by CO, water also takes place.
To overcome all these problems FTIR has been developed

21. Fourier Transform IR Instrument
FTIR collects all wavelengths simultaneously and scans at once.
FTIR works based on Michelson Interferometer which having
Beam splitter
Fixed mirror
Movable mirror

22. FTIR Instrumentation He-Ne gas laser Beam splitter Movable mirror
Light
source
He-Ne gas laser
Beam splitter
Movable mirror
Sample chamber
Fixed mirror
Detector
Interferometer

23. When the beams are combined an interference pattern is created
Combined beam reaches detector by passing through sample
Obtained spectrum is referred as Interferogram
This will be amplified and translated into IR spectrum by FTIR

24. Advantages Fast & sensitive All frequencies can be modulated at once
Simple mechanical design with only one moving part
No stray light is involved
When using He-Ne laser as internal standard, no need of external calibration
Availability of easy sampling accessories
Air pollutants like CO, ethylene oxide etc. can be analysed

25. Conclusion
FTIR having significant advantages over Dispersive IR due to its fast and accurate analysis.

26. References
Instrumental Methods Of Chemical Analysis; By Gurudeep R. Chatwal, pg No
Infra Red Spectroscopy: Fundamentals And Applications; By Barbara Stuart, pg No
Introduction to Spectroscopy, 4th edition, By Pavia, Lampman, Kriz.
Elementary organic chemistry, By Y.R.Sharma; 2007,Pg No