IR and FT-IR Spectroscopy

IR Spectroscopy

1. 1
IR and FT-IR
Presented By,
Chetan M. Jain
First Year M.Pharm
(Quality Assurance)
Government College of Pharmacy,Amravati.
11/12/16

2. InFRaRed
SpecTRoScopy
Intoroduction
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Provide useful information about structure of molecule.
Absorption of IR radiation by molecule and exhibit absorption
spectra.
Change in dipole moment.
Energy of radiation is directly proportional to wave number and
inversely proportional to wavelength.
RegionWavelength (µ) Wave number (cm
-1
)
Near IR 0.75-2.5 1200-4000
Infrared 2.5-16 4000-625
Far IR 16-200 625-10 11/12/16
Chetan Jain

3. oRIgIn oF IR SpecTRa
UV- Visible spectrum results in changes of electronic as
well as vibrational and rotational level in molecule.
IR radiation shows only vibrational and rotational level.
Vibrational-Rotational spectrum.
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4. 4
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5. InSTRumenTaTIon
The optical components of IR spectrophotometer are
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Light Source
Monochromator
Sample Holder
Detector
Recorder
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Dispersive instruments
FT-IR instrument
Non-dispersive instruments

6. IR RadIaTIon SouRce
Hot bodies continuously emmitting radiation
Incandescent lamp
Nernst Glover
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A closed wound nichrome wire is used.
A black oxide film formed on the coil gives emissivity by heating.
Temp. can be raised to 1100°C.
Used in near IR region and failed in IR region.
In IR region – most common source.
Consists of hollow rod-2mm in dia and 2-5cm in length.
Composed of mixture of oxides like zirconium, yttrium and thorium.
Temp: 1000-1800°C.
11/12/16Chetan Jain

7. Advantages of Nernst glower
Disadvantage
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It emits IR radiation over wide range of wavelength.
The intensity of radiation maintains steady and constant over long period
of time.
Used in air as it is not oxidized.
Frequent mechanical failure.
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8. Globar Source
Mercury Arc
Tungsten Filament lamp
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It is rod of sintered silicon carbide about 5cm in length and 4mm in
diameter
Temp- 1300°C.
 If radiation above 10µ it is used.
Far IR region it is used.
It is encolosed in quartz jacket to reduce loss.
Useful for near IR region only.
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9. MonochroMators
Select desired frequencies and reject other frequencies.
These are of two types
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1)Prism Monochromator
2)Grating Monochromator
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10. PrisM
MonochroMator
Greater range and simplicity.
Halogens salts are used.
Crystalline NaCl: 5-15µ
Crystalline KBr/CBr: 15-40 µ
LiF : 0.75-2.5
Two types
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Single beam monochromator
Double beam Monochromator
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11. GratinG MonochroMators
Series of parallel straight lines cut into plane
surface.
Constructed from glass coated with aluminium.
Gives radiation into single order.
Advantages
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Not attacked by moisture.
Used over considerable wavelength.
Sturdy and long lasting.
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12. saMPle holders and saMPlinG
of substance
Used for solid, liquid and gas.
Material containing sample must be transperent to
IR region.
Sample cell constructed from rock salt.
Sample must be pure and free from water.
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13. saMPlinG of solids
Solid dissolved in solvent
As Solid Film
Mull technique
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Carbon tetrachloride,Chloroform,acetone and cyclohexane.
Sample solution is placed on surface of KBr or Nacl and
allowed to evaporate.
Solid sample mixed with nujol to form a paste. This paste is
then sandwiched between two salt plates and used for spectral
measurement.
Nujol has absorption at 2915,1462,1376 and 719cm
-1
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14. Pressed Pellet Technique(Disk Method)
Advatages of pellet tech. over mull tech. is
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The small amount of finally ground solid sample is mixed with
100 times its weight of powdered KBr.
This mixture is pressed under high pressure in IR tablet press
to form pellet.
Eliminates the problem of band
If KBr pellet is preserved can be reused
Resolution of KBr is superior
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15. saMPlinG of liquids
For sampling of various cell like sandwitch cell,demountable cell
and cavity cell are used.
Made up of Nacl, KBr or thallium bromide.
Demountable cell:
Cavity cell:
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It consists of pair of salt plates separeted by gasket made of
metal or teflon and together by an clamp.
Matching a parallel-sided hole in a salt block makes it.
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16. saMPlinG of Gas
The dried gases introduced via a stop cock.
The gas sample is introduced into the gas cell made up of
glass or metal cylinder of about 10cm long.
The end walls of the gas cell made up of NaCl.
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17. Detectors
Two types of detectors are used
Thermal detectors
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Thermal detectors
Photodetectors
When IR radiation falls on these detectors they cause heating
which give rise to P.D. This P.D. is depends upon amt of
radiation.
Thermocouple
Bolometer
Thermister
Golay cell 11/12/16Chetan Jain

18. Thermocouple
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These are dissimilar strips of metal join together at one end.
Two fine wires of metals are welded with blackened gold foil,
which absorbs radiation.
One welded joint(Cold junction) is kept at constant temp.
The other welded joint (Hot junction) is exposed to radiation.
This exposure of hot junction causes rise in its temp, cause the
P.D. proportional to the amt of radiation.
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19. Bolometers
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These are constructed from metals or semiconductors.
When IR radiation falls on bolometer its temp. changes cause
change in the resistence of the conductor.
This change in the resistence of conductor is depends upon amt
of radiation.
This made one arm of Wheistone Bridge.
If IR radiation falls on the bolometer, the bridge becomes
unbalanced due to change in the electrical resistence causes
current flow through galvanometer.this amt of current flow is a
measure of intensity of radiation.
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20. Thermister
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These function similar to bolometer.
These are the resisters made by fusing several metallic
oxides.
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21. Golay cell
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It consists of metal cylinder.
One end of which closed by balanced metal plate and other with
metalised diaphragm.
Cylinder is filled with gas like xenon.
When the radiation falls on blackened metal plate it is heated which
causes expansion of gas, which affect the motion of diaphragm.
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22. Photon Detectors
Used in near IR region.
Consists of semiconductors like lead sulphide, lead
telluride.
When radiation are fall on these they goes to higher
level and produce signal.
Photoconductivity cell
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It consists of thin layer of lead sulphide supported on glass
and enclosed into an evacuated glass envelope.
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23. Fourier transForm ir
sPectroscoPy (Ftir)
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24. Fourier Transform IR
Spectroscopy (FTIR)
Advanced technique.
Interferometer(Michelson Interferometer).
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25. Advantages
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Fellgett Advantage
Jacquinot advantage
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26. InterpretatIon of Ir Spectra
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27. applIcatIonS of Ir and ft-
Ir
Qualitative application
Quantitative application.
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28. References
Pharamceutical analysis by A.V. Kasture, S.G. Wadodkar,K.R.
Mahadik, H.N. More, Volume II, Nirali Prakashan, Eleventh
edition (2004), p.no. 207-221.
Fundamental of analytical chemistry by D.A.Skoog,
D.M.West,F.J.Holler,7
th
edition p.no.592-597.
Organic Spectroscopy by William Kemp, 3
rd
edition, Palgrave
Publication, p.no19-56.
Instrumental Methods of Analysis by H.A.Willard, L.L.Merritt,
J.A.Dean, F.A. Settle, 7
th
edition, p.no. 288 to 320.
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