Instrumentation method of analysis topic Ir spectroscopy.

1. INFRA RED
SPECTROSCOPY
SUBMITTED TO :- AP. SHREYA ARORA
SUBMITTED BY:- RAHUL DOGRA
REG.NO.:-72313026
M.PHARMACY(1ST SEM.)

2. • INTRODUCTION
• PRINCIPLE
• TYPES OF VIBRATION
• FACTORS INFLUENCING VIBRATIONAL FREQUENCY
• INSTRUMENTATION
• APPLICATION OF IR SPECTROSCOPY
• LLIMITATION OF IR SPECTROSCOPY
CONTENT

3. • Infrared spectroscopy or vibrational spectroscopy is
concerned with the study of absorption of infrared
radiation, which results in vibrational transitions.
• Infrared radiations refers broadly to that part of
electromagnetic spectrum between visible and
microwave region.
INTRODUCTION

4. • When the frequency of the IR radiation is equal to
the natural frequency of vibration, the molecule
absorb IR radiation and a peak is absorbed.
•
• Every bond or portion of a molecule or functional
group requires different frequency for absorption.
PRINCIPLE

5. • IR radiation does not have enough energy to
induce electronic transitions as seen with UV.
• For a molecule to absorb IR, it must be
accompanied by a change in dipole moment.
• Regions of wavelength range
•
• There are three regions:
1. Very near IR: Overtone region(2-2.5μ)
2. Near IR: Vibration region(2.5-25µ)
3. Far IR Rotational region(25-400μ)
THEORY

7. ⚫ There are different types of vibrations:
1.Stretching
i. Symmetric
ii. Asymmetric
2. Bending
i. In-plane bending Scissoring
a. Scissoring
b. Rocking
ii. Out-of-plane bending
a. Wagging
b. Twisting
TYPES OF VIBRATIONS

9. 1. Symmetry
Symmetric compounds do not possess dipole moment
and are IR inactive.
E.g. symmetric acetylene
2. Fermi resonance
Fermi resonance results in an unexpected shift in energy
and intensity of the bands.
E.g. the overtone of C-H deformation mode at 1400 cm is
always in Fermi resonance with the stretch of the same
band at 2800 cm¹.
FACTORS AFFECTING VIBRATIONAL FREQUENCY

10. 3. Hydrogen bonding
Hydrogen bonding brings about remarkable downward
frequency shifts.
Intermolecular - broad bands
Intra-molecular-sharp bands
4. Electronic effect
Electronic effects such as inductive, mesomeric and field
effect may cause shift in absorption bands due to change
in absorption frequency.
E.g. Inductive-acetone(1715cm) and
chloroacetone(1725cm)
Mesomeric-acetophenone(1693cm) and p-amino
acetophenone(1677cm")

11. 5.Bond angles
Difference in bond angles also lead to the changes in
absorption bands.
E.g.

12. . The main parts of IR spectrometer are as follows:
1. IR radiation sources
2. Monochromators
3. Sample cells and sampling of substances
4. Detectors
INSTRUMENTATION

13. The radiation source must emit IR radiation which must
be
(i) intense enough for detection
(ii) steady
(iii) extend over the desired wavelengths
The various popular sources of IR radiations are :
(i) Incandescent lamp
(ii) Nernst glower
(iii) Globar Source
(iv) Mercury Arc
IR RADIATION SOURCES

14. They must produce intense & steady radiation.
RADIATION SOURCES

15. A. Prism:
Used as dispersive element.
Constructed of various metal halide salts.
Sodium chloride is most commonly prism salt used.
MONOCHROMATOR

16. Grating are nothing but rulings made on some materials
like glass, quartz or alkylhalides depending upon the
instrument. The mechanism is that diffraction produces
reinforcement. The rays which are incident upon the
gratings gets reinforced with the reflected rays.
GRATING

17. • Infrared spectra may be obtained for gases, liquids
or solids.
. Materials containing sample must be transparent to
the IR radiation. So, the salts like NaCI, KBr are only
used.
SAMPLE CELL &SAMPLING OF SUBSTANCE

18. Samples of the same substance shows shift in
absorption bands as we pass from solid to gases and
hence the samples of different phases have to be
treated differently in IR spectroscopy.
Sampling of solids
1. Solids run in solution
2. Mull technique
3. Pressed pellet technique
4. Solids films
SAMPLE HANDLING

19. 1. Solids run in solution.
Dissolve solid sample in non -aqueous solvent and place a
drop of this solution in alkali metal disc and allow to
evaporate, leaving a thin film which is then mounted on a
spectrometer.
E.g. of solvents-acetone, cyclohexane, chloroform etc.
2. Mull technique
Finely powdered sample + mulling agent (Nujol) and make
a thick paste (mull). Transfer the mull to the mull plates and
the plates are squeezed together to adjust the thickness it is
then mounted in spectrometer.

20. 3. Pressed pellet technique
Finely powdered sample is mixed with about 100 times its
weight of KBr in a vibrating ball mill and the mixture is
then pressed under very high pressure in a die to form a
small pellet (1-2mm thick and 1cm in diameter).

21. 4. Solid films
Here amorphous solid is dissolved in volatile solvents
and this solution is poured on a rock salt plate (NaCl
or KBr), then the solvent is evaporated by gentle
heating.

22. Liquids sample can be sandwiched between two
alkali halide plates (NaCl, KBr, CaF2). The sample
cell thickness is 0.01-0.05mm.
SAMPLING OF LIQUID

23. Here gases sample is introduced into a glass cell
made up of NaCl.
Very few organic compounds can be examined as
gases.
E.g. 1, 4-dioxane
SAMPLING OF GASES

24. . The detectors can be classified into three categories:
1. Thermal detectors:- Their responses depend
the heating effect of radiation.
2. Pyroelectric detectors:- Pyroelectric effect
depends on the rate of change of the detector
temperature rather than on the temperature itself.
3. Photoconducting detectors:- Most sensitive.
DETECTOR

26. • 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.
DISPERSIVE IR INSTRUMENT

27. • FTIR collects all wavelengths simultaneously and at
once.
•
• FTIR works based on Michelson Interferometer
which having
•
• (i) Beam splitter
•
• (ii) Fixed mirror
•
• (iii)Movable mirror
FOURIER TRANSFORM IR INSTRUMENT

28. FTIR INSTRUMENTATION

29. 1. Identification of an organic compound
To measure spectrums.
No two samples will have identical IR spectrum.
APPLICATION OF IR SPECTROSCOPY

30. ⚫ Absorption band in the region 1500-500 cm. ⚫ Useful for
establishing the identity of a compound.
It consists of:
1. Region 1500-1350 cm: Appearance of doublet near 1380
cm and 1365cm shows the presence of 3º butyl group.
2. Region 1350-1000 cm: All classes of compound
viz.alcohol, esters, lactones shows absorptions in the region
due to C-O stretching.
3. Region below 1000 cm: This region distinguishes between
cis and trans alkene.
FINGERPRINT REGION

31. • The presence or absence of absorption bands help in
predicting the presence of certain functional group in the
compound.
QUALITATIVE DETERMINATION OF FUNCTIONAL GROUP

32. It can be done by measuring the intensity of the
absorption bands.
This is done by baseline technique and is thus used to
determine the quantity of a substance.
QUANTITATIVE ANALYSIS

33. Impurities have different chemical nature when compared
to the pure drug.
. Hence these impurities give rise to additional peaks than
that of the pure drug.
By comparing these we can identify the presence of
impurities.
IDENTIFYING THE IMPURITIES IN DRUG SAMPLE

34. • By IR spectroscopy, it is not possible to know the
molecular weight of a substance.
•
• It does not provide information of the relative
positionsof different functional groups on a molecule.
•
• From a single IR spectrum of an unknown substance, it
is not possible to know whether it is a pure compound
or a mixture of compounds.
LIMITATION OF IR SPECTROSCOPY