This document discusses infrared spectroscopy. It begins by explaining that infrared spectroscopy, also called vibrational spectroscopy, works by having molecules in a sample absorb infrared radiation. This causes the molecules to undergo transitions to different vibrational states. Each compound absorbs infrared radiation at different frequency regions, allowing for detection. The document then discusses various aspects of infrared spectroscopy including the electromagnetic spectrum regions, common uses, important terms, instrumentation, sample preparation techniques, and types of molecular vibrations that can be observed.

1. INFRARED SPECTROSCOPY
P.DEEPIKA
ASSISTANT PROFESSOR
Aditya bangalore institute of pharmacy education and resaerch
Dept. Of PHARMACEUTICAL ANALYSIS

2. PRINCIPLE
 Infrared spectroscopy is also called as “Vibrational
spectroscopy”.
 The molecules present in the sample solution absorbs IR
radiation particularly MID-IR radiation and undergoes
into different transitional states and leads to production
of vibrations.
 These vibrations occurs at different frequency region.
 Thereby the compound is detected.

3. Electromagnetic spectrum of IR can be divided into---
 NEAR IR --
 MID IR --
 FAR IR --
0.8µm-2.5µm
2.5µm-50µm
50µm-1000µm
*MID IR is the active region in which molecules tend to vibrate

4. USES OF IR SPECTROSCOPY
 Structural elucidation ( Det. Of functional group
present in a molecule)
 To find out which type of bond present in the
molecule i.e., single/double/triple bonds
 Or the group attached with these bonds can also be
known.

5. IMPORTANT EMS TERMS
 Wavelength
λ –lambda
 Frequency
ν- pnew
 Energy- E
 E=hν
ν Increases—E also increases

6.  Compounds which absorbs IR radiation
are...Organic compounds and Carbonmonoxide
 Compounds which doesnt absorbs IR radiation
are...
Hydrogen, Oxygen, Nitrogen

7. IR-SPECTRA
X-AXIS-
Wavenumbers (Frequency regions)
Lies in between 4000cm-1 to 400cm-1
Y-AXIS-
% Transmittance values
•If %T is 100%, it means NO
ABSORPTION has been taken place
in the molecule.
IO -------SAMPLE---------IT
Total transmittance (T)= IT / IO
%T=100* IT / IO
Where, IO is Intensity of incident light
and IT is Intensity of transmitted light

8. TYPES OF VIBRATIONS
Molecular vibration
divided
into
stretching bending
Involves
change in
bond length
involves
change in bond
angles
symmetrical asymmetrical
scissoring
rocking twisting
wagging
in-plane
vibration out of
plane
vibration8

9. INSTRUMENTATION (Dispersive IR)
1. IR SOURCE
2. SAMPLE COMPARTMENT
3. MONOCHROMATOR
4. DETECTOR
5. READOUT DEVICE
1 2 3 4

10. IR SOURCES
1. NERNST GLOWER:
 It is constructed with rare
earth oxides in the form of a
hollow cylinder.
 Platinum leads at the ends of
the cylinder permit the
passage of electricity.
 Nernst glowers are fragile.

11. 2. GLOBAR SOURCE:
 A globar is a rod of silicon carbide
(5 mm diameter, 50mm long)
which is electrically heated to about
1,500 K.
3.CARBON DIOXIDE LASER:
 Very rarely used becz its highly
expensive

12. MONOCHROMATOR
 A monochromator is a means of
separating wavelengths of the
source radiation.
 The monochromator is used to
separate polychromatic radiation
into a suitable monochromatic
form.
 This is achieved by means of
prisms or diffraction grating.

13.  High resolution prism
instruments contain
combination of Si02,
NaCl and KBr prisms.
 Low-cost instruments
use NaCl prisms

14. DETECTORS
1. Thermocouple detector
2. Thermistor
3. Pyroelectric detector
4. Photoelectric detectors
*Used to detect the compound or the species
THERMAL DETECTORS

15. 1.THERMOCOUPLE DETECTOR :
•Thermocouples consist of a pair of junctions of different metals two pieces of
bismuth fused to either end of a piece of antimony.
•The potential difference (voltage) between the junctions changes according to the
difference in temperature between the junctions

16. 2.PYROELECTRIC DETECTOR:
 Pyroelectric detectors are made
from a single crystalline wafer of
a pyroelectric material, such as
triglycerine sulphate (TGS).
 The properties of a pyroelectric
material are such that when an
electric field is applied across it,
electric polarisation occurs.

17. 3.BOLOMETER:
 A bolometer functions by
changing resistance when
heated.
 It is constructed of strips of
metals such as platinum or
nickel
4. PHOTOELECTRIC
DETECTORS:
 Madeup of mercury cadmium
telluride detector

18. SAMPLE PREPARATION TECHNIQUES
1. LIQUIDS
2. SOLIDS
 KBr pellet technique
 Mull technique
3. GASES

19. LIQUIDS:
 Pure or soluted in transparent solvent – not water (attacks
windows)
 The sample is most often in the form of liquid films
(“sandwiched” between two NaCl plates)
SOLIDS( KBr pellet technique):
 A milligram or less of the fine ground sample mixed with
about 100 mg of dry KBr powder in a mortar or ball mill.
 The mixture compressed in a die to form transparent disc.

20. SOLIDS(MULL TECHNIQUE):
 Grinding a few milligrams of the powdered sample with
a mortar or with pulverizing equipment.
 A few drops of the mineral oil added (grinding
continued to form a smooth paste).
 Nujol is used as mineral oil.(It is a heavy paraffin oil
so it is chemically inert.
 Composition of Nujol is heavy paraffin.
 And applied as a thin transparent film

22. THANK YOU