Molecular vibrations cause characteristic absorption bands in the infrared region of the electromagnetic spectrum. [FTIR] spectroscopy involves passing infrared radiation through a sample and measuring the wavelengths absorbed. This creates a molecular "fingerprint" that can be used to identify unknown chemicals and study molecular structure. FTIR has numerous applications including analysis of organic materials, biological samples, and industrial contaminants. It provides a simple, rapid and sensitive technique for analytical chemistry.

2. WHAT DO U MEAN BY ANALYTIC
TECHNIQUES??
 1.Separation techniques →Chromatography
 2.Spectrophotometric → Spectroscopy
 3. Electro analytical → Potentiometry,
Conductometry
 4. Titrimetric analysis→ Titrations

3. WHAT? WHY?

4.  Spectroscopy is the branch of science.
 Deals with the study of interaction of
electromagnetic radiation with matter.
WHAT ARE ELECTROMAGNETIC
RADIATIONS??
 Electromagnetic radiation - a type of energy that
is transmitted through space at enormous
velocities.

5. • measures the amount of light that is absorbed by
the solution in a cuvette placed in the
spectrophotometer.

6. Around 1800, Herschel studied
the spectrum of sunlight using
the prism. He measured the
temperature of each color, and
found the highest temperature
was just beyond the red, what
now we call the ‘infrared’.
DEVELOPMENTAL BACKGROUND
SIR FRIEDRICH WILLIAM
HERSCHEL first discovered
infra red spectrophotometry.

8. WHAT IS AN INFRARED REGION??
 The infrared region of the spectrum
encompasses radiation with wave lengths ranging
from 0.8 to 2µ.
Infrared region lies between visible and microwave
region.

9. IR region: 0.8 µm (800nm) to 2000 µm (2mm)
1. Near IR: 0.8-2 µm
2. Middle IR: 2-15 µm
3. Far IR: 15-2000 µm
Sub divided into

10. Most organic spectroscopy uses electromagnetic energy, or radiation,
as the physical stimulus.
Other types of radiation such as alpha rays, which consist of helium
nuclei, have a detectable mass component and therefore cannot be
categorized as electromagnetic energy.
The important parameters associated with electromagnetic radiation are:
• Energy (E): Energy is directly proportional to frequency, and inversely
proportional to wavelength, as indicated by the equation below.
• Frequency (m)
• Wavelength (l)
E = hm

11. Sunlight provides an irradiance of just over
1 kilowatts per square meter at sea level. Of
this energy, 527 watts is infrared radiation,
445 watts is visible light, and 32 watts is
ultraviolet radiation.

12.  Rapid continuous and batch analysis of
compound in fermentation broth can be studied.
 VACCARI et.al., (1994) had used technique to
measure glucose and lactic acid biomass
fermentation.
 Used to estimate techoic acid in membranes and
antibiotics.

13. IR spectroscopy is concerned with the study of
absorption of infrared radiation, which causes
vibrational transition in the molecule.
Hence, IR spectroscopy also known as Vibrational
spectroscopy.

14. INFRARED
SPECTROMETER

16. VIBRATION
MODE
Stretching
Change in intra-atomic
distance,bond angle remain
same
Symmetr
ic
Asymmetri
c
Bending
Change in bond angle
intra atomic distance
remain same
In plane
Scissoring Rocking
Out of
plane
Wagging Twisting
16
MOLECULAR VIBRATIONS

19. Physical
stimulus
Molecule response Detecting
instrument
Visual (most common)
representation, or
Spectrum
HOW TO OBTAIN A SPECTRUM??

20. 1. Recognize a pattern.
2. Associate patterns with physical parameters.
3. Identify possible meanings, i.e. propose
explanations.

21. The main challenge:
 To extract the information it contains in
abstract, or hidden form.
 Requires the recognition of certain
patterns,
› The association of these patterns with
physical parameters,
› The interpretation of these patterns in terms
of meaningful and logical explanations.

22. Based upon the simple fact that
A chemical substance shows selective absorption in
the infrared region.
After absorption of IR radiation, the molecules of a
chemical substance vibrate at many rates of vibration.
Give rise an IR absorption spectrum.
Various bands present corresponds to the characteristic
functional groups and bonds present in a chemical
substance.
IR spectrum is a fingerprint for its identification.

23. › characterized by the handling of the IR frequencies
 1) dispersive type
 2) interferometric type
› Characterised by the source
 1)single beam IR spectrometry
 2)double beam IR spectrometry

24.  In dispersive type the infrared light is separated
into individual frequencies by dispersion, using a
grating monochromator.
 In interferometric type the frequencies
are allowed to interact to produce an
interference pattern and this pattern is then
analyzed, to determine individual frequencies
and their intensities.

25.  Radiation is emitted by the source through a
fixed prism and a rotating mirror.
 It select the desired wavelength and then allow it
pass on to the detector.
 The detector measures the intensity of radiation
after it passes through the sample.
 Knowing the original intensity of radiation ,one
can measures the degree of wavelength
› the absoption spectrum of the sample can be obtained.

26. The various disadvantages of single beam
spectrophotometry:
 the intensity of the emission radiation source varies from
point in IR absoption spectrum;
 Therefore ,the resulting spectrum is considerably
deformed.
 The necessary correction by the continuous variation of
slit is cumbersome.

27.  The radiation is divided into two beams ,
› one of which passes through the sample
› while the other function as a reference beam.
 They are passed in alternate into a Monochromator at
very short intervals by means of a rotating mirror.
 The information from this beam is rationed to obtain
the required sample spectrum.

29.  The main parts of an IR spectrometer are as
follows
 1) IR radiation source
 2) Monochromators
 3) Sample cells
 4) Detectors

30. INFRARED SOURCES
 a) Nernst glower or Nernst filament: they are
made up of sintered mixtures of oxides of Zr, Th,
Ce, Y, Er, etc.
› Used in near IR region.
› Intensity of radiation produced is more intense.
› Used for detection of carbohydrates & proteins.
 b) globar source: made up of silicon carbide.
They are self starters.
used in middle IR region.
used to detect simple functional
groups.

31.  C) incandescent lamp: it is made up of
nichrome wire.
used in near IR
instruments.
Has a low spectral
emissivity.
It is heated up to 1100K.
Used to detect complex organic
molecules
 d) mercury arc: high pressures are used.
used in far IR region.
intensity of radiation is
greater.
used to detect inorganic
complexes.

32.  e) tungsten lamp: they heated up to 3500K
used in mid IR region.
intensity of radiation is mild.
used to detection of organic
functional groups
MONOCHROMATORS
• They convert polychromatic light into mono
chromatic light.
• They must be constructed of materials which
transmit the IR.
• They are of 3 types.
• a) metal halide prisms
• b) NaCl prisms
• c) gratings

33.  a) metal halide prisms:
 prisms which are made up of KBr are used in
the wavelength region from 12-25µm.
 LiF prisms are used in the wavelength region
from 0.2-6µm.
 CeBr prisms used in wavelength region from
15-38µm.
 b) NaCl prisms:
 Used in the whole wave length region from
4000-650cm-1.
 they have to be protected above 20•c
because of hygroscopic nature.
 c) gratings:
• They offer better resolution at low frequency than prisms.

34. SAMPLE CELLS
 Sample cells made up of alkali halides like
NaCl or KBr are used.
 Aqueous solvents cannot be used as they
dissolve alkali halides.
 Only organic solvents like chloroform is
used.
 IR spectroscopy has been used for the
characterization of solid, liquid, gas samples.

35. Detectors
• They convert the radiation into electrical signal.
• There are mainly 5 types of detectors used in IR.
 Thermo couple detectors:
• made up of bismuth& antimony coated
by metal oxides.
• material thermally
active.
used in dispersive instruments.
• Response time is 30 seconds.
• They give responses for all frequencies.

36.  These are made up of sintered oxides
of Mn, Co, Ni.
• The material sh0uld be thermally
sensitive.
• The response time is 4 seconds.
Pyro electric detectors
• These are made up of TGS, LiTaO3.
• They are used in FTIR instruments.
• It involves multiple scanning.
.

37.  The material used is CO2.
 The material should be
inert in nature.
• used in non dispersive IR
instruments.
• Response time is 0.01 sec.

38.  comprise a film of semiconducting material
deposited on a glass surface, sealed in an
evacuated envelope.
 These detectors have better response
characteristics than pyroelectric detectors
 Used in FT-IR instruments - particularly in
GC - FT-IR.

39.  Molecules are made up of atoms linked by chemical
bonds.
 The movement of atoms and the chemical bonds like
spring and balls (vibration)
 This characteristic vibration are called Natural
frequency of vibration.

40. When energy in the form of infrared radiation is applied
then it causes the vibration between the atoms of the
molecules and when
Applied infrared frequency = Natural frequency of
vibration
Then, Absorption of IR radiation takes place and a peak is
observed.
Different functional groups absorb characteristic
frequencies of IR radiation. Hence the characteristic
peak value.
Therefore, IR spectrum of a chemical substance is a finger
print of a molecule for its identification.

41. IR bands can be classified as strong (s), medium (m), or weak (w),
depending on their relative intensities in the infrared spectrum. A strong
band covers most of the y-axis.

52.  FT-IR stands for Fourier Transform Infra Red,
› the preferred method of infrared spectroscopy.
 In here IR radiation is passed through a sample
 Some of the infrared radiation is absorbed by the sample and
some of it is passed through (transmitted).
 The resulting spectrum represents the molecular absorption and
transmission, creating a molecular fingerprint of the sample.

53.  No two unique molecular structures produce
the same infrared spectrum.
 Useful for several types of analysis.

55. ADVANTAGES
– FTIR is a simple and sensitive analytical tool.
– Provide fast data acquisition tool.
– Simple to operate
– Most useful analytical tool
• To determine the composition of organic materials
• To identify IR transparent or semi-transparent
inorganic films
• Provides quantitative determination of compounds
in mixtures

56. Dispersive Spectrometer FTIR
In order to measure an IR
spectrum
It takes several minutes
The detector receives only a
few % of the energy of original
light source.
In order to measure an IR
spectrum
FTIR takes only a few
seconds
The detector receives up to
50% of the energy of original
light source (much larger than
the dispersion spectrometer )

57.  Identification of Substances
 The “Fingerprint” Region (1200 to 700 cm-1): To
identify an unknown compound.
 Determination of Molecular Structure
 Studying Progress of Reactions
 Analysis of Petroleum HCs, Oil & Grease contents
 Shape of Symmetry of a Molecule
 Identification of Functional Groups
 Presence of Water in Sample
 Measurement of Paints & Varnishes

58. BIOLOGICALAPPLICATIONS
 Characterization of isolated biological molecules,
particularly proteins and lipids.
 Studies of more complex systems, such as diseased
tissues.
 Analysis of blood serum to determine the relative
amounts of lipid present.
 Study structures of membrane proteins, Study the
secondary structures of proteins
 Myelin basic protein (MBP) is a major protein of the
nervous system and has been studied by using FTIR
spectroscopy

59.  Study protein adsorption onto surfaces.
 The nucleic acids, deoxyribonucleic acid (DNA)
and ribonucleic acid (RNA), may be studied.
 The pressure-dependence on parameters such as
wave number, intensity and band shape may
provide information about the structural changes
associated with malignancy.
 For characterizing and differentiating microbial
cells.

60.  FTIR spectroscopy provides a rapid method for
identifying micro-organisms responsible for
infections.
 Hierarchical cluster analysis of many microbes
can be done.
 For the investigation of plant materials.
 Glucose, blood and urine analyses.

61.  Determination of unknown contaminants in
industry using FTIR.
 Determination of cell walls of mutant & wild type
plant varieties using FTIR.
 Biomedical studies of human hair to identify disease
states (recent approach).
 Identify odour & taste components of food.
 Determine atmospheric pollutants from
atmosphere itself.

62. Place:
Periyar university, Salem
PSG college of arts and sciences ,Kovai,
Bharathidasan unveristy, Coimbatore
Sitra,Coimbatore
Sastra university, Tanjore,
IIT saif, Madras
SAIF-STIC Kerala
CEPC, Kerala
Instrumentation fee:
100 to 500 Rs
INSTRUMENTATIO
N

63.  Graphics source: Wade, Jr., L.G. Organic Chemistry, 5th ed. Pearson Education
Inc., 2003
 www.kinetics.nsc.ru/chichinin/books/spectroscopy/Stuart04.pdf
 http://www.digitalbookindex.org/_search/search010chemspectroscopya.asp
 http://www.acs.org
 http://www.cas.org
 http://www.chemcenter/org
 James Robinson, George Frame, Eileen Frame; instrumental analysis; sixth
edition
 James vargeese; Analytical Spectroscopy; first edition; 2010.
 https://www2.chemistry.msu.edu/faculty/reusch/.../InfraRed/infrared.htm