This document provides an overview of infrared spectroscopy. It discusses the electromagnetic spectrum and how infrared spectroscopy uses infrared light to analyze chemical bonds in molecules based on their vibrational and rotational frequencies. Different sampling techniques are described for analyzing powders, liquids, and gases. Key points covered include the principles of infrared absorption, molecular vibrations, Hooke's law application to frequency determination, and methods for preparing samples like KBr pellets and diffuse reflectance.

1. INFRARED
SPECTROSCOPY
Presented by
Navaneethakrishnan P
Department of Pharmaceutics
Karpagam College of Pharmacy
Coimbatore -32

2. CONTENT
• INTRODUCTION
• THEORY
• SAMPLING TECHNIQUES IN IR SPECTROSCOPY
• DISPERSIVE SPECTROSCOPY
2Department of Pharmaceutics, KCP, CBE-32

3. INTRODUCTION
• Infrared Spectroscopy is spectroscopic analytical method that deals
with the Infra-red Region of the electromagnetic Spectrum.
• By Using the IR can determine the chemical molecules
• In a laboratory Fourier Transform Infra-red spectrometer is used
• The Infra-red portion is usually divided into three regions
S.No IR Portion Wavelength in cm-1
1. Near Infrared 14,000 cm-1 to 4000 cm-1 (0.8 μm to 2.5 μm )
2. Mid Infrared 4000cm-1 to 400 cm-1 (2.5μm to 25 μm )
3. Far Infrared 400cm-1 to 10 cm-1 (25 μm to 1000 μm)
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4. ELECTROMAGNETIC SPECTRUM
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5. THEORY
• The EM radiation is a combination of periodically changing or
oscillating electric field (EF) and magnetic field (MF) oscillating at the
same frequency, but perpendicular to the electrical field.
• The wavelength is represented by λ
• The frequency is represented by v is a number of oscillation per unit
time of EM waves per sec.
• The wave number is number of waves / unit length
• So it can be given as
C =hv
C = Velocity of light 3,00,000 Km/s
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6. Cont....
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7. Cont..
• The wavelength (λ) is inversely proportional to the frequency (1/v)
• The energy in Quantum terms is given by Planks Constant equation,
E=hv or v =E/h
• Which was deduced later by Einstein, where E is the energy of the
Photon of frequency v and h is max Planks constant (h=4.13566 ×10-15
ev) wave and frequency are related by the equation
V = cv’
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8. Cont....
• The EM Spectrum can be divided several region in frequency or
wavelength. The relationship Between the frequency and wavelength
and the speed light is given below
v = c/λ
v = E/h
Hv = E
E = hc / λ
• Energy of IR is directly proportional to velocity of light and
inversely proportional to wavelength
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9. Cont...
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10. Molecular Vibrational
• The IR energy absorption corresponds to specific modes ; It
corresponding to combination of atomic movements.
• Vibrational force are two type
• BENDING VIBRATIONAL FORCE [change in bond angles]
• Scissoring
• Wagging
• Rocking
• Twisting
• STRETCHING VIBRATIONAL FORCE [Change in bond length]
• Symmetrical & Asymmetrical
• It corresponds to vibrational and rotational force
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11. Stretching
In the symmetrical
Stretching, atoms move
away from centres or
towards centre.
In Asymmetric Stretching,
some bonds are getting
shorter at the same time as
others are getting longer.
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12. Bending Vibration
Scissoring is
the movement
of two atoms
toward and
away from each
other.
Wagging is
like the motion
in which you
make a "V" sign
with your
fingers and
bend them
back and forth
from your wrist
Rocking is like
the motion of a
pendulum on a
clock, but an
atom is the
pendulum and
there are two
instead of one.
Twisting is a
motion as if the
atoms were
walking on a
treadmill.
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13. HOOKE's LAW
• Definition
Hooke’s law is a law of physics that states that the force needed to extend or
compress spring by some distance
• In Infrared spectroscopy, Hooke’s law is applied to determine the
molecules based on the peak range
• A vibrating bond in the IR can be compared to the physical model of a
vibrating spring system that can be described Hooke’s law of
harmonic oscillation.
• Using the force constant K and masses of two atoms M, then the
absorption should change as the properties of the system
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14. • In physics Hooke’s law used to determine force of spring
• Note : This is for understanding purpose
Cont...
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15. Cont ....
• In Infrared spectroscopy, Hooke's law is applied to determine the
vibrational stretching of atoms
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16. Cont...
• Hooke’s law given as
Where K is force constant (dynes /cm) ie bond strength
C = velocity of light
µ = m1 m2 / m1 + m2 ( where m is mass of atom )
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17. Determination of %Transmission
• Hooke’s law used in the determine the frequency required to stretch
the molecules
• Example:
The frequency required to stretch the C – H bond can be
calculated by using the Hooke’s formula.
k = 5x105 dyne/cm
m1 = C = 12/6.02x1023 = 1.99x10-23 g
m2 = H = 1/6.02x1023 = 0.167x10-23 g
c = 3x1010 cm/sec
Single bond = 5x105 dyne/cm
Double bond = 10x105 dyne/cm
Triple bond = 15x105 dyne/cm
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18. Cont...
The % Transmission of C – H is 3023 cm-1
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19. Sampling Techniques
Sampling of
Powders
Sampling of
liquid
Sampling of
Gas sample
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20. Sampling technique for Powders Sample
• Infrared spectroscopy incorporate several type of measurement
method like Diffuse reflectance method and attenuated total
reflection method
• The methods are selected according to sample form
• The KBr Method and Nujol method is classical method. How ever in
FTIR has become more common, The diffuse reflection method has
become more common and its widely used.
• The attenuated total reflection is method that allows direct
measurement of powder sample
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21. Cont....
The following methods are analysis the powder sample
• KBr Pellets method
• Nujol Method
• Diffuse Reflection Method
• Attenuated Total Reflection
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22. KBr Pellets method
• KBr Pellets Method:
• Alkali Halides are used in this method because it form a
transparent sheet when it is subject high pressure and this
transparent pellets allow the IR.
• KBr is the commonest alkali halide used in the pellets.
Cesium Iodide may be used to measure the lR region of 400
to 250 cm-1 wave number region
22Department of Pharmaceutics, KCP, CBE-32

23. Preparation Procedure
The size of pellets is
13mm in diameter
0.1 to 1.0% sample is
well mixes into 200 to
250mg fine KBr
The mixture is
pulverized and passed
into 200 mesh sieve
and dry at 100° C for
2 – 3 hours
The mixture is
compressed into
pellets
The compressional
force approx 8 tons is
applied under vacuum
for several minutes to
form a transparent
pellets
Degassing is applied
to remove all the air
and moisture
Inadequate vacuum
results is breaking and
scatter of IR
When measuring
background can be
measured with an
empty pellets without
sample and the only
analysis the pellets
containing sample
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24. Cont..
Appearance of MHP-1 Pelletizer
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25. Cont..
Appearance of KBr Pellets
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26. Cont..
Appearance of KBr Pellets
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27. Diffuse Reflectance Method
• Some IR are undergoes specular reflection at the powder surface and other light enter into sample at the
surface of the powder and and reappear after repeated transmission and reflection.
• In this Spectrum is obtained from diffuse reflected light
• Procedure
KBr powder are measured first (without sample)
0.1 to 10% of KBr Powder are diluted with sample 5 to 10 ng and it is packed into micro cup
Measure under IR
Advantage
• Little sample only required
• No need to form pellets
• Fast and easy cleanup
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28. Pulverized
the sample
and 1g of
sample is
taken
To this add
one or two
drops of
liquid
paraffin
Mix to
distribute a
sample in
liquid
paraffin
Apply the
Paste to
Liquid cell
Measure
with IR
Note : Since
liquid paraffin
exhibit spectra
3000 ,2800,
1460, 1375,
730 cm-1
Nujol Method
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29. Attenuated Total Reflection
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30. •This method is used to measure the IR spectra of sample is KBr or in
Liquid paraffin
•In this method the sample is pressed against the High reflective index
prism (It made up of Zinc selenide or Germanium)
•A Sample is mixed with KBr / liquid paraffin, and background data
collected without sample and then sample along KBr is analysed.
Advantages
•Faster Sampling
• Improving sample to sample reproducibility
• Minimize the spectral variation
Cont...
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31. Sampling Method for Liquid Sample
• The liquid samples are measured by transmission method.
• In the transmission method two types of cells are commonly
used
1. Liquid Cell
2. Fixed Cell
31Department of Pharmaceutics, KCP, CBE-32

32. •In the liquid cell, the sample droplets are placed on to the sodium
chloride or potassium bromide the appitude plate and sandwich in a
under another appitude plate such that no gas bubbles are trapped.
•The thickness is adjusted according to sample by using the screws.
•It is demountable sales or disassemble
•This is very useful to measuring the high viscous liquid an unsuitable for
low boiling point
Liquid Cell
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33. Liquid Cell
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34. Cont...
Components of
Liquids Cell
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35. •The fixed cell are used to measure a volatile sample
or a solution dissolved in appropriate solvent
•The reason furious in stopper at the sample and let
others a sample introduction and extraction from
the cell and cell washing without this disassemble.
•It is leak free
•It is used for analyser volatile sample
•the appropriate thickness is above 0.1 mm
thickness
Fixed Cell
35Department of Pharmaceutics, KCP, CBE-32

36. Sampling Method for Gas Sample
• The Gas sample are analysed by using and gas cell.
• There are two types of gas cell.
• 5cm and 10cm Gas cell
• Each cell body is consist of Glass material
• End of the cell is covered with potassium bromide window it
allow infrared radiation.
• 5 cm cell capacity is 42 ml and 10cm gas cell capacity is 98ml
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37. Cont...
Schematic outline for
Gas sampling
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38. Cont...
10cm long Gas
cell
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39. INSTRUMENTATION
• In the IR spectroscopy there are two types of instruments are
most commonly used, they are
1.Dispersive Infrared Spectrscopy
2.Fourier transform IR spectra
39Department of Pharmaceutics, KCP, CBE-32

40. Dispersive Infrared Spectrscopy
• The Dispersive infrared spectroscopy it has two type
single and double beam spectroscopy
• In the single beam Spectrscopy reference standard
cannot be analysed
• But in the double beam spectroscopy both reference
sample and standard Sample are analysed.
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41. Radiation source
Nerst Glower
Nichrome Wire
Globar
Monochromater
Prism
Grating
Detectors
Bolometer
Thermocouple
Golay cell
Pyroelectric detectors
Components of IR Instruments
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42. Nerst glower :
• It was used to provide a continuous source of IR radiation i.e near IR
• It Is Composed of
• Zirconium oxide 90% w/w
• Yttrium oxide 7% w/w
• Erbium oxide 3% w/w
• When it is heated electrically at the temperature of 2300°K (2026°C)
Radiation source
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43. 43Department of Pharmaceutics, KCP, CBE-32

44. Nichrome Wire:
• Nichrome is consist of Nickel
– Chromium wire
• It is 10 cm long wire
• When it is heated 1100°C it
can emita IR radiation ( Near
IR)
Radiation source
44Department of Pharmaceutics, KCP, CBE-32

45. GloBar:
• Globar is made up of Silicon Carbide
• It is 20-50mm in length and 5-10mm width
• It is heated by Electrically
• The silicon carbide rod is heated to temperature 1000°C to 1650°C
• Interference filter to produce a radiation between 4 to 15 micrometre
Radiation source
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46. Prism and Differential Grating:
• In traditional IR instruments monochromator are construct with Nacl or KBr Prism but
disadvantages of Prism is hygroscopic in Nature.
• For these reasons prism are not used instead of that diffraction grating have used
• Grating provide a Higher resolution power than Prism
• Even so most of grating operate automatically change around IR 2000 cm
Monochromator
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47. Working - Double beam IR Spectra
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48. Bolometer
•Bolometer are detectors used to measure the
Infrared Radiation
•They are very sensitive to thermal radiation
and are predominantly used in IR spectra
between 10 to 5000 micrometres
•Any thermal radiation that impinges upon the
detector will cause a temperature change. This
will cause change in resistance which is
amplified and measured as a voltage difference
Detectors
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49. Fields of application:
• Aerospace/astronomy
• Defense and security
• Firefighting
• Inspection/maintenance
• Laser beam profiling
• Medical
• Night vision
• Remote sensing
• Search and rescue
• Transportation
Detectors
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50. Thermocouple
•The thermocouple is made by welding
together of a two wires of metal 1 and
2
•The metals are Bismuth and antimony
•There are two junction hot junction
and cold junction.
•The IR radiation falls on hot zone and
the potential difference between the
hot and constant temperature zone is
measured and sent to amplifier.
Detectors
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51. Detectors
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Thermocouple Applications
Some of the applications of thermocouple include the
following.
•These are used as the temperature sensors in
thermostats in offices, homes, offices & businesses.
•These are used in industries for monitoring
temperatures of metals in iron, aluminum, and
metal.
•These are used in the food industry for cryogenic
and Low-temperature applications. Thermocouples
are used as a heat pump for performing
thermoelectric cooling.
•These are used to test temperature in the
chemical plants, petroleum plants.
•These are used in gas machines for detecting the
pilot flame

52. Golay cell
• The glow cell is a type of detector mainly used for
IR spectra
• It is consisting of gas field and closure with an
infrared absorbing material and a flexible diagram
or membrane
• When IR radiation is observed it heat the gas
causing to expand the membrane
• The resulting increasing in pressure deforms the
membrane and these reforms in the membrane
will be changes in the signal on photodiode
resulting increasing in pressure reforms than
membrane and these reforms in the membrane
will be changes engine signal on photodiode
Detectors
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53. 1. Infrared spectroscopy https://www.ru.nl/systemschemistry/equipment/optical-
spectroscopy/infrared/
2. Vogel’s Text book of Quantitative chemical analysis by Jerrfy et.al
3. Infrared Spectroscopy theory and Interpretation of IR https://slideplayer.com/slide/8335494/
4. Fundamental of IR spectroscopy https://www.shimadzu.com/an/ftir/support/ftirtalk/index.html
5. Attenuated total reflection sampling
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.utsc.utoronto.ca/~traceslab/
ATR_FTIR.pdf&ved=2ahUKEwirjobmuujfAhUVAXIKHefqD5YQFjAZegQIAxAB&usg=AOvVaw1p-7DG-
txypQxhy1wqJSQq&cshid=1547303582941
6. Practical Sampling Techniques for Infrared Analysis edited by Patricia B. Coleman
https://books.google.co.in/books?hl=en&lr=&id=JY_H61INJqMC&oi=fnd&pg=PA2&dq=sample+handli
ng+techniques+infrared+spectroscopy&ots=DCbrdbqsy2&sig=KkZdnDxPzvitsd4lF14pGlzhA6w#v=onep
age&q=sample%20handling%20techniques%20infrared%20spectroscopy&f=false
7. Introduction to Infrared Spectroscopy April 2012, Research gate
https://www.researchgate.net/publication/224831013
Reference
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54. 7. FT-IR vs. Dispersive Infrare Theory of Infrared Spectroscopy Instrumentation
https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.thermo.com.cn/Resou
rces/200802/productPDF_21615.pdf&ved=2ahUKEwj8qPnNkevfAhUErI8KHUerBjYQFjAAegQIA
xAB&usg=AOvVaw2oR7zNrc-XIvb4HibRdXjc
8. Near Infrared Spectroscopy: fundamentals, practical aspects and analytical applications ,
Journal of the Brazilian Chemical Society vol 14 Sau paul April 2003
http://www.scielo.br/scielo.php?pid=S0103-50532003000200006&script=sci_arttext
9. Application of Non-Dispersive Infrared (NDIR) Spectroscopy to the Measurement of
Atmospheric Trace gases
https://www.google.com/url?sa=t&source=web&rct=j&url=https://ir.canterbury.ac.nz/bitstrea
m/handle/10092/2160/Thesis_fulltext.pdf%3Bsequence%3D1&ved=2ahUKEwj6zP7uherfAhXFL
48KHWOLCIsQFjATegQIAhAB&usg=AOvVaw06IQX-ysQupfLLm0HLASCZ
10. Monochromator
https://www.shimadzu.com/an/uv/support/fundamentals/monochromators.html
11. Golay cell https://en.m.wikipedia.org/wiki/Golay_cell
Reference
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55. Reference
12. Pyroelectric Detector https://www.infratec.in/sensor-division/service-
support/glossary/pyroelectric-detector/
13. Thermal detector https://www.slideshare.net/mobile/sampathramaswamy1/thermal-
detectors-of-ir
14. Introduction and calculations of IR https://www.chromacademy.com/lms/sco533/06-
infrared-spectroscopy-calculation-molecular-vibrations.html
15. Hand book of thermal detector Chapter 7
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.hamamatsu.
com/resources/pdf/ssd/e07_handbook_Thermal_detectors.pdf&ved=2ahUKEwi1gc7Y
k-vfAhWGNY8KHYQaAnkQFjAAegQIBRAB&usg=AOvVaw0NY1YMZO7MkrCMtm3-Gzek
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56. 56Department of Pharmaceutics, KCP, CBE-32