Infrared Spectroscopy

1. INFRARED
SPECTROSCOPY
A
PRESENTATION
ON INFRARED SPECTROSCOPY
BY MS. SNEHA S. GHADIGAONKAR
M.PHARM (PHARMACEUTICAL QUAILITY
ASSURANCE)
DR. D.Y. PATIL COLLEGE OF PHARMACY, AKURDI.

2.  ELECTROMAGNETIC RADIATION
 IR SPECTROSCOPY
 RANGE OF INFRARED RADIATION
 REQUIREMENT FOR INFRARED RADIATION ABSORPTION
 INSTRUMENTATION
 MOLECULAR VIBRATIONS
 REGIONS OF IR SPECTRUM
 APPLICATIONS OF IR SPECTROSCOPY
 LIMITATIONS OF IR SPECTROSCOPY
 CASE STUDY
 REFERENCES
CONTENTS

3. ELECTROMAGNETIC RADIATION

4.  The technique is based upon the simple fact that a chemical substance
shows marked selective absorption in the infrared region.
 After absorption of IR radiations, the molecule of a chemical substance
vibrate at many rates of vibration, giving rise to the close-packed
absorption bands, called an IR absorption spectrum which may extend
over a wide wavelength range.
 Various bands will be present IR spectrum which will correspond to the
characteristic functional groups and bonds present in a chemical
substance.
 Thus an IR spectrum of a chemical substance is a fingerprint for its
identification.
IR SPECTROSCOPY OR
VIBRATIONAL SPECTROSCOPY

5.  The infrared portion of the electromagnetic spectrum is usually
divided into three regions;
 The higher-energy near-IR, approximately 14000–4000 cm−1
(0.7–2.5 μ ) can excite overtone or harmonic molecular vibrations.
 The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μ) may
be used to study the fundamental vibrations and associated
rotational-vibrational structure.
 The far-infrared, approximately 400–10 cm−1 (25–1000 μ), lying
adjacent to the microwave region, has low energy and may be used
for rotational spectroscopy
RANGE OF INFRARED RADIATION

6. CORRECT WAVELENGTH OF
RADIATION
ELECTRIC DIPOLE
REQUIREMENT FOR INFRARED
RADIATION ABSORPTION

7.  THERE ARE TWO TYPES OF INSTRUMENTS FOR INFRARED
ABSORPTION MEASUREMENTS AVAILABLE:
 dispersive grating spectrophotometers for qualitative measurements
 fourier transform infrared (ft-ir) instruments for both qualitative and
quantitative measurements.
 THE MAIN PARTS OF IR SPECTROMETER ARE AS FOLLOWS:
 radiation source
 monochromators
 sample cells and sampling of substances
 detectors
 recorder
INSTRUMENTATION

9.  IR instruments require a source of radiant energy which emit IR radiation
which must be of Sufficient intensity, Continuous, Stable.
SOURCES OF IR RADIATIONS ARE AS FOLLOWS:
 GLOBAR: Rod of silicon carbide Heated up to 1300 degree centigrade
Emits maximum radiation at5200cm
 NERNST GLOWER: Rod of zirconium and yittrium Heated up to 1800
degree centigrade Emits maximum radiation at about 7100cm
 MERCURY ARC: in the far infrared region the sourses described above
lose their effectiveness and special high pressure mercury arc lamp are
used
RADIATION SOURCE

10.  PRISM MONOCHROMATOR :
 The white light pass through a piece of glass and be divided into a rainbow spectrum.
Entrance slit allows source radiation to illuminate the first lens which collimates the light
spreading it across the face of the prism. Prism disperses radiation into component
wavelengths and the second lens focuses the spectrum at the focal plane. An exit slit selects
the band of radiation to reach the detector.
 GRATING MONOCHROMATOR:
 It is a device which consists of a series of parallel & closely spaced grooves rules on glass or
any reflecting surface
 GRATINGS ARE OF TWO TYPES :
 Transmission Gratings
 Reflection Gratings
 UV gratings have 2000-6000 grooves per mm , IR gratings have 10-100 grooves per mm,
Materials used for construction are Quartz, NaCl, KBr.
MONOCHROMATORS

11.  SAMPLING OF SOLIDS
 Solids run in solution
 Mull technique
 Pressed pellet technique
 Solids films
 SOLID RUN IN SOLUTION
 Dissolve solid sample in non-aqueous solvent (which should be IR inactive) 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 sepectrometer. ◦ E.g. of solvents – acetone, cyclohexane,
chloroform, carbon tetrachloride etc.
 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.
SAMPLING

12.  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 an
evacuable die to form a small pellet( 1-2mm thick and 1cm in diameter).
Advantages:-
 Eliminates bands which appear due to mulling agent.
 Pellets can be stored for longer period of time.
 Concentration of sample can be adjusted.
Disadvantages:-
 Not suitable for polymers which are difficult to bind with KBr.
 High pressure may change the crystallinity of the sample.
 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.

14.  SAMPLING OF LIQUID
It consists of a sampling liquid as a thin films squeezed between
two infrared transparent windows like NaCl flats.
The salt plates or rock salt flats must be optically polished &
cleaned immediately after use. Toluene, chloroform etc are used to
clean them. They should be dry & handled only by their edges.
 The thickness of the film can be adjusted by varying pressure used
to squeeze the flats together(0.01-0.1 mm). It consists of two
windows of pressed salt sealed and separated by thin gaskets of
Teflon, copper or lead that have been wetted with mercury. The
windows are usually made of sodium chloride, potassium chloride
or cesium bromide.
There are two cells, first cell containing sample & second one
containing pure solvent placed in reference beam. By the reference
beam solvent absorptions are cancelled out & spectrum recorded is
that of solute alone.

15.  SAMPLING OF GASES
Infrared transparent windows allow the cell to be mounted directly.
Internal mirrors are used which permit the beam to be reflected
several times through the sample to increase the sensitivity.
In vapor phase, rotational changes in molecule occur freely & these
low frequency processes can modulate the higher energy
vibrational bands

16. THERMOCOUPLE
BOLOMETER
PYROELECTRIC DETECTORS
PHOTOCONDUCTING DETECTORS
GOLAY CELLS
DETECTORS

17. MOLECULAR VIBRATIONS

18. MOL. VIBRATION ARE DIVIDED INTO 2 MAIN TYPES:
 FUNDAMENTAL VIBRATIONS: Vibrations which appear as band in
the spectra.
 NON- FUNDAMENTAL VIBRATIONS: Vibrations which appears as a
result of fundamental vibrations.
FUNDAMENTAL VIBRATION IS ALSO DIVIDED INTO TYPES:
 STRECHING VIBRATION: Involves a continuous change in the inter
atomic distance along the axis of the bond b/w 2 atoms. It requires more
energy so appear at shorter wavelength.
 BENDING VIBRATIONS: are characterized by a change in the angle
b/w two bonds. It requires less energy so appear at longer wavelength.

19.  STETCHING VIBRATIONS
 SYMMETRIC VIB: Inter atomic distance b/w 2 atoms increases/decreases.
 ASYMMETRIC VIB: Inter atomic distance b/w 2 atoms is alternate/opposite.
 BENDING VIBRATIONS
 IN PLANE BENDING: If all the atoms are on same plane.
 OUT OF PLANE BENDING: If 2 atoms are on same plane while the 1 atom is
on opposite plane.
 IN PLANE BENDING IS DIVIDED INTO
 SCISSORING: When 2 atoms move away or close towards each other.
 ROCKING: Change in angle b/w a group of atoms.
 OUT OF PLANE BENDING IS DIVIDED INTO
 WAGGING: Change in angle b/w the plane of a group of atom.
 TWISTING: Change in angle b/w the plane of 2 groups of atoms.

20. IR spectra is divided into 2 regions:
 REGION 4000- 1500 CM-1 :
It consists of absorption bands of vibrational states of various types
of bonds present in the molecule. The important groups accounted for
include NH, OH, C=O, C=C, C=N, etc. The presence of aromatic
nucleus (2000-1670 cm-1) and hydrogen bonding O-H, N-H, etc are
also encountered in this region.
For example, a sharp band around 2200-2400 cm-1 would indicate
the possible presence of a C-N or a C-C triple bond.
REGIONS OF IR SPECTRUM

21.  FINGERPRINT REGION :
Fingerprint region is further divided into three regions.
 Region 1500- 1350 cm-1 :
The presence of double peaks near 1380 cm-1 and 1365 cm-1 indicates
presence of tertiary butyl group in the compound.
 Regions 1350-1000 cm-1 :
Characteristic strong bands due to C-O stretching are present. Absorption in
the IR region 1150-1070 cm-1 is most characteristic of ethers, Primary
alcohols forms two strong bands b/w 1350-1260 cm-1 and Near 1050 cm-1,
Esters shows two strong bands b/w 1380-1050 cm-1, Phenols absorbs Near
1200 cm-1.
 Less than 1000 cm-1:
Absorption band in the region 750-700 cm-1 indicates the presence of
mono substituted benzenes. Geometrical isomers of olefins can be
distinguished in the region 970 – 700 cm-1. Cis- isomer shows strong
intensity absorption band at 700 cm-1 and trans- isomer at 970-960 cm-1.

22.  Identification of functional groups & structure elucidation of
organic compounds.
 Quantitative analysis of a number of organic compounds.
 Study of covalent bonds in molecules.
 Studying the progress of reactions.
 Detection of impurities in a compound.
 Ratio of cis-trans isomers in a mixture of compounds.
 Protein quantitation
APPLICATIONS OF IR
SPECTROSCOPY

23.  Cannot determine the molecular weight of the compound.
 Does not give information about the relative position of different
functional groups in a molecule.
 From the single IR spectrum of an unknown substance, it is not
possible to know whether it is pure compound or a mixture of
compound.
 Sample cells are made of halogen salts which are susceptible to
moisture.
LIMITATIONS OF IR
SPECTROSCOPY

24.  Plastics play an enormous role in modern manufacturing—from
functioning as a primary packaging material to serving as the end-
product itself. And its prevalence in our daily lives and businesses
is especially visible in the volume of plastic parts, from plumbing
fixtures to screwdriver handles, produced every year.
 Of course, as a key piece of the business, manufacturers need to
not only ensure quality and function of plastic products and parts,
but also have the ability to troubleshoot if a product fails, fractures,
or malfunctions. And when the need arises, plastics failure analysis
can be an effective and fast method for determining what caused a
failure.
CASE STUDY - PLASTICS
FAILURE ANALYSIS USING FTIR

25.  Fourier transform infrared spectroscopy (FTIR) is one technique that can
be used for such an analysis, helping identify organic and some inorganic
materials through the application of infrared radiation. Here’s one
example of how we used FTIR to conduct plastics failure testing and
analysis to uncover why a “bad” part failed.
PROBLEM
 After a plastic part fractured during use, the manufacturer needed to
determine the cause so it could make adjustments to the manufacturing
process and mitigate the issue going forward. With a working part in-
hand, the manufacturer engaged our expert team to help, submitting a
“good” and “bad” part to be sampled, analyzed, and compared.
SOLUTION
 With both a good and bad part submitted for analysis, our team’s goal
was to uncover any differences in the chemical composition of the two
materials. This led to a two-step FTIR plastics analysis:
 Step 1: A material sample from each part was collected, analyzed via
FTIR, and compared. The results showed that the bulk of the materials
comprising each part were very similar. And in order to zero-in on any
differences, an additional tactic was needed.

26. Step 2: Our analysts made the decision to soak the parts in isopropyl
alcohol in order to extract compounds present in the parts. The alcohol was
decanted and then evaporated. The remaining residues from the extracts
were then analyzed using attenuated total reflectance FTIR (ATR-FTIR).
RESULTS
 After our two-step analysis, the FTIR spectra obtained revealed that each
of the extracts contained dioctylphthalate (DOP), which is a common
plasticizer.
 However, a significantly smaller amount was extracted from the
fractured part, as compared to the good part. In the figure below, you can
see the difference.
 As a result, our analysts concluded that the plastic part failed due to an
insufficient amount of plasticizer present. And with these results in-hand,
the manufacturer could move forward with production adjustments to
prevent future fractures and failures.

28.  Gurdeep R Chatwal, Sham K Anand, Instrumental method of
chemical analysis, Himalaya publishing house, pg 2.29-2.82
 Satinder Ahuja and Neil Jespersen “Modern Instrumental Analysis
(Comprehensive Analytical Chemistry)” Volume 47. Chapters 1
and 5. First Edition. The Netherlands 2006.
 G. H. Jeffrey, J. Bassett, J. Mendham and R. C. Denney. “Vogel’s
Textbook of Quantitative Chemical Analysis” Chapter 19. Fifth
Edition. UK 1999.
 Donald L. Pavia, Gary M. Lampman and George S. Kriz.
“Introduction to Spectroscopy. A Guide for Students of Organic
Chemistry” Chapter 2. Thompson Learning. United States of
America 2001.
REFERENCES

29. THANK YOU