INFRARED SPECTROSCOPY
Pn. Suryati Bt. Syafri
En. Maywan Hariono
2009
What is IR light?
Is a kind of electromagnetic radiation
which has wave region longer than
visible light, but shorter than radio
wave.
Low energy
What is IR region?
The wavelength region is 2.5-25 µm
The unit commonly used is
wavenumbers (cm-1 ) i.e. 4000-400
cm-1
Remember that Wavenumber is
proportional with energy (E) and
frequency (v), but reciprocal with
wavelength.
Light & Electromagnetic Spectrum
IR Application
-
Broadly applied in several area sort
of :
Army
Fire man
Veterinary
Pharmacy
Electronic devices
Remote sensing
IR spectrum
Divided into 3 regions
1. Near Infrared
2. Middle Infrared
3. Far Infrared
Spektrum IM
Ranges
Far
Infrared
Middle
Infrared
Near
Infrared
Wavelength 50-1000µm 2.5-50µm
range
0.8-2.5µm
Wavelength 200-10cm-1 4000number
200cm-1
125004000 cm-1
Energy
range
1.55-0.5eV
0.0250.0012eV
0.50.025eV
Principles
When the certain molecules are exposed
to IR light, it will absorb the energy to
make the atoms of molecules vibrating
The vibration frequency depend on the
amount of atoms and the length and the
strength of atomic bonding
Molecule vibration is stimulated by
absorption radiation in the same
frequency with the frequency of its origin
vibrations
Energy Trends
Energy follows vibration frequency of
atoms
-light atoms vibrate more rapidly: -CH,
NH, OH vibrations . 2800 cm-1
Multiple bonds vibrate more rapidly:
triple bonds : C≡C (2100-2200), C≡N
(2240- 2280)
Double bonds : C=O (1680-1750), C=C
(1620-1680)
Single bond : C-O (1025-1200)
Intensity Trends
Follows change in dipole caused by
vibrating atoms
– Polar bonds (strong bond dipoles) absorb
strongly
O-H
C=O, C=N
C-O
– Nonpolar bonds absorb weakly
C=C, C≡C
Follows overlapping bands
– CH bands tend to overlap
– Molecules contain many CH
– CH absorptions tend to be strong
PRINCIPLES
For each molecules, there is a
various kind of vibration occurs
What kind of sample be able to
absorb IR radiation?
Only vibration which alters molecule dipole
moment (electron Hanya getaran yang
meyebabkan perubahan dipole molekul (the
magnitude of positive and negative charge
between two bonded atoms) and having the IR
absorption frequency in the IR region
Gas molecules such as O2, H2 and Cl2 don’t have
a dipole moment, means no IR absorption occurs
SO2 dan CO2 have a dipole moment so it will give
IR absorption
Every functional group has their own IR
absorption
The more complex in molecule structure,
the more complex in IR absorption
It is used to identify any functional group
presents in a molecule structure
IR Spectrum Distribution
1. 4000-2500 cm-1, absorption of atom
which is bond to H atom, ex: C-H, O-H
dan N-H
2. 2500-2000 cm-1, triple bond, ex: C≡C ,
C≡N
3. 2000-1500 cm-1, double bond, ex: C=O,
C=C, C=N
4. 1500-400 cm-1, an absorption that
involves the deformation of other
bondings
Fingerprint region (<1500 cm-1)
Many bands & many overlaps
– Heavy atom stretches
– All bends, etc.
– Should have simple molecule (or other
evidence or structure) before
intepreting bands in this region
Overall pattern reflects molecular
structure
– Pattern from 1400-600 = molecular
fingerprints
Prosedure
IR light is passed through the sample, and the amount of energy which is
absorbed by the sample per cm wavelength will be recorded .
The IR light desired will be selected by monochromator before exposed to
the sample’ Interferometer is used for measuring all wavelength in one
running time.
The data will be translated into the graph which is plotted as wavelength
vs transmision
The graph might be compared to known standard reference
Instrumentation
Conventional method(dispersive
instrument)
– The monochromator being used to
select frequency of one radiation in one
time through the sample.
Peralatan
Spektrometer FTIR (Fourir Transform IR)
– Semua frekuensi yang diperlukan melalui instrument sekaligus
– Menggunakan interferometer contohnya Michelson Interferometer
– Teknik cepat dan pantas
– Digunakan dikebanyakan makmal kimia
Animation of FTIR
IR Components
A. IR Resources
– Quartz halogen
Nernst Glower lamp (run at 2000oC)
– Globar (made from Carbide silicon, run
at 1100oC)
IR Components
B. sample
1. solids
– A. Nujol mull
The sample is ground using a mortar and pestle to
give a very fine powder
A small amount is then mixed with nujol (liquid
paraffin) togive a paste
Several drops of this paste are then applied between
two sodium chloride plates (these do not absorb
infrared in the region of interest)
The plates are then place in the instrument sample
holder ready for scanning
IR Components
B. Potassium Bromide disk
– A verry small amount of the solid
(approximately 1-2 mg) is added to pure
potassium bromide powder (approximately 200
mg) and ground up as fine as possible
– This is then placed in a small die and put
under pressure mechanically. The pressure is
maintained for several minutes before
removing the die and the KBr disk formed
– The disk is then placed in a sample holder
ready scanning
Sample preparation
Sample preparation
2. thin films
– The infrared spectrum of thin film can be easily obtained
by placing a sample in a suitable holder, such as a card
with a slot cut for the sample window
– This method is often used for checking the calibration of
an instrument with a polystrirene sample as the band
produced by this material are accurately known
3. liquids
– This is possibly the simplest and the common method
for sample preparation
– A drop of the sample is placed between two potassium
bromide or sodium chloride circular plates to produce a
thin capillary film
– The plates are then placed in a holder ready for analysis
Sample preparation
4. gases
– To obtaine an infrared spectrum of a
gas requires the use of a cylindrical gas
cell with windows at each end composed
of an infrared inactive material such as
KBr, NaCl or CaF2
– The cell usually has an inlet and outlet
port with atap to enable the cell to be
easilly filled with the gas to be analyzed
instrumentation
C. monochromator/interferometer
– Break down the radiation of light to the
different wave region in one time
running process.
D. detector
– CCD (charge couple device)
– InGaAs (Indium Gallium Arsen)
– Pbs (Lead sulfide)
Instrumentation
Display
– Exhibit the collected data
– Translate the data to the graph
– The graph is plotted as transmision vs
frequnecy (wavenumbers)
Advantages
Provide the fingerprint for the
sample being analyzed
The installation of instrument to the
computer allows the comparison of
sample spectrum and standard
reference can be run simultaneously
Disadvantages
Rarely used for quantitative purpose
since the spectrum produced is too
complicated to determine one by one
The sample preaparation is quite
difficult, needs the skill to handle it.
aniline
phenol
Salycilic acid
ethanol
Contoh spektrum
allopurinol
phenytoin
References
David G. watson (2005).
Pharmaceuthical Analysis. Second
edition. Pp:115-128
http://en.
Wikipedia.org./wiki/Infrared
spectroscopy
http://www.chem.ualberta.ca/~orgla
bs/procedures/Infrared
Spectroscopy/ir/IR%20Main.html