INFRARED SPECTROSCOPY

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INFRARED SPECTROSCOPY

• Pn. Suryati Bt. Syafri
• En. Maywan Hariono
• 2009

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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

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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.

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Light Electromagnetic Spectrum
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IR Application

• Broadly applied in several area sort of
• Army
• Fire man
• Veterinary
• Pharmacy
• Electronic devices
• Remote sensing

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IR spectrum

• Divided into 3 regions
• Near Infrared
• Middle Infrared
• 3. Far Infrared

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Spektrum IM
Ranges Far Infrared Middle Infrared Near Infrared
Wavelength range 50-1000µm 2.5-50µm 0.8-2.5µm
Wavelength number 200-10cm-1 4000-200cm-1 12500-4000 cm-1
Energy range 0.025-0.0012eV 0.5-0.025eV 1.55-0.5eV
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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

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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 CC (2100-2200), CN
  (2240- 2280)
• Double bonds CO (1680-1750), CC
  (1620-1680)
• Single bond C-O (1025-1200)

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Intensity Trends

• Follows change in dipole caused by vibrating
  atoms
• Polar bonds (strong bond dipoles) absorb strongly
• O-H
• CO, CN
• C-O
• Nonpolar bonds absorb weakly
• CC, CC
• Follows overlapping bands
• CH bands tend to overlap
• Molecules contain many CH
• CH absorptions tend to be strong

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PRINCIPLES

• For each molecules, there is a various kind of
  vibration occurs

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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 dont have a
  dipole moment, means no IR absorption occurs
• SO2 dan CO2 have a dipole moment so it will give
  IR absorption

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• 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

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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 CC , CN
3. 2000-1500 cm-1, double bond, ex CO, CC, CN
4. 1500-400 cm-1, an absorption that involves the
   deformation of other bondings

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Fingerprint region (lt1500 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

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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

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Instrumentation

• Conventional method(dispersive instrument)
• The monochromator being used to select frequency
  of one radiation in one time through the sample.

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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

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Animation of FTIR
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IR Components

• A. IR Resources
• Quartz halogen
• Nernst Glower lamp (run at 2000oC)
• Globar (made from Carbide silicon, run at 1100oC)

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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

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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

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Sample preparation
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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

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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

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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)

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Instrumentation

• Display
• Exhibit the collected data
• Translate the data to the graph
• The graph is plotted as transmision vs frequnecy
  (wavenumbers)

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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

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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.

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aniline
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phenol
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Salycilic acid
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ethanol
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Contoh spektrum

• allopurinol

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• phenytoin

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References

• David G. watson (2005). Pharmaceuthical Analysis.
  Second edition. Pp115-128
• http//en. Wikipedia.org./wiki/Infrared
  spectroscopy
• http//www.chem.ualberta.ca/orglabs/procedures/In
  frared Spectroscopy/ir/IR20Main.html