FOURIER TRANSFORM INFRARED

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FOURIER TRANSFORM INFRARED UV-VIS
SPECTROSCOPYBY ASHLEY W, HARMITA, PETER, LE
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F T I R

• Fourier Transform Infrared spectroscopy
• WHAT IS IT ?
• It is an instrument that is commonly used to
  identify functional groups of organic compounds
  by measuring the vibration frequencies of
  molecules when they are scanned with an infrared
  light

www.chemistry.nmsu.edu
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Vibrations

• Atoms in the molecule are subjected to number of
  vibrations.

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Theoretical principles

• In infrared spectroscopy wavelength is measured
  in wave numbers which have the units cm-1
• IR radiation does not have enough energy to
  induce electronic transitions as seen with UV.
  Absorption of IR is restricted to compounds with
  small energy differences in the possible
  vibrational and rotational states.
• For a molecule to absorb IR, the radiation must
  interact with the electric field caused by
  changing dipole moment

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Calibration
www.internationalcrystal.net
www.chemistry.oregonstate.edu/courses/ch361-464/ch
362/irinstrs.htm - 9

• This device is precisely calibrated by using
  polystyrene calibration film.
• Size of peaks ? amount of material

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Background Spectrum

• This background spectrum can be used to compare
  with the sample measurement to determine
  transmittance
• Peaks in this region are characteristic of
  specific kinds of bonds, thus can be used to
  identify whether a specific functional group is
  present.

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Example of C-H(functional group) spectra

• Peaks in the region of (3000- 3100) cm-1
  indicates that sp2 hybridized C-H bond are
  present in the sample
• And peaks in range of (2800-3000)cm-1 indicates
  that sp3 hybridized C-H bond are present in a
  sample

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  Acids 1650-1700cm-1 Esters 1740-1750cm-1
Aldehydes 1720-1750cm-1 Ketones
1720-1750 cm-1 Amides1650-1715 cm-1
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FTIR Spectrum of Sample (98 N,N-Dimethylamphetami
ne Hydrochloride)
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What information can FT-IR provide

• It can determine the amount of components in a
  mixture
• It can determine the quality or how consistent a
  sample is
• It can identify unknown materials

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How FTIR works?

• Source Infrared energy is emitted from a glowing
  black-body source. Ends at the Detector
• Interferometer beam enters the interferometer
  where the spectral encoding takes place
• Interferogram signal then exits the
  interferometer
• Beamsplitter takes the incoming beam and divides
  it into two optical beams
• Sample beam enters the sample compartment where
  it is transmitted through or reflected off of the
  surface of the sample
• Detector The beam finally passes to the detector
  for final measurement
• Computer measured signal is digitized and sent
  to the computer where the Fourier transformation
  takes place
• Moving mirror in the interferometer is the only
  moving part of the instrument
• Fixed mirror

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Is FT-IR Qualitative, Quantitative, or
Comparative?

• Qualitative
• -Because each different material is a unique
  combination of atoms, no two compounds produce
  the exact same infrared spectrum
• -the size of the peaks in the spectrum is a
  direct indication of the amount of material
  present

• Quantitative and Comparative
• -Since it is sensitive, accurate, and has
  software algorithms, the quantitative methods can
  be developed and calibrated easily to perform
  various analysis
• -FT-IR is comparative due to the background
  spectrum that is compared to the sample

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Advantages/disadvantages

• Speed
• Sensitivity
• Mechanical simplicity
• Internally calibrated

• Destructive
• Too sensitive that it would detect the smallest
  contaminant

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Forensic Lab use

• A Forensic Scientist would use FT-IR to identify
  chemicals in different types of samples
• Paints
• Polymers
• Coatings
• Rugs
• Contaminants
• Explosive residues

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UV-Vis Spectometer
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UV-Vis

• Ultraviolet and visible spectrometers have been
  in general use for the last 35 years
• UV-Vis Spectrometers are used in many
  applications for there simplicity, versatility,
  speed, accurateness and cost effectiveness
• There are often other methods available but
  because of these qualities it is used
• One of the most important and widely used
  scientific instruments in the world

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Uses of UV-Vis

• In 1941 Arnold Beckmans company National
  Technical Laboratories introduced the first
  spectrometer in a single case
• These examples illustrate the impact of that
  original instrument
• the presence of vitamin A in foods using this
  instrument. Vitamins have unique absorption
  patterns in ultraviolet light
• analyze the structure of penicillin so that the
  molecule could then be synthetically produced in
  large quantities during WWII
• used in the analysis of crude oil for two
  important substances benzene and toluene found
  in TNT (WWII)

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Qualitative

• Routinely used in the quantitative determination
  of solutions of transitional metal ions and
  highly conjugated organic compounds
• Beer-Lambert law states that the absorbance of a
  solution is directly proportional to the
  solution's concentration. Thus UV - VIS can be
  used to determine the concentration of a solution

A -log10(I/Io)
e.c.L A measured absorbance I
the transmitted intensity Io the
intensity of the incident light at a given
wavelength L the path length
through the sample ? molar
absorptivity constant C
concentration
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Basic Components of UV-Vis

• Light Source
• Monochromator (wavelength detector)
• Cuvettes (sample)
• Detector

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Basic Components of UV-Vis cont

• Light source (2 components)
• Source of UV radiation
• Deuterium excited under low pressure which
  produces a constant UV spectrum, emits
  wavelengths of 160 375nm
• Visible light source
• Tungsten filament lamp emits in the spectrum of
  350 2500nm
• monochromator (5 components)
• entrance slit
• collimating lens
• dispersing device
• focusing lens
• exit slit

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Calibrations

• To calibrate the UV-VIS spectrometer you place a
  common solvent in one of the cuvettes and the
  spectrometer will read the solvent and the sample
  at the same time
• Solvent for water soluble compounds is usually
  water whilst the solvent for organic compounds is
  usually ethanol

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References

• http//www.wooster.edu/chemistry/is/brubaker/ir/ir
  _works_modern.html
• http//www.forumsci.co.il/HPLC/FTIR_page.html
• http//www.infrared-analysis.com/info1.htm
• http//teaching.shu.ac.uk/hwb/chemistry/tutorials/
  molspec/uvvisab3.htm
• http//icn2.umeche.maine.edu/genchemlabs/Spectra/S
  pectra.htm
• http//www.wfu.edu/chem/courses/organic/UV/index.h
  tml
• http//www.ptli.com/testlopedia/tests/UV-VIS-SPEC.
  asp
• www.thermonicolet.com
• http//teaching.shu.ac.uk/hwb/chemistry/tutorials/