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Fourier Transform
Infrared Spectroscopy
ABOUTFTIR
BACKGROUND
MECHANISMPROCESS
USES
ADVANTAGES
DISADVANTAGES
OPERATIONPRINCIPLE
SAMPLE PREPARATION
DATAANALYSIS
TYPES
DEVICE
TRANSMISSIONTECHNIQUES
ABOUTFTIR
FT-IR stands for Fourier Transform
InfraRed.
Named after J.B.J. Fourier
Includes the absorption, reflection, emission, or photoacoustic
spectrum obtained by Fourier
transform of an optical
interferogram.
ABOUTFTIR
ABOUTFTIR
Identification of unknown materials
Determination of the quality or
consistency of a sample
Determination of the amount of
components in a mixture
DEVELOPMENTALBACKGROUND
• late 1880s – Albert A. Michelson invented the Michelson Interferometer.
•Performed the experiment to determine the
speed of light. (Michelson – Morley experiment).
•1907 – Michelson received the Nobel Prize in
Physics • Michelson could not take advantage of the
field of Fourier Transform Spectroscopy (FTS).
SCHEMATIC DIAGRAMMICHELSON
INTERFEROMETER
DEVELOPMENTALBACKGROUND
1940s – Practical Fourier Transform Spectroscopy Used to measure light from celestial bodies.
1949 – first Fourier transform spectrum Different types of interferometers had been developed
•Lamellar grating
•Fabry-Perot interferometers
DEVELOPMENTALBACKGROUND
1960 – growing interest in interferometric spectroscopy
•J. W. Cooley and John Turkey – fast Fourier Transform (FFT) algorithm
Allowed Fourier transforms to be computed easily on computers available.
DEVELOPMENTALBACKGROUND
1966 – the first near – infrared planetary spectra was recorded 1969 – high resolution and high quality spectra of the planets
– first commercial FT-IR spectrometer was sold by Digilab.
DEVELOPMENTALBACKGROUND
1970 – commercial fourier transform spectometers became widely accessible. The first FT-IR spectrometers were large and expensive. 1981 – Robert Z. Muggli adapted a microscope to a FT-IR spectrometer. 1983 – Digilab and Spectra-Tech developed the first commercial FT-IR microspectrophotometer.
DEVELOPMENTALBACKGROUND
First low-cost spectrophotometer capable of recording an infrared spectrum was the Perkin-Elmer Infracord in 1957.
Covered the wavelength range from 2.5 μm to 15 μm
Lower wavelength limit - highest vibration frequency due to a fundamental molecular vibration.
Upper wavelength limit - spectral region or rock-salt region.
Later instruments used potassium bromide prisms and caesium iodide.
DEVELOPMENTALBACKGROUND
Region beyond 50 μm is the far-
infrared region
• Merges into the microwave
region.
diffraction gratings replaced
prisms as dispersing elements.
More sensitive detectors detect low
energy radiation.
Electronic computer needed to
perform the required Fourier
transform.
USES&APPLICATIONS
Identify unknown materials
Determine the quality or consistency of a sample
Determine the amount of components in a mixture
Analysis of liquid chromatography fractions.
Acquire spectrum of light emitted by the sample.
Photocurrent spectra.
USES&APPLICATIONS
Functional Group Analysis
Surface Molecular Composition
Chromatographic Effluents
Mixture Compound Determination
Stereochemistry
Molecular Orientation
Fingerprinting
Identification of Reaction components
Identification of Polymer, Resins, and Plastics
Formulation of Insecticides and Polymers
USES&APPLICATIONS
ADVANTAGES
Non-destructive technique
Provides a precise measurement method which requires no external calibration
Increase speed, collecting multiple scans simultaneously
Little Sample Preparation
Identifies structural isomers
Increase sensitivity and wavelength accuracy
Has greater optical throughput and resolution
Mechanically simple
DISADVANTAGES
FTIR do not measure spectra, only interferograms which are difficult to interpret.
Cannot use advanced electronic filtering techniques (lower S-N Ratio than Dispersive)
Noise sensitive - affects the radiation from infrared source Uses a single beam – changes in infrared absorbing gas can affect results
TYPESofFTIR
FAR-INFRARED FTIR
• developed for far-infrared range for mechanical tolerance needed for good optical performance. •A typical instrument was the cube interferometer developed at the NPL and marketed by Grubb Parsons.
TYPESofFTIR
NEAR-INFRARED FTIR
• The near-infrared region spans the wavelength range between the rock-salt region and the start of the visible region at about 750 nm.
•Fundamental vibrations can be observed in this region.
•It is used mainly in industrial applications such as process control and chemical imaging.
OPERATIONPRINCIPLE
I is the constant level with no modulation present.
The second term - spectrum.
The lower integration limit can be set to -∞ since B(σ) = 0 for all negative σ.
I(x) is defined as the modulated part of the interferogram.
OPERATIONPRINCIPLE
I(σ) is the light source intensity distribution
B(σ) is the modified source function.
DEVICE
Three basic spectrometer components in an FT system:
•Radiation source
•Interferometer
•Detector
DEVICE
IMV-4000 The newest most rapid FTIR
Array micrscope.
DEVICE
PARTS OF MICHELSON Interferometer
DEVICE
Interferometer produces a unique signal which contains infrared frequencies “encoded” into it
Mirrors reflects the beam transmitted
Beam Splitter takes the incoming infrared beam and divides it into two optical beams
Detector where all radiation incident on the interferometer is registered.
DEVICE
Spectrometer Layout
DEVICE
Spectrometer Layout
SPECTROMETERDESIGN
SPECTROMETERDESIGN
SPECTROMETERDESIGN
MECHANISM
1. The Source: Infrared energy is emitted from a glowing black-body source. This beam passes
• through an aperture which controls the amount of energy presented to the sample
2. The Interferometer: The beam enters the interferometer where the “spectral encoding” takes place.
• The resulting interferogram signal then exits the interferometer.
MECHANISM
3. The Sample: The beam enters the sample compartment where it is transmitted through or reflected off of the surface of the sample, depending on the type of analysis being accomplished.
• This is where specific frequencies of energy are absorbed.
MECHANISM
4. The Detector: The beam finally passes to the detector for final measurement. The detectors used are specially designed to measure the special interferogram signal. 5. The Computer: The measured signal is digitized and sent to the computer where the Fourier transformation takes place.
•The final infrared spectrum is then presented to the user for interpretation and any further manipulation.
MECHANISM
MECHANISMPROCESS
A collimator is irradiated with monochromatic light yielding a parallel ray of light.
The ray is split into two components in the beam splitter.
Following reflection in the mirrors another passage through the beam splitter occurs
Rays are added on the detector.
TRANSMISSIONTECHNIQUES
Solid Samples: • KBr Disk Technique
• Quantitative analysis of organic or inorganic substances in powder form.
• Thin-Film Technique
• Polymeric qualitative and quantitative analysis for substances in film form.
• Solution Technique
• Primarily qualitative analysis of substances dissolved in solvent.
• Uses liquid cells
TRANSMISSIONTECHNIQUES
Liquid Samples:
• Liquid Film Technique • Qualitative analysis of viscous and
nonvolatile substances
• Solution Technique • Qualitative analysis of liquids that dissolve
in solvent and nonvolatile substances
RELATEDTECHNIQUES
Nuclear magnetic resonance
• Additional information on detailed molecular structure
Mass spectrometry
• Molecular mass information and additional structural information
Raman spectroscopy
• Complementary information on molecular vibration.
• Facilitates analysis of aqueous samples.
SAMPLEPREPARATION
Samples State
• Any solid, liquid or gas sample
Amount • Solids:50 to 200 mg is desirable, but 10 μg
ground with transparent matrix
• 1 to 10 μg minimum is required if solid is soluble in suitable solvent.
• Liquids: 0.5 μL is needed if neat, less if pure.
• Gases: 50 ppb is needed
Preparation • Little or no preparation is required; suitable solvent
SAMPLEPREPARATION
Analysis Time •Estimated time: 1 to 10 min depending on the type of instrument and the resolution required. •Samples are prepared 1 to 5 min.
DATAANALYSIS
Emission Spectrum
• from a light source
• obtained by passing the light through a monochromator,
• Intensity of remaining light is measured.
• Intensity that was directly measured.
DATAANALYSIS
Absorption spectrum
• Light source with continuous spectrum in a broad wavelength range.
• Gas sample placed between the beam splitter and the detector.
• Measurement • Background acquired without the
sample cell • Measurement done with the cell
place in sample compartment.
• Difference of the measurements - measure of the absorption.
DATAANALYSIS
The spectrum of light of blue flame of butane torch.
Horizontal axis is the wavelength of light
Vertical axis represents amount of light emitted
DATAANALYSIS
DATAANALYSIS
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