fourier transform infrared spectroscopy (1)

8/2/2019 Fourier Transform Infrared Spectroscopy (1)

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Fourier TransformInfrared Spectroscopy


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ABOUTFTIR

BACKGROUND

MECHANISMPROCESS

USESADVANTAGES

DISADVANTAGES

OPERATIONPRINCIPLE

SAMPLE PREPARATION

DATAANALYSIS

TYPES

DEVICE

TRANSMISSIONTECHNIQUES


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ABOUTFTIR

FT-IR stands forFourier TransformInfraRed.

Named afterJ.B.J. Fourier

Includes the absorption, reflection,emission, or photoacousticspectrum obtained by Fourier

transform of an opticalinterferogram.


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ABOUTFTIR


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ABOUTFTIR

Identification of unknown materials

Determination of the quality orconsistency of a sample

Determination of the amount ofcomponents in a mixture


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DEVELOPMENTALBACKGROUND

late 1880sAlbert A. Michelson invented the

Michelson Interferometer.

Performed the experiment to determine the

speed of light. (Michelson Morleyexperiment).

1907 Michelson received the Nobel Prize in

Physics

Michelson could not take advantage of the

field ofFourier Transform Spectroscopy (FTS).


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SCHEMATIC DIAGRAMMICHELSONINTERFEROMETER


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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 gratingFabry-Perot interferometers


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1960 growing interest in

interferometric spectroscopy

J. W. Cooley and John Turkey

fast Fourier Transform (FFT)

algorithmAllowed Fourier transforms to be

computed easily on computers

available.


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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 byDigilab.


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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-Techdeveloped the first commercial FT-IR

microspectrophotometer.


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First low-cost spectrophotometer capable

of recording an infrared spectrum was the

Perkin-Elmer Infracord in 1957.

Covered the wavelength range from

2.5 m to 15 m

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.


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Region beyond 50 m is the far-infrared region

Merges into the microwaveregion.

diffraction gratings replacedprisms as dispersing elements.

More sensitive detectors detect lowenergy radiation.

Electronic computer needed toperform the required Fouriertransform.


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USES&APPLICATIONS

Identify unknown materials

Determine the quality or consistency of a

sample

Determine the amount of components in amixture

Analysis of liquid chromatography fractions.

Acquire spectrum of light emitted by the

sample.

Photocurrent spectra.


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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


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USES&APPLICATIONS


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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


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DISADVANTAGES

FTIR do not measure spectra, only

interferograms which are difficult to

interpret.

Cannot use advanced electronic filteringtechniques (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


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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.


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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.


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OPERATIONPRINCIPLE

I is the constant level with no modulation present.

The second term - spectrum.

The lower integration limit can be set to - sinceB() = 0 for all negative .

I(x) is defined as the modulated part of the

interferogram.


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OPERATIONPRINCIPLE

I() is the light source intensity distribution

B() is the modified source function.


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DEVICE

Three basic spectrometer components in an

FT system:

Radiation source

Interferometer

Detector


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DEVICE

IMV-4000 The newest most rapid FTIRArray micrscope.


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DEVICE

PARTS OF MICHELSON Interferometer


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DEVICE

Interferometerproduces a unique signal which contains

infrared frequencies encoded into it

Mirrorsreflects the beam transmitted

Beam Splittertakes the incoming infrared beam and

divides it into two optical beamsDetector

where all radiation incident on the

interferometer is registered.


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DEVICE

Spectrometer Layout


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DEVICE

Spectrometer Layout


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SPECTROMETERDESIGN


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SPECTROMETERDESIGN


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SPECTROMETERDESIGN


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MECHANISM

1. The Source: Infrared energy is emitted

from a glowing black-body source. This

beam passes

through an aperture which controlsthe amount of energy presented to the

sample

2. The Interferometer: The beam enters the

interferometer where the spectralencoding takes place.

The resulting interferogram signal

then exits the interferometer.


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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 beingaccomplished.

This is where specific frequencies of

energy are absorbed.


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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 thenpresented to the user for

interpretation and any further

manipulation.


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MECHANISM


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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.


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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


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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


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RELATEDTECHNIQUES

Nuclear magnetic resonance

Additional information on detailed

molecular structure

Mass spectrometry

Molecular mass information andadditional structural information

Raman spectroscopy

Complementary information on molecular

vibration.

Facilitates analysis of aqueous samples.


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SAMPLEPREPARATION

SamplesState

Any solid, liquid or gas sample

Amount Solids:50 to 200 mg is desirable, but 10 g

ground with transparent matrix

1 to 10 g minimum is required if solid issoluble in suitable solvent.

Liquids: 0.5 L is needed if neat, less ifpure.

Gases: 50 ppb is needed

Preparation Little or no preparation is required;suitable solvent


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SAMPLEPREPARATION

Analysis TimeEstimated time: 1 to 10 min depending on the

type of instrument and the resolution required.

Samples are prepared 1 to 5 min.

DATAANALYSIS


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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


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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 cellplace in sample compartment.

Difference of the measurements -

measure of the absorption.

DATAANALYSIS


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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


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DATAANALYSIS

DATAANALYSIS


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DATAANALYSIS

fourier transform infrared spectroscopy (1)

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