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