FTIR-Presentazione (1)

8/2/2019 FTIR-Presentazione (1)

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Fourier Transform Infrared(FT-IR) Spectroscopy

Theory and Applications

THE ELECTROMAGNETIC SPECTRUM

INFRAREDGAMMA RAYS X RAYS UV VISIBLE


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Introduction to FTInfrared

Spectroscopy

What is infrared spectroscopy?

Theory of FT-IR

FT-IR Advantages?

New FT/IR4000-6000Series


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What is Infrared? Infrared radiation lies between the visible and microwave portions

of the electromagnetic spectrum.

Infrared waves have wavelengths longer than visible and shorterthan microwaves, and have frequencies which are lower thanvisible and higher than microwaves.

The Infrared region is divided into: near, mid and far-infrared.

Near-infrared refers to the part of the infrared spectrum that isclosest to visible light and far-infrared refers to the part that iscloser to the microwave region.

Mid-infrared is the region between these two.

The primary source of infrared radiation is thermal radiation. (heat)

It is the radiation produced by the motion of atoms and moleculesin an object. The higher the temperature, the more the atoms andmolecules move and the more infrared radiation they produce.

Any object radiates in the infrared. Even an ice cube, emitsinfrared.


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What is Infrared? (Cont.)

Humans, at normal body temperature, radiatemost strongly in the infrared, at a

wavelength of about 10 microns (A micronis the term commonly used in astronomy fora micrometer or one millionth of a meter). In

the image to the left, the red areas are thewarmest, followed by yellow, green and

blue (coolest).

The image to the right shows a cat in theinfrared. The yellow-white areas are thewarmest and the purple areas are the coldest.

This image gives us a different view of afamiliar animal as well as information that wecould not get from a visible light picture.Notice the cold nose and the heat from the cat'seyes, mouth and ears.


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Infrared Spectroscopy

The bonds between atoms in the molecule stretch and bend,

absorbing infrared energy and creating the infrared

spectrum.

Symmetric Stretch Antisymmetric Stretch Bend

A molecule such as H2O will absorb infrared light when the vibration

(stretch or bend) results in a molecular dipole moment change


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Energy levels in Infrared Absorption

Infrared absorption occurs among the ground vibrational states, the

energy differences, and corresponding spectrum, determined by the

specific molecular vibration(s). The infrared absorption is a net

energy gain for the molecule and recorded as an energy loss for the

analysis beam.

hExcited

states

Ground

(vibrational)

states

h(1 -0 )h(1 - 0)

h(2 - 1)(overtone)

Infrared Absorption and

Emission

1

2

0

3


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A molecule can be characterized (identified) by its molecularvibrations, based on the absorption and intensity of specific

infrared wavelengths.


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For isopropyl alcohol, CH(CH3)2OH, the infrared absorptionbands identify the various functional groups of the molecule.


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Capabilities of Infrared Analysis

Identification and quantitation of organic solid,liquid or gas samples.

Analysis of powders, solids, gels, emulsions,

pastes, pure liquids and solutions, polymers, pure

and mixed gases.

Infrared used for research, methods development,

quality control and quality assurance applications.

Samples range in size from single fibers only 20

microns in length to atmospheric pollution studies

involving large areas.


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Applications of Infrared Analysis

Pharmaceutical research Forensic investigations

Polymer analysis

Lubricant formulation and fuel additives

Foods research

Quality assurance and control

Environmental and water quality analysis

methods

Biochemical and biomedical research

Coatings and surfactants

Etc.


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To separate IR light, a grating is used.

Grating

Light source

Detector

Sample

Slit

To select the specified IR light,

A slit is used.

Dispersion

SpectrometerIn order to measure an IR spectrum,

the dispersion Spectrometer takes

several minutes.

Also the detector receives only

a few % of the energy of

original light source.

Fixed CCM

B.S.

Moving CCM

IR Light source

Sample

Detector

An interferogram is first made by

the interferometer using IR light.

The interferogram is calculated and transformed

into a spectrum using a Fourier Transform (FT).

FTIRIn order to measure an IR spectrum,

FTIR takes only a few seconds.

Moreover, the detector receives

up to 50% of the energy of originallight source.

(much larger than the dispersion

spectrometer.)

Comparison Beetween Dispersion Spectrometer and

FTIR


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Interferogram

is made by an interferometer.

Interferogram

is transformed

into a spectrum using a FT.

BKG

SB

3000 2000 1000

[cm-1]

Sample

SB

Sample

3000 2000 1000

[cm-1]

Sample/BKG

IR spectrum

%T

3000 2000 1000 [cm-1]

The Principles of FTIR Method


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FTIR seminar

Intensity Distribution and Temperature Dependency versus Wavelength of

Black Body Radiation Energy

2 5 2010

105

104

103

102

10

1

10-1

10-2

10-3

10-4

0.1 0.2 0.5 1 50 100

Wavelength / m

6000K

4000K

2000K

1000K

500K

300K

200K

Spe

ctralirradianceW

IR light source

IR Light Source


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FTIR seminar

Interferometer

He-Ne gas laser

Fixed mirror

Movable mirror

Sample chamber

Light

source

(ceramic)

Detector

(DLATGS)

Beam splitter

FT Optical System Diagram


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Fixed mirror

Movable mirror

Fixed mirror

Movable mirror

Fixed mirror

Movable mirror

Same-phase interference

wave shape

Opposite-phase

interference

wave shape

Same-phase interference

wave shape0

Movable mirror

Interference pattern of lightmanifested by the optical-path

difference

Continuous phase shift

Signalstrength

(X)

-2 - 0 2

-2 - 0 2

FTIR seminar

Interference of two beams of light


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Relationship between light source spectrum and the signal output from interferometer

(a) Monochromatic

light

(b) Dichroic light

(c) Continuous

spectrum light

All intensities are standardized.

Light source spectrum Signal output from interference wave

Time t

Time t

Time tI(t)

I

( )

Wavenumber

Wavenumber

Wavenumber

IAz

Az

FTIR seminar

Interference is a superpositioning of waves


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FTIR seminar

Interferometer interferogram

Output of a Laser interferometer

Primary interferometer interferogram

that was sampled

Optical path difference x

Sampling of an actual interferogram


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4000 400

SBFourier transform

Optical path difference[x]

(Interferogram) (Single beam spectrum)

Wavenumber[cm-1]

Single

st

rength

Time axis by FFT Wavenumber

Fourier Transform


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FTIR seminar

TGS

Operates at room temperature

MCT

Operates at the temperatur

of liquid nitrogen

D*(,

f)(cmHz

1/2W-1)

1010

109

108

Wavenumber[cm-1]4000 600

Detector Properties


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1.Better sensitivity and brightness

- Allows simultaneous measurement over the entire wavenumber range- Requires no slit device, making good use of the available beam

2.High wavenumber accuracy

- Technique allows high speed sampling with the aid of laser light interference fringes

- Requires no wavenumber correction

- Provides wavenumber to an accuracy of 0.01 cm-1

3. Resolution

- Provides spectra of high resolution

4. Stray light

- Fourier Transform allows only interference signals to contribute to spectrum.

Background light effects greatly lowers.

- Allows selective handling of signals limiting intreference

5. Wavenumber range flexibility

- Simple to alter the instrument wavenumber range

CO2 and H2O sensitive

FT-IR Advantages and Disadvantages


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FT-IR Advantages

Fellgett's (multiplex) Advantage

FT-IR collects all resolution elements with a completescan of the interferometer. Successive scans of the FT-IR instrument are coadded and averaged to enhance thesignal-to-noise of the spectrum.

Theoretically, an infinitely long scan would average outall the noise in the baseline.

The dispersive instrument collects data one wavelengthat a time and collects only a single spectrum. There isno good method for increasing the signal-to-noise of thedispersive spectrum.


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FT-IR Advantages

Connes Advantage

an FT-IR uses a HeNe laser as an internal wavelength

standard. The infrared wavelengths are calculated

using the laser wavelength, itself a very precise and

repeatable 'standard'.Wavelength assignment for the FT-IR spectrum is very

repeatable and reproducible and data can be compared

to digital libraries for identification purposes.


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FT-IR Advantages

Jacquinot Advantage

FT-IR uses a combination of circular apertures andinterferometer travel to define resolution. To improvesignal-to-noise, one simply collects more scans.

More energy is available for the normal infrared scanand various accessories can be used to solve varioussample handling problems.

The dispersive instrument uses a rectangular slit tocontrol resolution and cannot increase the signal-to-noise for high resolution scans. Accessory use islimited for a dispersive instrument.


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FT-IR Application Advantages

Opaque or cloudy samples

Energy limiting accessories such as diffuse reflectance or FT-

IR microscopes

High resolution experiments (as high as 0.001 cm-1 resolution)

Trace analysis of raw materials or finished products

Depth profiling and microscopic mapping of samples

Kinetics reactions on the microsecond time-scale

Analysis of chromatographic and thermogravimetric sample

fractions


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FT-IR Terms and Definitions

Resolution (common definition) The separation of the variousspectral wavelengths, usually

defined in wavenumbers (cm-1).

A setting of 4 to 8 cm-1 is sufficient

for most solid and liquid samples.Gas analysis experiments may need

a resolution of 2 cm-1 or higher.

Higher resolution experiments will

have lower signal-to-noise.


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Resolution FT/IR Case

A spectrum is said to be collected ata resolution of 1 cm-1 if 4 datapoints are collected within eachspectral interval of 1 cm-1 .

In order to acquire a spectrum athigher, an increased number of data

points is needed, requiring a longerstroke of the moving mirror.

For higher resolution instrumentsan aperture is needed in order toimprove parallelism withininterferometer.


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Apodization - amathematical operation toreduce unwantedoscillation and noisecontributions from the

interferogram and to avoidaberrations coming fromthe finite nature of real(non theoreticalinterferograms). Commonapodization functionsinclude Beer-Norton,Cosine and Happ-Genzel.

Apodization


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Scan mode - Either single

beam or ratio. Single

beam can be a scan of the

background (no sample)

or the sample. Ratio

mode always implies the

sample spectrum divided

by, or ratioed against, the

single beam background.


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Scan(s) - a complete cycle of movement of the

interferometer mirror. The number of scans collected

affects the signal-to-noise ratio (SNR) of the final

spectrum. The SNR doubles as the square of the

number of scans collected; i.e. 1, 4, 16, 64, 256, .

Scan speed or optical path velocity - the rate at which

the interferometer mirror moves. For a DTGS detector,

the SNR decreases as the scan speed increases.

Scan range - spectral range selected for the analysis.

The most useful spectral range for mid-infrared is 4000to 400 cm-1.


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The highest S/N ratio in the world, 50,000:1 (FT/IR-6300) (Over sampling with 24-bit ADC)

DSP-driven interferometer andnew ADC (18-bit to 24-bit)

Digital control of the moving mirror drive using an advanced high speed digital signal processor (DSP) technologyThe outstanding performance of the ADC (Analog-to digital converter) and DSP (Digital signal processor) allows very rapid and accurate correction

for the effects of velocity and position errors.

Autoalignment for all models (The interferometer optics can always be aligned by the PC)

In addition to proven technology for Rapid scanning and vacuum capabilities;

a Step scan capability enables time-resolved studies similar to research models by Nicolet, Bruker and Bio-Rad.

IR imaging with IMV-4000 multi-channel microscope for all models (Rapid scanning with a linear array MCT detector )

PC communication and control using USB

Aperture of7.1, 5.0, 3.5, 2.5, 1.8, 1.2, 0.9, 0.5 mm diameter for FT/IR-4100/4200

Spectra Manager II (cross-platform software suite for JASCO spectroscopy systems) (Spectra Manager CFR: 21 CFR Part

11 compliance)

Research model capability (Upgradeable wavelength extension, high resolution, step scan)

Improved Water Vapor and CO2 Compensation

New Features of FTIR4000-6000Series


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Polymer shell

Improved instrument design

Compact sizeSample compartment with

same size as a higher class

model

FT/IR-400 Plus

Aperture

No additional optics for IR microscope interface

Standard apertures for optimum S/N and resolution capability

Easy replacement of light source and detector

FT/IR-4100

FT/IR-4200Microscope

FTIR4000 Series


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FT/IR-4000 Series purge design

N2gas inlet

Control valve

Instrument purge is standard for all models of the FT/IR-4000 Series.

FTIR4000 Series Purge System


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Conventional method

Find the zero crossings, then interpolate

a matching set of IR data points.

Over sampling method

Reduction of high frequency noise by over sampling with a 16 times greater

number of sampling points enables improvement of the S/N ratio.

Pre-amp.

Analog circuit

Photo coupler

Voice Coil

HeNe laser

Photo coupler

Pre-amp.

ADC

DSPDAC

Clock

24-bit AD

Voice Coil

HeNe laser

Accurate mirror drive

And reduce flutter at

low wavenumber range.

FT/IR-4000 & 6000 series

S/N ratio (Oversampling system)


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FT/IR-6000 Series purge design

N2gas inlet

Purge control valve front side

Instrument purge is standard for all models of the FT/IR-6000

Series.

FTIR6000 Series Purge/Vacuum System

FTIR-Presentazione (1)

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