3. Spectroscopy
Spectroscopy
What is Infrared?
Infrared radiation lies between the visible and microwave portions
of the electromagnetic spectrum.
Infrared waves have wavelengths longer than visible and shorter
than microwaves, and have frequencies which are lower than
visible 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 is
closest to visible light and far-infrared refers to the part that is
closer 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 molecules
in an object. The higher the temperature, the more the atoms and
molecules move and the more infrared radiation they produce.
Any object radiates in the infrared. Even an ice cube, emits
infrared.
4. Spectroscopy
Spectroscopy
What is Infrared? (Cont.)
Humans, at normal body temperature, radiate
most strongly in the infrared, at a wavelength
of about 10 microns (A micron is the term
commonly used in astronomy for a
micrometer or one millionth of a meter). In
the image to the left, the red areas are the
warmest, followed by yellow, green and blue
(coolest).
The image to the right shows a cat in the
infrared. The yellow-white areas are the
warmest and the purple areas are the coldest.
This image gives us a different view of a
familiar animal as well as information that we
could not get from a visible light picture. Notice
the cold nose and the heat from the cat's eyes,
mouth and ears.
5. Spectroscopy
Spectroscopy
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
6. Spectroscopy
Spectroscopy
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.
hn
Excited
states
Ground
(vibrational)
states
h(n1 -
n0 )
h(n1 - n0)
h(n2 - n1)
(overtone)
Infrared Absorption and
Emission
n
1
n
2
n
0
n
3
9. Spectroscopy
Spectroscopy
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.
10. Spectroscopy
Spectroscopy
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.
11. Spectroscopy
Spectroscopy
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
Spectrometer
In 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).
FTIR
In order to measure an IR spectrum,
FTIR takes only a few seconds.
Moreover, the detector receives
up to 50% of the energy of original
light source.
(much larger than the dispersion
spectrometer.)
Comparison Beetween Dispersion Spectrometer
and FTIR
12. Spectroscopy
Spectroscopy
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
13. Spectroscopy
Spectroscopy FTIR seminar
Intensity Distribution and Temperature Dependency versus Wavelength of
Black Body Radiation Energy
2 5 20
10
105
104
103
102
10
1
10-1
10-2
10-3
10-4
0.1 0.2 0.5 1 50 100
Wavelength l / mm
6000K
4000K
2000K
1000K
500K
300K
200K
IR light source
IR Light Source
15. Spectroscopy
Spectroscopy
Fixed mirror
Ｂ
Movable mirror
Fixed mirror
Ａ
Movable mirror
Fixed mirror
Ｃ
Movable mirror
Same-phase interference
wave shape
Opposite-phase
interference
wave shape
Same-phase interference
wave shape
l
0
Movable mirror
Ｄ Interference pattern of light
manifested by the optical-path
difference
Continuous phase shift
Signal
strength
Ｉ
(X)
-2l -l 0 l 2l
-2l -l 0 l 2l
FTIR seminar
Interference of two beams of light
16. Spectroscopy
Spectroscopy
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 t
I(t)
I
b (u)
Wavenumber u
Wavenumber u
Wavenumber u
S I
SAz
Az
FTIR seminar
Interference is a superpositioning of waves
17. Spectroscopy
Spectroscopy FTIR seminar
Interferometer interferogram
Output of a Laser interferometer
Primary interferometer interferogram
that was sampled
Optical path difference x
Sampling of an actual interferogram
19. Spectroscopy
Spectroscopy FTIR seminar
TGS
Operates at room temperature
MCT
Operates at the temperatur
of liquid nitrogen
D*
(l,
f)
(cmHz
1/2
W
-1
)
1010
109
108
Wavenumber[cm-1]
4000 600
Detector Properties
20. Spectroscopy
Spectroscopy
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
21. Spectroscopy
Spectroscopy
FT-IR Advantages
Fellgett's (multiplex) Advantage
FT-IR collects all resolution elements with a complete
scan of the interferometer. Successive scans of the FT-
IR instrument are coadded and averaged to enhance the
signal-to-noise of the spectrum.
Theoretically, an infinitely long scan would average out
all the noise in the baseline.
The dispersive instrument collects data one wavelength
at a time and collects only a single spectrum. There is
no good method for increasing the signal-to-noise of the
dispersive spectrum.
22. Spectroscopy
Spectroscopy
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.
23. Spectroscopy
Spectroscopy
FT-IR Advantages
Jacquinot Advantage
FT-IR uses a combination of circular apertures and
interferometer travel to define resolution. To improve
signal-to-noise, one simply collects more scans.
More energy is available for the normal infrared scan
and various accessories can be used to solve various
sample handling problems.
The dispersive instrument uses a rectangular slit to
control resolution and cannot increase the signal-to-
noise for high resolution scans. Accessory use is
limited for a dispersive instrument.
24. Spectroscopy
Spectroscopy
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
25. Spectroscopy
Spectroscopy
FT-IR Terms and Definitions
Resolution (common definition) –
The separation of the various
spectral 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.
26. Spectroscopy
Spectroscopy
FT-IR Terms and Definitions
Resolution – FT/IR Case
A spectrum is said to be collected at
a resolution of 1 cm-1 if 4 data
points are collected within each
spectral interval of 1 cm-1 .
In order to acquire a spectrum at
higher, an increased number of data
points is needed, requiring a longer
stroke of the moving mirror.
For higher resolution instruments an
aperture is needed in order to
improve parallelism within
interferometer.
27. Spectroscopy
Spectroscopy
FT-IR Terms and Definitions
Apodization - a
mathematical operation to
reduce unwanted oscillation
and noise contributions
from the interferogram and
to avoid aberrations coming
from the “finite” nature of
real (non theoretical
interferograms). Common
apodization functions
include Beer-Norton,
Cosine and Happ-Genzel.
Apodization
28. Spectroscopy
Spectroscopy
FT-IR Terms and Definitions
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.
29. Spectroscopy
Spectroscopy
FT-IR Terms and Definitions
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 4000
to 400 cm-1.
30. Spectroscopy
Spectroscopy
The highest S/N ratio in the world, 50,000:1 (FT/IR-6300) (Over sampling with 24-bit ADC)
DSP-driven interferometer and new ADC (18-bit to 24-bit)
Digital control of the moving mirror drive using an advanced high speed digital signal processor (DSP) technology
The 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 of 7.1, 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
31. Spectroscopy
Spectroscopy
Polymer shell
Improved instrument design
Compact size
Sample 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-4200 Microscope
FTIR4000 Series
33. Spectroscopy
Spectroscopy
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
DSP
DAC
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)
34. Spectroscopy
Spectroscopy
FT/IR-6100 / 6200 / 6300
FT/IR-600Plus
Polymer shell
Improved instrument design
Compact size
- Upgradeability
- Wide wavenumber range
- Full vacuum capability
- Step scan upgrade
Microscope
FT-Raman
FT/IR-6000 Series Optical design
FTIR6000 Series
35. Spectroscopy
Spectroscopy
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
