Fourier Transform Infrared (FT-IR) Spectroscopy - PowerPoint by qxc16070

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									Spectroscopy
Spectroscopy


               Fourier Transform Infrared
                  (FT-IR) Spectroscopy

                   Theory and Applications
                            THE ELECTROMAGNETIC SPECTRUM
                     GAMMA RAYS       X RAYS     UV    VISIBLE   INFRARED
Spectroscopy
Spectroscopy      Introduction to FTInfrared
                        Spectroscopy

                       infrared spectroscopy?
                What is
                     Theory of FT-IR
                    FT-IR Advantages?
                 New FT/IR4000-6000Series
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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.
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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.
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                             Infrared Spectroscopy
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               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
               Energy levels in Infrared Absorption
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                                                                                     Excited
                                                                                      states
               hn

                                  Infrared Absorption and
                                  Emission
                                             h(n2 - n1)
                        n                    (overtone)
                                 h(n1 -                          h(n1 - n0)
                        n
                        3
                                 n0 )                                                 Ground
                        n
                        2
                                                                                   (vibrational)
                        n
                        1
                                                                                       states
                        0

                    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.
                         Infrared Spectroscopy
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Spectroscopy


               A molecule can be characterized (identified) by its molecular
                vibrations, based on the absorption and intensity of specific
                                   infrared wavelengths.
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                        Infrared Spectroscopy
               For isopropyl alcohol, CH(CH3)2OH, the infrared absorption
                bands identify the various functional groups of the molecule.
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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.
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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.
Spectroscopy
Spectroscopy   Comparison Beetween Dispersion Spectrometer
                               and FTIR
                     To separate IR light, a grating is used.
                                                                                      Detector           Dispersion
               Grating
                                                                   Slit                                  Spectrometer
                                                                                                       In order to measure an IR spectrum,
                                                                                                       the dispersion Spectrometer takes
                                                                           Sample                      several minutes.
                                                                                                       Also the detector receives only
                                                                                                       a few % of the energy of
                                                                                                       original light source.
                                               To select the specified IR light,
                    Light source               A slit is used.



                          Fixed CCM                                 An interferogram is first made
                                                                    by the interferometer using IR        FTIR
                                                                    light.                             In order to measure an IR spectrum,
                                                                                         Detector      FTIR takes only a few seconds.
                                                                                                       Moreover, the detector receives
                                                                                                       up to 50% of the energy of original
                                   B.S.                                                                light source.
                                                                                                       (much larger than the dispersion
                                                                                                       spectrometer.)
                                                                            Sample


               Moving CCM
                                                     The interferogram is calculated and transformed
                             IR Light source         into a spectrum using a Fourier Transform (FT).
Spectroscopy
Spectroscopy
               The Principles of FTIR Method
                                       Interferogram
                                        is made by an interferometer.




                                                                                      Sample

                                              Interferogram
                                              is transformed
                                              into a spectrum using a FT.



                                                                         Sample
                BKG

                SB                                                          SB


                                                   Sample/BKG
                      3000   2000     1000                                          3000        2000    1000

                             [cm-1]                                                            [cm-1]
                                         %T


                                                                                 IR spectrum
                                               3000        2000         1000      [cm-1]
Spectroscopy
Spectroscopy   IR light source
                        FTIR seminar


                                                   IR Light Source

                        Intensity Distribution and Temperature Dependency versus Wavelength of
                        Black Body Radiation Energy
                        105

                                    6000K
                        104
                                          4000K
                        103

                        102                       2000K

                         10

                                                          1000K
                          1

                       10-1
                                                                      500K

                       10-2
                                                                             300K
                       10-3
                                                                                    200K
                       10-4
                              0.1   0.2       0.5         1       2           5       10   20   50   100
                                                          Wavelength l / mm
Spectroscopy
Spectroscopy            FTIR seminar


                           FT Optical System Diagram

                Light                            He-Ne gas laser
               source

               (ceramic)

                                          Beam splitter
                 Movable mirror

                                                          Sample chamber




                                                                                      (DLATGS)
                                       Fixed mirror
                                                                           Detector
                 Interferometer
Spectroscopy
Spectroscopy                  FTIR seminar


                          Interference of two beams of light

                                                                                                     Movable mirror
               Fixed mirror
               A
               Movable mirror

                                             Same-phase interference
                                             wave shape
                                                                                         -2l         -l     0    l    2l
               Fixed mirror                                                                        Continuous phase shift




                                                                       Signal strength
               B
                                                                                         I
               Movable mirror                Opposite-phase                                  (X)
                                             interference
                                             wave shape

                   Fixed mirror
                   C
                   Movable mirror
                                                                                         -2l        -l     0    l     2l
                                             Same-phase interference
                                0    l       wave shape                D Interference pattern of light
                                                                       manifested by the optical-path
                                                                       difference
Spectroscopy
Spectroscopy         FTIR seminar

                Interference is a superpositioning of waves

               Relationship between light source spectrum and the signal output from interferometer

                                        Light source spectrum            I       Signal output from interference wave
               (a)     Monochromatic
                       light    z   A

                                         Wavenumber     u
                                                                                                            Time t
                                                                       S     I

               (b)     Dichroic light
                               SAz


                                         Wavenumber     u                                                    Time t
                                                                      I(t)
               (c)     Continuous
                       spectrum light
                               b (u)

                                         Wavenumber    u                                                     Time t
                                                                All intensities are standardized.
Spectroscopy
Spectroscopy   FTIR seminar

               Sampling of an actual interferogram



                                       Interferometer interferogram




                                       Output of a Laser interferometer




                                       Primary interferometer interferogram
                                                 that was sampled

                                        Optical path difference x
Spectroscopy
Spectroscopy
                                                        Fourier Transform
               Single strength




                                                               Fourier transform   SB




                                  Optical path difference[x]                        4000    Wavenumber[cm-1]     400

                                 (Interferogram)                                        (Single beam spectrum)



                                   Time axis by FFT                                        Wavenumber
Spectroscopy
Spectroscopy                      FTIR seminar


                                                      Detector Properties


                                                                 MCT
                                                      Operates at the temperatur
                                        1010              of liquid nitrogen
               D* (l, f) (cmHz1/2W-1)




                                        109
                                                                          TGS
                                                             Operates at room temperature



                                        108

                                               4000                                         600
                                                                 Wavenumber[cm-1]
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Spectroscopy
                     FT-IR Advantages and Disadvantages
               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
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                        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.
                          FT-IR Advantages
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                               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.
                          FT-IR Advantages
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Spectroscopy

                              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.
               FT-IR Application Advantages
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Spectroscopy


                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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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.
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.
Spectroscopy
Spectroscopy
                     FT-IR Terms and Definitions

               Apodization - a
               mathematical operation to
               reduce unwanted oscillation   Apodization
               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.
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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.
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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.
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Spectroscopy
                   New Features of FTIR4000-6000Series
               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
Spectroscopy
Spectroscopy
                                FTIR4000 Series
                                                        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



                                Polymer shell
                                Improved instrument design
                                Compact size
                                Sample compartment with
                                same size as a higher class
                                                                      Aperture
                                model




               FT/IR-400 Plus
Spectroscopy
Spectroscopy
                          FTIR4000 Series Purge System
                                    Instrument purge is standard for all models of the FT/IR-4000 Series.
                                          N2gas inlet




                                                                          Control valve

               FT/IR-4000 Series purge design
Spectroscopy
Spectroscopy
                            S/N ratio (Oversampling system)
                                                                                                                                 Accurate mirror drive
                                                                         FT/IR-4000 & 6000 series                                And reduce flutter at
               Voice Coil            Conventional method                                  Voice Coil                             low wavenumber range.
                                                                                                                DAC       DSP




                             Analog circuit                                                                              ADC




                                Pre-amp.                                                                              Pre-amp.



                             Photo coupler                                                                         Photo coupler

                                                                                                                               Clock


                                                                                                                  24-bit AD


                                                                                           HeNe laser
               HeNe laser
                                                                                                          Over sampling method
                             Find the zero crossings, then interpolate
                             a matching set of IR data points.              Reduction of high frequency noise by over sampling with a 16 times greater
                                                                            number of sampling points enables improvement of the S/N ratio.
Spectroscopy
Spectroscopy
                                           FTIR6000 Series
                                                                       - Upgradeability
                                                                       - Wide wavenumber range
                                                                       - Full vacuum capability
                                                                       - Step scan upgrade
               FT/IR-6100 / 6200 / 6300
                                                  Microscope

                                           FT-Raman




                                          Polymer shell
                                          Improved instrument design
                                          Compact size




                  FT/IR-600Plus




                                                                         FT/IR-6000 Series Optical design
Spectroscopy
Spectroscopy
                    FTIR6000 Series Purge/Vacuum System
               N2gas inlet              Instrument purge is standard for all models of the FT/IR-6000
                                        Series.




                                                                    Purge control valve – front side




                FT/IR-6000 Series purge design

								
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