FTIR(Fourier transform infrared) spectroscopy
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The document provides an overview of Fourier Transform Infrared (FT-IR) spectroscopy, explaining its principles, advantages, and the differences from dispersive infrared spectrometers. FT-IR utilizes an interferometer for rapid and sensitive measurements, allowing simultaneous collection of all infrared frequencies, which enhances efficiency and accuracy in identifying materials. Sampling techniques for various states of matter (liquid, solid, and gas) are also discussed, along with the instrumental process involved in obtaining infrared spectra.
FTIR(Fourier transform infrared) spectroscopy
- 1. PRESENTED BY:- Preeti Choudhary MSc (Applied Physics) chaudharypreeti1997@gmail.com Theory and principle of FTIR
- 2. What is Infrared Region? Infrared radiation lies between the visible and microwave portions of the electromagneticspectrum. 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.
- 3. 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. According to Principle ofIR, Molecular Vibration takes place as a result of Absorption of IR radiation when – Applied Infrared Frequency = Natural frequency of vibration •Every bond or functional groups requires different frequency for Absorption. Hence characteristics Peak is observed for every functional group or part of the molecule.
- 5. Infrared Spectroscopy For isopropyl alcohol, CH(CH3)2OH, the infrared absorption bands identify the various functional groups of the molecule.
- 7. FT-IR stands for Fourier Transform Infrared, the preferred method of infrared spectroscopy. In infrared spectroscopy, IR radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it is passed through (transmitted). The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample. Like a fingerprint no two unique molecular structures produce the same infrared spectrum. This makes infrared spectroscopy useful for several types of analysis.
- 8. So,what informationcan FT-IR provide? It can identify unknown materials It can determine the quality or consistency of a sample It can determine the amount of components in a mixture
- 9. Superiority of FT-IR Dispersive infrared spectrometers suffer from several disadvantages in sensitivity, speed and wavelength accuracy. Most of the light from the source does not in fact pass through the sample to the detector, but is lost in the narrowness of the focusing slits; only poor sensitivity results. Since the spectrum takes minutes to record, the method cannot be applied to fast processes. Dispersive infrared spectrometers scan over the wavelength range and disperse the light by use of a grating, these spectrometers suffer from wavelength inaccuracies associated with the backlash in the mechanical movements, such as in the rotation of mirrors and gratings. An entirely different principle is involved in Fourier Transform infrared spectroscopy, which centres on a Michelson interferometer, so that the method can also be called interferometric infrared spectroscopy.
- 10. Fourier transform infrared spectroscopyis preferred over dispersive or filter methods of infrared spectral analysis for several reasons: • It is a non-destructive technique. • It provides a precise measurement method which requires no external calibration. • It can increase speed, collecting a scan every second. • It can increase sensitivity. • It has greater optical throughput. • It is mechanically simple with only one moving part.
- 11. Toseparate IRlight, a grating isused. Grating Light source Detector Sample Slit Toselect the specified IRlight, A slit isused. Fixed CCM B.S. Moving CCM IRLightsource 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).
- 12. Dispersive Spectrometer FTIR In order to measure an IR spectrum, the dispersion Spectrometer takesseveral minutes. Also the detector receives only a few % of the energy of original light source. 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.)
- 13. THEORY OF FT-IR: Fourier Transform Infrared (FT-IR) spectrometry was developed in order to overcome the limitations encountered with dispersive instruments. The main difficulty was the slow scanning process. A method for measuring all of the infrared frequencies simultaneously, rather than individually, was needed. A solution was developed which employed a very simple optical device called an interferometer. The interferometer produces a unique type of signal which has all of the infrared frequencies “encoded” into it. The signal can be measured very quickly, usually on the order of one second or so. Thus, the time element per sample is reduced to a matter of a few seconds rather than several minutes.
- 14. Most interferometers employ a beamsplitter which takes the incoming infrared beam and divides it into two optical beams. One beam reflects off of a flat mirror which is fixed in place. The other beam reflects off of a flat mirror which is on a mechanism which allows this mirror to move a very short distance (typically a few millimeters) away from the beamsplitter. The two beams reflect off of their respective mirrors and are recombined when they meet back at the beamsplitter. Because the path that one beam travels is a fixed length and the other is constantly changing as its mirror moves, the signal which exits the interferometer is the result of these two beams “interfering” with eachother. The resulting signal is called an interferogram which has the unique property that every data point (a function of the moving mirror position) which makes up the signal has information about every infrared frequency which comes from the source.
- 17. This means that as the interferogram is measured, all frequencies are being measured simultaneously. Thus, the use of the interferometer results in extremely fast measurements. Because the analyst requires a frequency spectrum (a plot of the intensity at each individual frequency) in order to make an identification, the measured interferogram signal can not be interpreted directly. A means of “decoding” the individual frequencies is required. This can be accomplished via a well-known mathematical technique called the Fourier transformation. This transformation is performed by the computer which then presents the user with the desired spectral information for analysis.
- 18. SAMPLING TECHNIQUES 1.Liquid Samples: Neat sample Diluted solution Liquid cell 2.Solid Samples: Neat sample Cast films Pressed films KBr pellets Mull 3.Gas Samples: Short path cell Long path cell
- 19. The Sample Analysis Process: The normal instrumental process is as follows: 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 (and, ultimately, to the detector). 2.The Interferometer: The beam enters the interferometer where the “spectral encoding” takesplace. The resulting interferogram signal then exits the interferometer. 3.TheSample: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, which are uniquely characteristic of the sample, are absorbed. 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.
- 20. 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 furthermanipulation. Because there needs to be a relative scale for the absorption intensity, a background spectrum must also be measured. This is normally a measurement with no sample in the beam. This can be compared to the measurement with the sample in the beam to determine the “percent transmittance.” This technique results in a spectrum which has all of the instrumental characteristics removed. Thus, all spectral features which are present are strictly due to the sample. A single background measurement can be used for many sample measurements because this spectrumis characteristic of the instrument itself.
- 22. Advantages of FT-IR •Speed: Because all of the frequencies are measured simultaneously, most measurements by FT-IR are made in a matter of seconds rather than several minutes. •Sensitivity: Sensitivity is dramatically improved with FT-IR for many reasons. The detectors employed are much more sensitive, the optical throughput is much higher which results in much lower noise levels, and the fast scans enable the co addition of several scans in order to reduce the random measurement noise to any desired level (referred to as signal averaging). •Mechanical Simplicity: The moving mirror in the interferometer is the only continuously moving part in the instrument. Thus, there is very little possibility of mechanical breakdown.
- 23. • Internally Calibrated: These instruments employ a HeNe laser as an internal wavelength calibration standard. These instruments are self-calibrating and never need to be calibrated by the user.
- 24. REFERENCES :- • Introduction to Fourier Transform Infrared Spectrometry By Thermo Nicolet Corporation • An article onFTIR SAMPLING TECHNIQUES by Hue Phan. TN.101 • Instrumental Methods Of Chemical Analysis by Gurdeep R. Chatwal & Sham K.Anand • P. R. Griffiths and J. A. de Haseth, Fourier-Transform Infrared Spectroscopy, Wiley- Interscience, New York, Chichester,Brisbane, Toronto, Singapore,1986 • FTIR Spectroscopy By Jorge. E. Perez and Richard T. Meyer CIC •Photonics, Inc. 3825 Osuna Rd. NE Ste. 6 & 7. Albuquerque, NM 87105.