FTIR fourier transform infrared spectroscopy
- 1. FTIR Spectroscopy Fourier Transform Infrared spectroscopy (FTIR) is an analytical technique used to identify organic, inorganic, polymeric and other materials. Also called as FTIR Analysis It uses Infrared light to scan test samples and observe chemical properties. Performed by a Fourier Transform Infrared spectrophotometer as shown
- 2. Introduction • FTIR stands for Fourier Transform Infra Red , it is a type of infra-red spectroscopy. In infrared spectroscopy, IR radiations is passed through a sample. Some of the radiations are absorbed by the sample and some of it is passed through • The name FTIR is given due to Fourier Transformation which is performed by a computer. • It can measure all of the IR frequencies simultaneously rather then individualy • All solids, liquid, as well as gas samples are analyzed by FTIR Spectroscopy
- 3. Principle 1. The IR energy is emitted from IR source & passed through Interferometer 2. The Interferometer use reference laser for wavelength calibration 3. Then enter the sample compartment where it is absorbed 4. Then passe to detector for final measurements that gives output in the form of Interferogram 5. Then FT calculations performed by a computer and infrared spectrum is obtained.
- 5. Instrumentation of FTIR System The basic components of FTIR system consists of; 1. Radiation Source 2. Interferometer 3. Detector
- 6. 1. Infrared Source 1.Incendecent lamp 2.Nernst Glower 3.Globar Source4.H.P mercury Arc 0.78-2.5 micro - meter Near-IR at 1100K (W) 1-50 micro - meter mid-far IR at 1500K (Oxide ) 50-300 micro - meter far-IR (Plasma) 1-50 micro - meter mid-far IR at 1500K (SiC rod)
- 7. Interferometer An Interferometer is an optical equipment, invented by Albert Abraham Michelson (received Noble prize in 1907) Commonly known as Michelson Interferomete The basic components of interferometer are; 1. A Beam-splitter 2. A Fixed mirror 3. A Moving mirror
- 8. Beam Splitter Beam-splitter is a semi-reflecting optical device that 50% of the light from the IR source is transmitted while remaining 50% is reflected. It is either a partially silvered mirror or a thin film of germanium (Ge) sandwiched between two KBr plates. Interferometer
- 9. Mirrors • Infrared light received from the source is split into two beams by beam splitter. One beam (wave) is reflected to the flat Fixed mirror, while other is transmitted to the Moving mirror. • The two beams are reflected backe by their their respective mirrors to recombine at beam-splitter , again form one beam which is transmitted to the detector through Interferometer
- 10. Detector A device that detects the absorbance of the beam through the sample is called detector. • The detectors used in FTIR spectrophotometer should be such that it's speed & accuracy matches with the speed & sensitivity of the instrument. • These detectors are classified into two categories; 1. Thermal Detector 2. Quantum mechanical Detector
- 11. Comparison Thermo Detector Quantum Mechanical Detector • A thermo detector uses the infrared beam as heat. • Operates by detecting changes in temperature of an absorbing material • A Quantum mechanical detector uses the IR beam as light and provide for more sensitive detector. Example Example Pyroelectric detector: Deuterated Triglycine Sulphate (DTGS) Photon- sensitive semiconducting detector: Mercury cadmium telluride (MCT)
- 12. Interferogram • The visual output of the detector formed by the interference of two beams or waves in interferometer is called as Interferogram • The detected interferogram cannot be directly interpreted Interference Interferogram • The joining or recombination of beams at beam splitter after splitting is called as " Interference "
- 13. Interference Zero Path Difference Beams (waves) can interfere either constructively or destructively depending on the Zero path difference (ZPD)and Optical path difference (OPD) Optical Path Difference If the fixed and moveable mirrors are at equal distance from the beam splitter, the distance travelled by the two beams after being reflected by these mirrors is the same, known as ZPD. If the fixed and moveable mirrors are not at equal distance from the beam splitter, the distance travelled by the two beams after reflection from the mirrors is not same. This condition is called as OPD.
- 14. Constructive Interference Destructive Interference Interference If the two beams of radiation recombining at the beam splitter are in phase (ZPD), are said to be interfere constructively and intense light beam is detected by the detector. If the two beams of radiation recombining at the beam splitter are out phase (ZPD), are said to be interfere detructively and no light beam is detected by the detector.
- 15. Interference
- 16. Fourier Transformation "Fourier Transformation is a mathematical operation which is performed by a computer attached to FTIR spectrophotometer." • Because interferogram which is a time-domain spectrum cannot interpreted as such • Fourier Transformation coverts it into a frequency-domain spectrum.
- 17. Spectrum The spectrum is given by the computer as as percent transmittance (%T) against wavenumber ( frequency) . Spectrum The transmittance spectrum is converted into absorbance (A) spectrum as; Where • I is the intensity measured with the sample • Io is the intensity measured without sample
- 18. Calibration of Spectrum Every FTIR- Spectrophotometer is equipped with He-Ne laser which serve as internal interference for the calibration of wavenumber scale.
- 19. Summary of FTIR Spectroscopy
- 21. Sample Preparation Infrared spectra can be obtained for ; 1. Solids 2. Liquid 3. Gases • The preparation of samples is often the most challenging task of IR spectroscopy. • Since almost all substances absorb IR radiation at some wavelength and solvents must be chosen carefully for the wavelength region and sample of
- 22. Solid Sampling Spectra of solids are obtained as Alkali halide discs (KBr) or mulls. Alkali halide discs • A milligram or less of the fine ground sample mixed with about100mg of dry KBr powder in a morter. • The mixture compressed in a die to form transparent disc. • And then place in a holder and fit into FTIR spectrophotometer.
- 23. Solid Sampling Mull Technique • Mull is obtained by grinding a few milligrams of powdered sample by a morter or pulverizing equipment. • A few drops of the non-volatile mineral oil (Nujol, or liquid paraffins ) added to form a paste. • Use a syringe to apply this paste to an IR transparent window KBr plates. • This is done with Perkin elmer FTIR spectrometer.
- 24. Solid Sampling 1.Grind the entire sample 3. Add binder (if required) 2. Weigh the sample 4. Mix for 2 minutes 5. Add a pellet film 6. Introduce an Al cup 7. Fill the mixture 9. Perfect pellet 8. Press the mixture
- 25. Liquid Sampling • Liquid Samples are obtained as liquid films sandwiched between two NaCl plates. • Samples that are liquid at room temperature are usually put with no preparation into rectangular cell made up of NaCl , KBr etc and IR spectra is obtained directly .
- 26. Gas Sampling Gas samples are examined after removal of water vapours by using Gas Cell Gas Cell • A gas sample cell consists of glass/metal cylinder of 10cm and is closed with aappropriate window materials (NaCl, KBr) and equipped with valves for introduction of the sample (gas). • Multipass cell is also used. Gas sample cell Multipass cell
- 27. Fourier Transform Infrared Spectrophotometer • FTIR spectrophotometer obtains an infrared spectra by collecting interferogram of a sample using an interferometer & performs a Fourier transform to obtain a spectrum • Sampling rates are controlled by internal independent reference He - Ne laser focused on a separate detector
- 28. Advantages 1. Simple mechanical design 2. Universal technique 3. Sensitive,fast & easy 4. Relatively inexpensive & provide useful information 5. Sensitive to molecules anything that contain "Chemical bonds" 6. Majority of molecules absorb IR light making it a useful tool.
- 29. Disadvantages 1. Cannot detect atoms or monoatomic ions as there is no chemical bonding 2. Cannot detect Homo - diatomic molecules like N2 or O2 3. Aqueous solutions are very difficult to analyze as water is a strong IR absorber 4. Complex mixture samples give rise to complex spectra 1. Identification of organic compounds 2. Structure determination 3. Study of chemical reactions 4. Study of Keto - enol Tautomerism 5. Detection of impurities in a compound 6. Conformational analysis