Infra Red Spectroscopy and Its Applications

Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared
region of the electromagnetic spectrum, that is light with a longer wavelength and
lower frequency than visible light.
Infrared Spectroscopy is the analysis of infrared light interacting with a molecule.

1. Infrared Spectroscopy and its applications Presented by: Vikram Choudhary M.Pharm 1 st sem Department of Pharmaceutical C hemistry , School of Pharmacy, DAVV , Indore

2. Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light . Infrared Spectroscopy is the analysis of infrared light interacting with a molecule.

3. They are divided into 3 regions Near IR Region Middle IR Region Far IR Region

4. Most of the analytical applications are confined to the middle IR region because absorption of organic molecules are high in this region .

5. When infrared 'light' or radiation hits a molecule, the bonds in the molecule absorb the energy of the infrared and respond by vibrating. IR radiation v anll i n Molecular vibrations

6. Molecules are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds look like spring and b alls (vibration). When internal vibrational energy of molecule matches with energy of extern ally app lied IR, quantized. Molecules absorb IR. A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole moment. Molecule excited from lower to the higher vibrational level. i.e. Increases the amplitude of vibration . Cont’d

7. Molecular V ibrations There are 2 types of vibrations: 1.Stretching vibrations 2.Bending vibrations 1.Stretching vibrations: Vibration or osci illa tion along the line of bond. Change in bond length. Occu rs at higher energy : 400 0-1250 cm -1

8. There are 2 Types of Stretching vibrations a) Symmetrical stretching a) Asymmetrical stretching

9. a) Symmetrical stretching: 2 bonds increase or decrease in length simultaneously. H H C

10. b) Asymmetrical stretching • One bond length is increased and other is decreased. H H C

11. 2. Bending vibrations Vibration or osci l l ation not along the line of bond. These are also ca lle d as deformations . In this, bond angle is altered. O c urs at low energy: 14 00 - 666 cm -1 2 types: In plane bending: sci ss oring , rocking Out plane bending: wagging, twisting

12. a) In plane bending H C H

13. i . Rocking: H C H i i : Scissoring

14. b) Out plane bending i. Wagging : 2 atoms move to one side of the plane. They move up and down the plane. H C H

15. ii) T w i s t i n g : One atom moves above the plane and another atom moves below the plane H C H

16. We can also calculate an approximate value of the stretching vibrational frequency of a bond by treating the two atoms and their connecting bond, to first approximation, as two balls connected by a spring, acting as a simple harmonic oscillator for which the Hooke’s Law may be applied. According to Hooke’s Law , The Stretching frequency is related to the masses of the atom and the force constant(a measure of resistance of a bond to stretching) of a bond by the following equation H ook e ’ s L a w

17. There are basically two types of spectrometers 1.single beam spectrometer 2.double beam spectrometer In a single beam spectrometer the radiations emitted from the source are passed through a cell containing the sample and through the prism which disperses the light. Single beam spectrometers are simple,sensitive and versatile. INSTRUMENTATION OF IR SPECTROSCOPY

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19. The double beam spectrometers are so constructed that the light from the source is split into two beams of equal intensity, one passing through the sample and the other through the reference for compensation. The two beams are recombined on to a common axis and are alternatively focused on to the entrance slit of the monochromator. Dbs are very convenient and hence used in labs ,reserch work and in routine works INSTRUMENTATION OF IR SPECTROSCOPY

20. The main parts of IR spectrometer are as follows:  radiation source  sample cells and sampling of substances.  monochromators  detectors  recorder INSTRUMENTATION OF IR SPECTROSCOPY

21. IR instruments require a source of radiant energy which emit IR radiation which must be : INSTRUMENTATION OF IR SPECTROSCOPY

22. Sources of IR radiations are as follows: GLOBAR : INSTRUMENTATION OF IR SPECTROSCOPY

23. NERNSTGLOWER: INSTRUMENTATION OF IR SPECTROSCOPY

24. For gas samples: The spectrum of a gas can be obtained by permitting the sample to expand into an evacuated cell, also called a cuvette. Gas cell has NaCl windows at the end. For solution sample: Infrared solution cells consists of two windows of pressed salt sealed. Samples that are liquid at room temperature are usually analyzed in pure form or in solution. INSTRUMENTATION OF IR SPECTROSCOPY

25. For S olid S ample : Solids reduced to small particles (less than 2 micron) can be examined as a thin paste or mull. The mull is formed by grinding a 2-5 milligrams of the sample in the presence of one or two drops of a hydrocarbon oil (nujol oil). The resulting mull is then examined as a film between flat salt plates. Another technique is to ground a milligram or less of the sample with about 100 milligram potassium bromide. The mixture is then pressed in an evaluable die to produce a transparent disk. INSTRUMENTATION OF IR SPECTROSCOPY

26. FORE OPTICS Consists of Source, Mirrors, M1,M2 and a Rotating mirrors M1,M2 divides the beam. M alternately allows the s a m p l e b e a m a n d r e f e r e n c e beam to pass through. MONOCHROMATOR Splits the polychromatic radiation to component wavelengths. Make use of prisms or grating or both. Resolution depends on slit width and quality of mirrors. Rock salt prism is generally used in the range of 650-4000cm -1 INSTRUMENTATION OF IR SPECTROSCOPY

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28. Detector T h ermal Non-thermal INSTRUMENTATION OF IR SPECTROSCOPY

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30. There are four types of thermal detector.  Bolometers  Thermocouple and thermopile  Pyro electric detector  Golay Cell INSTRUMENTATION OF IR SPECTROSCOPY

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32. THE RECORDER The amplified signal is recorded by an Pen Recorder. This instrument optical y balances out differential between 2 beams. This kind of Instrument is cal ed Optical nul recording Spectrometer. More sophisticated Instruments are cal ed Ratio- recording Instruments. In these instruments the intensities of both sample and reference beams are measured and ratioed. INSTRUMENTATION OF IR SPECTROSCOPY

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34. F T - I R • FT-IR stands for Fourier Transform Infrared Spectrometer, the pref erre d method of infrared spectroscopy. • Dispersive infrared spectrometers suffer from several disadvantages in sensitivity, speed and wavelength a c uracy. • An entirely different principle is involved in Fourier Transform infrared spectroscopy, which centres on a Michelson interferometer, so that the method can also be c alle d Interferometric infrared spectroscopy. INSTRUMENTATION OF IR SPECTROSCOPY

35. INSTRUMENTATION OF FTIR

36. 1. Identification of Substances  To compare spectrums.  No two samples will have identical IR spectrum.  Criteria : Sample and reference must be tested in identical conditions, like physical state, temperature, solvent, etc.

37. The “Fingerprint” Region (1200 to 700 cm - 1 ) : Sm all differences in structure & constitution of molecule result in significant changes in the peaks in this region. Hence this region helps to identify an unknown compound.

38. Structural/Functional Components

39. IR Spectrum in Alcohol

40. Computer Search Systems Virtu ally all infrared instrument manufactures now off er computer search systems to assist chemist in identifying compounds from stored infrared spectral data. The position and relative magnitudes of peaks in the spectrum of the analyte are determined and stored in memory to give a peak profile, which can then be compared with profiles of pure compounds stored.

41. Studying Progress of Reactions Observing rate of disappearance of characteristic absorption band in reactants; or Rate of increasing absorption bands in products of a particular product. Eg.: O—H= 3600-3650 cm -1 C=O = 1680-1760 cm -1

42. Detection of Impurities Determined by comparing sample spectrum with the spectrum of pure reference compound. Eg.: ketone impurity in alcohols.

43. Measurement of Paints & Varnishes Measured by ‘reflectance analysis’. Advt: Measure IR absorbance of paints on appliances or automobiles without destroying the surface..

44. Examination of Old Paintings & Artifacts Help to determine fake “masterpieces”. Varnish & paints from old items (statues, canvas, etc.) are analysed by IR spectroscopy. Presence of new paint traces implies the “masterpiece” is fake.

45. In Industry Determine impurities in raw materials (to ensure quality products). For Quality Control checks; to determine the % of required product. Identification of materials made in industrial research labs, or materials of competitors. E.g.: Impurity in bees wax (with petroleum wax)

46. Medical applications Hair: Narcotics in hair Effects of bleaching Effects of UV-radiation Skin: Moisture content Lipid content Effects of cosmetics

47. ADVANTAGES Detection (health condition) Prevention (early diagnosis) Monitoring Diagnosis (under investigation) FT-IR Spectroscopy can be applied for the determination of a biochemical metabolite in biological fluids. FT–IR spectroscopy has been used for the determination of glucose, total protein, urea, triglyceride, cholesterol, and very low density lipoproteins in plasma and serum.

48. Reference s Stuart.B.2004.Infrared Spectroscopy: Fundamentals and Applications, John Wiley and Sons Inc , New York, Pp: 223-240. Upadhyay . A, Upadhyay . K , and Nath . N . 2012. Biophysical Chemistry ( Principles and Techniques). Himalaya Publishing House. Pvt. Ltd, Mumbai. Pp.175-186. Sharma Y. R, “Elementary Organic Spectroscopy” Fifth Edition 2017, Published by: S Schand and Company Limited Holme.D.J & Peck.H . 1998. Analytical Biochemistry, Third Edition, Pearson Education Limited.Pp:37-39. http://www.chem.ucla.edu/~webspectra/irtable.htm l •