Ir spectroscopy

The powerpoint contains principle,instrumentation and application of IR and FTIR

1. IR SPECTROSCOPY Mr. Shinde GANESH SHASHIKANT PRAVARA RURAL COLLEGE OF PHARMACY, PRAVARANAGAR Department of Pharmaceutical Chemistry

2. Spectroscopy Method of “Seeing the unseeable” using electromagnetic radiation to obtain information about atoms and molecules that are too small to see. Atoms Molecules

3. Spectroscopy is an instrumentally aided study of the interactions between matter (sample being analyzed) and energy (any portion of the electromagnetic spectrum) EMR ANALYTE SPECTROPHOTOGRAPH 1.UV-Visible radiations--------excitation of electrons---------UV-visible spectrum 2.IR-radiations------------------vibration changes in electrons--------IR spectrum 3.Radio frequency---------------spin rotational changes-------------N.M.R spectrum Conc. should be lower

4. IR spectrophotometry Energy of molecule = Electronic energy+ Vibrational energy + Rotational energy IR spectroscopy is concerned with the study of absorption of infrared radiation, which causes vibrational transition in the molecule. Hence, IR spectroscopy also known as Vibrational spectroscopy. IR spectra mainly used in structure elucidation to determine the functional groups.

5. IR region: Most of the analytical applications are confined to the middle IR region because absorption of organic molecules are high in this region. Sub divided into Near infrared region 0.8-2.5 µ(12,500-4000 cm- 1 ) Main infrared region 2.5-15 µ(4000-667cm- 1 ) Far infrared region 15-200 µ(667-50 cm -1 )

6. Principle of IR spectroscopy Molecules are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds like like spring and balls (vibration) This characteristic vibration are called Natural frequency of vibration.

7. When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules and when, Applied infrared frequency = Natural frequency of vibration Then, Absorption of IR radiation takes place and a peak is observed. Different functional groups absorb characteristic frequencies of IR radiation. Hence gives the characteristic peak value. Therefore, IR spectrum of a chemical substance is a finger print of a molecule for its identification.

8. Criteria for a compound to absorb IR radiation Correct wavelength of radiation Change in dipole moment 1. Correct wavelength of radiation: A molecule to absorb IR radiation, the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation.

9. 2. Change in dipole moment A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole A molecule is said to have an electric dipole when there is a slight positive and a slight negative charge on its component of atoms.

10. Molecular vibrations There are 2 types of vibrations: Stretching vibrations Bending vibrations Stretching vibrations: Vibration or oscillation along the line of bond Change in bond length Occurs at higher energy: 4000-1500 cm -1 (1250 cm -1 ) 2 types: Symmetrical stretching Asymmetrical stretching

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

12. b) Asymmetrical stretching I n Asymmetrical Stretching , one bond length is increased and other is decreased. H H C

13. 2. Bending vibrations Vibration or oscillation not along the line of bond These are also called as deformations In this, bond angle is altered Occurs at low energy: 1400-666 cm -1 2 types: In plane bending: scissoring, rocking Out plane bending: wagging, twisting

14. a) In plane bending Scissoring: This is an in plane blending 2 atoms approach each other Bond angles are decrease H H C C

15. Rocking: Movement of atoms take place in the same direction. H H C C

16. b) Out plane bending i. Wagging: 2 atoms move to one side of the plane. They move up and down the plane. Twisting: One atom moves above the plane and another atom moves below the plane. H H C C H H C C

17. Types of Molecular Vibrations Stretching Vibrations : in which bond length changes that require more energy. Bending Vibrations : in which bond angle changes that require less energy. Asymmetrical stretching Symmetrical stretching Rocking Scissoring Twisting Wagging

18. IR spectra

19. Sampling techniques 21

20. Sampling techniques Sample preparation is the most important part in IR spectral analysis, Sample should be transparent to IR radiations so it allows the radiations to pass through them Hence the salts like KBr , NaCl , AgCl are used for mixing of sample in order to obtain the accurate IR spectrum of a sample with good intensity, sharp peaks and high resolution.

21. 1) Solid samples : Mull technique Pressed pellet technique Solids run in solutions Solid film 2 ) Liquid samples 3) Gaseous sample 23 Sampling techniques

22. Mull technique Grinding 2-5 mg of sample in smooth agitate mortar. Powdered sample + Nujol oil (mineral oil) paste Paste between the two plates of salt. The oil has few absorption bands at 2857, 1449 and 1389 cm -1 The particle size must 1 -2 micron. Nujol agent (mineral oil) used in this techniques are : High boiling petroleum, Halocarbon oil, perfluorokerosene 24

23. Pressed pellet technique: In this technique, a small amount of finely ground solid sample is mixed with 100 times its weight of potassium bromide and compressed into a thin transparent pellet using a hydraulic press. These pellets are transparent to IR radiation and it is used for analysis . 1mg Sample+ 100mg KBr powder 25

24. Solids films : Amorphous solid samples melted between salt plates allowed to form solid film. For qualitative purpose. Solids run in solution Solid + suitable solvent 🡪 solution Kept in cells for liquids Solvents- non associated solvents- CS2, CCl4, 26

25. Liquid sample : 27

26. Liquid sample : Liquid samples are usually handled pure without mixing them with any solvent because all solvents have their own characteristics absorption spectra. For liquid samples highly polished salt ( NaCl , KBr or AgCl ) plates are used. A drop of liquid sample is placed on the face first plate and the second plate is placed on the top to form a uniform film of a sample wipe off the excees liquid spilled from the edge of the plate then place the plates in the sample compartment of spectrophotometer and run the spectrum . 28

27. Gaseous sample : Vapors in specially designed cells. End walls made up of Sodium chloride . A special sample cell is used for the gaseous sample made up of NaCl , KBr with long path length i.e 5 to 10 cm The vapors of gas are placed into the cell and directly place in the path of Infrared radiation 29

28. Instrumentation 30

29. INSTRUMENTATION The main parts of IR spectrometer are as follows : RADIATION SOURCE SAMPLE CELLS AND SAMPLING OF SUBSTANCES MONOCHROMATORS DETECTORS RECORDER

30. INFRARED SOURCES IR instruments require a source of radiant energy which emit IR radiation which must be:

31. Globar source Rod of sintered silicon carbide. (5cm x 5mm). Positive coefficient of resistance. Self starting and electrically heated Enclosed in water cooled brass tube Less intense . Emit Radiation at 5200 cm -1 33

32. Nernst glower Composed of rare earth oxides- zirconium, yttrium and thorium Hollow tube (2-5cm x 1-3mm) Platinum leads at one end Large negative temp. coefficient. Emit radiation 7100 cm -1 over wide range and remains steady over a long period . Disadvantages : Fragile Auxiliary heater Over heating 34

33. Incandescent wire loop Tightly wound spiral of Nichrome wire. No water cooling Less maintenance Less intense than other sources. Tungsten filament lamp Tightly wound spiral of tungsten wire. For near IR Emit radiation 667-4000 cm -1 35

34. Mercury arc For far IR region High pressure Hg arc, enclosed in quartz jacketed tube, at 1 atm Passage of electricity through vapor 🡪 internal plasma sourc IR radiation Emit radiation less than 667 cm -1 36

35. SAMPLE CELL & SAMPLING OF SUBSTANCE

36. Sample holders Constructed of rock salt. Path length is adjusted with Teflon. Filled and emptied with hypodermic needles. Foggy due to moisture. Care: Moisture free samples Fingers should not be come in contact Prevent contamination with silicones 38

37. Sample holders 39

38. Monochromator To select desired frequency from radiation source. Prism monochromator Grating monochromator Material used: Halogen salt 40

39. RADIATION DETECTOR An infrared detector is a detector that reacts to infrared (IR) radiation. It is simply a transducer of radiant energy. Radiant energy Infrared radiations

40. TYPES OF DETECTOR Detector Thermal Non-thermal

41. THERMAL DETECTOR

42. BOLOMETERS Bolometer is derived from a Greek word (bolometron) Bolo = for something thrown Metron = measure It was invented in 1878 by the American astronomer Samuel Pierpont Langley

43. Construction A bolometer consists of an absorptive element, such as a thin layer of metal or thermister . Most bolometers use semiconductor or superconductor absorptive elements rather than metals.

44. Working

45. THERMOCOUPLE AND THERMOPILE Temperature changes Potential difference changes Thermocouples consist of a pair of junctions of different metals; for example, two pieces of bismuth fused to either end of a piece of antimony.

46. Thermopile detectors are voltage-generating devices, which can be thought of as miniature arrays of thermocouple junctions . Cold junction(t2)is kept const. temp and not exposed IR but other junction hot when exposed IR cause increase temp of junction and generatre P.D due to incident IR radiation fall on hot junction .

47. PYRO ELECTRIC DETECTOR Construction: S ingle crystalline wafer of a pyro electric material, such as triglycerine sulphate. Pyro electric Infrared Detectors (PIR) convert the changes in incoming infrared light to electric signals.

48. Below curie temperature Pyro electric materials exhibit electrical polarization. T emperature is altered, the polarization changes . Observed as an electrical signal ( if electrodes are placed on opposite faces of a thin slice of the material to form a capacitor)

49. GOLAY CELL Construction: Small metal cylinder Flexible silvered diaphragm Whole chamber is filled with xenon gas.

50. I.R radiations Metal cylinder and flexible diaphragm Temperature increases Gas is expended and diaphragm deforms detect as a signal

51. NON-THERMAL DETECTORS

52. PHOTOVOLTAIC DETECTOR Infrared radiations Photovoltaic detector( PbS ) Generates a small voltage and increase conductance Detected as a signal

53. WORKING OF IR 55

54. FT-IR

55. 57 INTRODUCTION Absorption of IR radiation by sample, result in vibration transition. Infrared radiation lies between the tfisible and microwave portions of the electromagnetic spectrum. Infrared waves have wavelengths longer than visible and shorter than microwave and have frequencies which are lower than visible and higher than microwaves. IR spectra are mainly used in structure elucidation to determine the groups .

56. PRINCIPLE The Beam Splitter Divides the beam and transmits half of the incoming radiation to the fixed mirror and the other half to the movable mirror . Upon reflection from the fixed and the movable mirror the light is recombined at the beam splitter. The recombination of the radiation is then direct through the sample and focused on the detector on the detector (Pyroelectric detector). When the path difference is ZERO, all the spectral components are in phase and the output is at a MAXIMUM .

57. FT-IR Spectrometer Components Source An optical System which uses interferometer Beam Splitter Stationary mirror Moving mirror Sample Detector

58. Sources: Nernst Glower, Global Source, Tungsten Lamp, Mercury arc. Beam Splitter: It is made up of material which is made up of refractive index For Far Infrared: Mylar film sandwiched between halide plate of low refractive index solid used. For middle IR : Thin film of germanium or silicon deposited on CsI or CsBr or KCl or NaCl. For Near IR: Thin film of ferric oxide deposited on calcium chloride Detector : Pyroelectric Detector is used

59. It consist of two perpendicular mirrors, one of which is Stationary mirror and the other is a movable mirror. The Position of movable mirror is controlled by HeNe Laser. (632.8 nm) Between these two mirrors , set a beam splitter at 45 degree from initial positon of the movable mirror. A parallel beam of radiation from IR source is passed on the mirrors through the beam splitter

60. FTIR Animation video Demonstration

61. FTIR Animation video Demonstration FTIR Animation Video

62. Appl i cat i on For opaque or cloudy samples Analysis of raw materials or finished products. Kinetics reactions on the microsecond time-scale. Analysis of chromatographic and thermogravimetric sample fractions. Micro-Samples. Tiny samples, Such as in forensic analysis Identification of compounds.