1. Satish Pradhan Dnyanasadhana College, Thane-400604
Satish Pradhan Dnyanasadhana College, Thane Department of Chemistry M.Sc. Analytical Chemistry Sem-II 1.1 General introduction to spectroscopic methods

2. Syllabus
1.1 General introduction to spectroscopic methods:, Recapitulation Of Basic Concepts, general instrumentation: sources, wavelength selectors, sample containers, radiation transducers, signal processors and read out system, fiber optics, types of optical instruments, Fourier transform optical instruments.[5L]
1.2 Molecular ultra violet and visible spectroscopy:
factors affecting molecular absorption, types of transitions, pH, temperature, solvent, effect of substituents, Derivative and dual wavelength spectroscopy, applications including simultaneous determinations.

3. Recapitulation Of Basic Concepts

4. ?
What is Spectroscopy?

5. What is Electromagnetic Radiation
Electromagnetic radiation, or light, is a form of energy whose behavior is described by the properties of both waves and particles. The optical properties of electromagnetic radiation, such as diffraction, are explained best by describing light as a wave

6. Energy Increases
Wavelength Decreases
Electromagnetic Spectrum

7. W A V E L N G T h I C R S
Energy Increases

8. Properties of electromagnetic radiation
Frequency: The number of oscillations of an electromagnetic wave per second (n).
Wavelength: The distance between any two consecutive maxima or minima of an electromagnetic wave (l).
Wave number:The reciprocal of wavelength (–n).

9. GENERAL INSTRUMENTATION
Radiation Source
Wavelength selector
Sample Cell
Detector
Amplifier
Read Out Device

10. In this energy is supplied by photons.
Sources of Energy
In this energy is supplied by photons.
Absorption
Spectroscopy
Scattering
Techniques

11. Thermal or chemical energy source . luminescence spectroscopy
Sources of Energy
Thermal or chemical energy source .
Emission
Spectroscopy
luminescence spectroscopy

12. Type of Source
A continuum source emits radiation over a wide range of wavelengths, with a relatively smooth variation in intensity as a function of wavelength
Line sources, on the other hand, emit radiation at a few selected, narrow wavelength ranges

13. The most common sources of thermal energy
flames
Flame sources use the combustion of a fuel and an oxidant such as acetylene and air, to achieve temperatures of 2000–3400 K.
plasmas
Plasmas, which are hot, ionized gases, provide temperatures of 6000–10,000 K.

14. Exothermic reactions also may serve as a source of energy
Chemical Sources of Energy
Exothermic reactions also may serve as a source of energy
In chemiluminescence the analyte is raised to a higher-energy state by means of a chemical reaction, emitting characteristic radiation when it returns to a lower-energy state
When the chemical reaction results from a biological or enzymatic reaction, the emission of radiation is called bioluminescence.
Commercially available “light sticks” and the flash of light from a firefly are examples of chemiluminescence and bioluminescence, respectively.

15. Electromagnetic spectrum
Radiation Source
H2 and D2 lamp
Wavelength region
continuum source from 160–380 nm
Useful for UV
molecular absorption
UV Spectroscopy

16. Electromagnetic spectrum
Radiation Source
tungsten lamp
Wavelength region nm
Useful for
Vis molecular absorption
Visible Spectroscopy

17. Electromagnetic spectrum
Radiation Source
Xe arc lamp
Wavelength region
continuum source from 200–1000 nm
Useful for
Vis molecular absorption
molecular fluorescence
Spectroscopy

18. Electromagnetic spectrum
Radiation Source
Nernst glower
Wavelength region
continuum source from 0.4–20 um IR
Useful for
Vis molecular absorption
molecular absorption
Spectroscopy

19. Useful for Sr.No. Radiation Source Wavelength region 1 H2 and D2 lamp
continuum source from 160–380 nm
UV molecular absorption 2
tungsten lamp
continuum source from 320–400 nm
Vis molecular absorption 3
Xe arc lamp
continuum source from 200–1000 nm
molecular fluorescence 4
Nernst glower
continuum source from 0.4–20 um
IR molecular absorption 5
Globar
source from 1–40 um 6
Nichrome wire
continuum source from 0.75–20 um 7
hollow cathode lamp
line source in UV/Vis nm
UV/Vis atomic absorption 8
Hg vapor lamp 9
laser line source
UV/Vis nm
atomic and molecular absorption, fluorescence and scattering

21. Wavelength selectors
Absorption filters work by selectively absorbing radiation from a narrow region of the electromagnetic spectrum.
Commercially available absorption filters provide effective bandwidths from 30–250 nm. The maximum throughput for the smallest effective band passes, however, may be only 10% of the source’s emission intensity over that range of wavelengths.
Interference filters uses constructive and destructive interference to isolate a narrow range of wavelengths. A simple example of an absorption filter is a piece of colored glass. A purple filter, for example, removes the complementary color green from 500–560 nm.
Interference filters are more expensive than absorption filters, but have narrower effective bandwidths, typically 10–20 nm, with maximum throughputs of at least 40%.

22. Wavelength Selection Using Monochromators One limitation of an absorption or interference filter is that they do not allow for a continuous selection of wavelength.
If measurements need to be made at two wavelengths, then the filter must be changed in between measurements. A further limitation is that filters are available for only selected nominal ranges of wavelengths.
An alternative approach to wavelength selection, which provides for a continuous variation of wavelength, is the monochromator.
The construction of a typical monochromator is shown in Figure Radiation from the source enters the monochromator through an entrance slit. The radiation is collected by a collimating mirror, which reflects a parallel beam of radiation to a diffraction grating. The diffraction grating is an optically reflecting surface with

23. WAVELENGTH SELECTORS LIGHT DISPERSING DEVICES
Filters
Absorption Filters
Interference Filters
MONOCHROMATORS
Prism
Monochromator
Grating
Interferometers

24. 1.Filters 24
MCL
PCL

25. 2. PRISM MONOCHROMATOR FOCUSING LENS COLLIMATING LENS PRISM
LAMBDA-1
LAMBDA-2
PRISM
ENTRANCE SLIT
EXIT SLIT
PRISM MONOCHROMATOR

26. PRISM MONOCHROMATOR

27. GRATING MONOCHROMATOR

28. GRATING MONOCHROMATOR
MAGINIFIED VIEW
ENLARGED VIEW
GRATING MONOCHROMATOR

29. Interferometers as wavelength selector In FTIR Spectroscopy
Interferometer: A device that allows all wavelengths of light to be measured simultaneously, eliminating the need for a wavelength selector
interferometer simultaneously allows source radiation of all wavelengths to reach the detector. Radiation from the source is focused on a beam splitter that transmits half of the radiation to a fixed mirror, while reflecting the other half to a movable mirror.
The radiation recombines at the beam splitter, where constructive and destructive interference determines, for each wavelength, the intensity of light reaching the detector.
As the moving mirror changes position, the wavelengths of light experiencing maximum constructive interference and maximum destructive interference also changes.
The signal at the detector shows intensity as a function of the moving mirror’s position, expressed in units of distance or time. The result is called an interferogram, or a time domain spectrum. The time domain spectrum is converted mathematically, by a process called a Fourier transform, to the normal spectrum (also called a frequency domain spectrum) of intensity as a function of the radiation’s energy.

30. Interferometers as wavelength selector
In FTIR Spectroscopy
Source
Beam splitter
Moving
Mirror
Sample
Detector
Fixed mirror

31. Sample cell

32. Detectors
The first detector for optical spectroscopy was the human eye, which, of course, is limited both by its accuracy and its limited sensitivity to electromagnetic radiation.
Modern detectors use a sensitive transducer to convert a signal consisting of photons into an easily measured electrical signal.
Ideally the detector’s signal, S, should be a linear function of the electromagnetic radiation’s power, P,
S = kP + D
where k is the detector’s sensitivity, and D is the detector’s dark current, or the background electric current when all radiation from the source is blocked from the detector.

33. Transducer
A device that converts a chemical or physical property, such as pH or photon intensity, to an easily measured electrical signal, such as a voltage or current.

34. Transducer
Photon Transducer
Thermal Transducer

35. PHOTOCELL DETECTOR
(--) D D G C E- G B A +

36. PHOTO TUBE DETECTOR
Photo Cathode
Collector Anode -
AMPLIFIER RECORDER

38. Thermal Transducers
Infrared radiation generally does not have sufficient energy to produce a measurable current when using a photon transducer.
A thermal transducer, therefore, is used for infrared spectroscopy.
The absorption of infrared photons by a thermal transducer increases its temperature, changing one or more of its characteristic properties.

39. The pneumatic transducer, for example, consists of a small tube filled with xenon gas equipped with an IR-transparent.
window at one end, and a flexible membrane at the other end. A blackened surface in the tube absorbs photons, increasing the temperature and, therefore, the pressure of the gas. The greater pressure in the tube causes the flexible membrane to move in and out, and this displacement is monitored to produce an electrical signal.

40. Signal processor :
A device, such as a meter or computer, that displays the signal from the transducer in a form that is easily interpreted by the analyst. .

41. COMPUTERS EQUIPPED WITH DIGITAL ACQUISITION BOARDS
SIGNAL PROCESSOR
ANALOG METERS
OR DIGITAL METERS
RECORDERS
COMPUTERS EQUIPPED WITH DIGITAL ACQUISITION BOARDS

42. What is function of Signal processer ?
The electrical signal generated by the transducer is sent to a signal processor where it is displayed in a more convenient form for the analyst.
The signal processor also may be used to calibrate the detector’s response, to amplify the signal from the detector, to remove noise by filtering, or to mathematically transform the signal.

43. membrane displacement
Detector
Class
Wavelength Range
Output Signal
PHOTOTUBE
PHOTON
200–1000 nm
current
PHOTO MULTIPLIER
110–1000 nm
SI PHOTODIODE
250–1100 nm
PHOTOCONDUCTOR
750–6000 nm
change in resistance
PHOTOVOLTAIC CELL
400–5000 nm
current or voltage
THERMOCOUPLE
THERMAL
0.8–40 mm
voltage
THERMISTOR
PNEUMATIC
0.8–1000 mm
membrane displacement
PYROELECTRIC
0.3–1000 mm

44. Types Of
Optical Instruments

45. 1. Instrument: Single Beam Colorimeter
Monochromatic light
Photocell /PMT detector
Read Out
Device
U.V.Light & visible light
Filter or
Monochromator

46. 2. Atomic Absorption Spectrophotometer
Rotating Chopper
Hollow
Cathode
Lamp
P.M.T.Detector
Flame
Amplifier
Read Out
Grating
Power
Supply
Sample Solution

47. 3. Flame Photometer Slit Collimating Mirror P.M.T.Detector Amplifier
Read Out
Fuel
Oxidant
Prism Monochromator
Sample Solution

48. 2. Instrument: Single Beam Fuorimeter
Monochromatic light
U.V.Light & visible light
Primary filter
Secondary filter
Photocell /PMT detector
Read Out Device

49. Turbidimeter 4 visible light Filter Photocell Detector Read Out Device
Sample Cell
visible light
Filter
Technique is used when concentration of suspended particles are high
In this intensity of transmitted light is measured

50. Nephelometer 5 visible light Light Trap Photocell Detector Sample Cell
Graduated Disc
Collimating Lens
Light Trap
visible light
Photocell Detector
Technique is used when concentration of suspended particles are less
In this intensity of scattered light is measured
Sample Cell
Read Out Device

51. Fourier transform optical instruments

52. Fourier Transform- Infrared Spectroscopy (FT-IR)
The mid-IR region covers the range from 4000 to 400 cm-1. The basic principle of the IR technique is that various organic functional groups absorb infrared light at specific wavelengths. Thus, since every organic molecule has a unique chemical composition, it also has a unique infrared spectrum.
Biological samples are composed of proteins, carbohydrates, lipids and nucleic acids.
Since these molecules contain functional organic groups, the IR spectrum consists of bands from all these components.
The infrared spectrum is very complex, and it contains a large amount of information. To evaluate the data, it is necessary to use multivariate statistical analysis.

53. Energy for Atom and Molecule
Electronic Energy
Electronic Energy
Atom
Atom
Rotational Energy
Vibrational Energy

54. CH3----------------- CH3
Rotational Energy
CH CH3
Motion of molecule from the centre of joining the nuclei

55. Bond length 154 pm, Stretching
Vibrational Energy
Bond length 154 pm,
Stretching
10 pm.
For a C-C bond with a bond length of 154 pm, the variation is about 10 pm.

56. C C C 4o Bending 10 pm Vibrational Energy
For C-C-C bond angle a change of 4o is typical. This moves a carbon atom about 10 pm.

57. Regions of Absorption
U.V. nm
Visible nm