UV-Visible spectroscopy

here we can get information about electromgnetic radiation, colorimetry and ultraviolet visible spectroscopy

1. UV-Vis Spectroscopy

2. EMR = Electromagnetic Radiations Radio waves Microwaves Infrared radiation Visible light Ultraviolet radiation X-rays Gamma rays

3. EMR = Electromagnetic Radiations

4. EMR = Electromagnetic Radiations

5. WAVELENGTH

6. EMR AS PER WAVELENGTH & FREQUENCY

7. FREQUENCY

8. ULTRAVIOLET RADIATIONS WAVELENGTH (nm)

9. VISIBLE RADIATION WAVENLENGTH (nm)

10. UV-Vis Wavelengths

11. COLORIMETER USED TO ANALYZE COLORED SOLUTIONS

12. Dispersion of light

13. ABSORPTION & TRANSMISSION

14. COLORIMETER Vs UV-Vis Spectrophotometer COLORIMETER - Only colored solutions can be analyzed UV-Vis spectroscopy - Both colored and colorless solutions can be analyzed

15. ELECTRONIC TRANSITION Electronic transitions take place when electrons in a molecule ar e excited from one energy level to a higher energy level. The energy change provides information on the structure of a molecule and determines many molecular properties

16. HIGHER ENERGY LEVEL OR EXCITED STATE LOWER ENERGY LEVEL OR GROUND STATE ELECTRONS

17. ELECTRONS INVOLVED IN ELECTRONIC TRANSITION Sigma electrons (Bonding electrons) Pi electrons (Bonding electrons) n electrons (Non bonding electrons)

18. CHROMOPHORES

19. BEER-LAMBERT’S LAW Johann Heinrich Lambert August Bee r

20. The absorbance is inversely proportional to the transmittence of the solution

21. BEER’S LAW Absorbtion of radiation is directly proportional to concentration of solution A α c …...Eqn. 1

22. LAMBERT’S LAW Absorbtion of radiation is directly proportional to path length of solution A α l …...Eqn. 2

23. DEFINITION The Beer-Lambert law states that the quantity of light absorbed by a substance dissolved in a fully transmitting solvent is directly proportional to the concentration of the substance and the path length of the light through the solution.

24. From eqn. 1 & 2 A α cl A = εcl

25. A = εcl A = Absorbance ε = Molar absorptivity or Molar extinction coefficient or Molar absorption coefficient C = Concentration l = Path length (cm)

26. DERIVATION OF LAW A spectrophotometer is an apparatus that measures the intensity, energy carried by the radiation per unit area per unit time, of the light entering a sample solution and the light going out of a sample solution. The two intensities can be expressed as transmittance: the ratio of the intensity of the exiting light to the entering light or percent transmittance (% T ) . Different substances absorb different wavelengths of light. Therefore, the wavelength of maximum absorption by a substance is one of the characteristic properties of that material. A completely transparent substance will have I t = I and its percent transmittance will be 100. Similarly, a substance which allows no radiation of a particular wavelength to pass through it will have I t = 0, and a corresponding percent transmittance of 0.

27. Deviations to the law The Beer-Lambert law maintains linearity under specific conditions only. The law will make inaccurate measurements at high concentrations because the molecules of the analyte exhibit stronger intermolecular and electrostatics interactions which is due to the lesser amount of space between molecules. This can change the molar absorptivity of the analyte.

28. Applications Generally, it can be used to determine concentrations of a particular substance, or determine the molar absorptivity of a substance.

29. UV-Vis spectrophotometer Single beam UV-Vis spectrophotometer (only sample can be placed) Double beam UV-Vis spectrophotometer (Both sample & reference can be placed)

30. Sample e.g. height of the boy ??????????????

31. Reference e.g. boy of 6 feet

32. On comparing with reference sample’s information can be obtained REFERENCE SAMPLE 6 FEET 4 FEET

33. INSTRUMENTATION Light source Collimator Monochromator Slit (wavelength selector) Sample holder / cuvette Mirror (beam splitter, reflecting mirror & grid mirror) Detector Recorder

34. Light source Halogen lamp Deuterium lamp Xenon lamp Xenon flash lamp Low pressure mercury lamp Many spectrophotometers uses a halogen lamp for the visible range and a deuterium lamp for the ultraviolet range according to the wavelength requirement.

35. Collimator Also called collimating lens A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays)

36. Collimating lens

37. Monochromator Converts polychromatic light to monochromatic light of specific wavelength Mono = single Poly = many Chrome = color

38. Slit - Allows a specific wavelength to pass through it

39. Sample holder / cuvette

40. Mirror Beam splitter Reflecting mirror Grid mirror

41. GRID MIRROR It collects all radiations and send in one direction

42. DETECTORS

43. Silicon Photodiode

44. RECORDER

45. GRAPH GRAPH

46. APPLICATIONS

47. 6. Spectrophotometric titrations

48. Spectrophometric titration - During a spectrophotometric titration, we monitor changes in absorbance to determine the equivalence point. The end point is where the graph is discontineous.

49. SPECTROPHOTOMETRIC CURVES

50. 7. Single component & multicomponent analysis

51. TAPAN KUMAR MAHATO [email protected]