بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم

2. Marine Analytical Chemistry MC 361 (Chem 312)

3. Contents • Introduction to Spectroscopy • Concept of Spectroscopy • Infrared Absorption • Ultraviolet Molecular Absorption Spectroscopy • Colorimetry (Spectrophotometry) • Emission Spectrography (Flame Photometery) • Total Organic Carbon (TOC)

4. Chapter 11-Introduction to Spectroscopy • The Interaction between energy and matter: • In case of visible light

5. In general

6. Wavelength range

7. What is Radiant Energy? • Wave?? Or Small Particles?? • Properties: Wave like character • λ = wavelength γ = frequency • Energy E = hγ • h=Planck constant (6.6256 x 10-27 erg/sec) • γ= C/λ C= speed of light • E = h C/λ

8. What is Matter?

9. Both chemical structures and the arrangement of the molecules affect the way in which any given material interacts with energy.

10. How does radiant energy interact with matter? A given molecule can absorb only radiation of a certain definite frequency. Red, blue and yellow light not just a single wavelength or frequency. Given molecule can exist only in certain well-defined energy state.

11. Energy levels are not continuous. • Quantized? The energy difference between two defined energy levels is fixed. • The molecules or atoms of same chemical species absorbsame frequency. • The molecules or atoms of different chemical species absorbdifferent frequency • The uniqueness of the frequencies at which a given molecular species absorbs is the basis of absorption spectroscopy.

12. The Absorption of Energy by Atoms

13. The Absorption of Energy by Molecules

15. Vibration of Molecules

16. Absorption Caused by Electronic Transistors in Molecules • The vibrational and rotational energies of the molecules are added to the electronic energies. • The difference in vibrational or rotational energy leads to the absorption of energy over widefrequency range.

17. The Effect of the Absorption of Energy

18. The Emission of Radiant Energy by Atoms and Molecules

19. In the case of molecules • Not all molecules fluorescence, and very few phosphorescence. • Fluorescence intensity is very high. • Can detect very small conc. of certain compound

20. Methods of Excitation of Atoms • 1-Electronic Discharge • Putting the sample in an electric discharge between two electrodes. • The sample breaks down into excited atoms • All different atoms emit their emission spectrum.

21. 2-Flame Excitation • This is the basis of flame photometry. • Flame energy is lower than that of an electrical discharge • Fewer transitions are possible-Fewer spectrum lines.

22. 3-Excitation by Radiation • Sample absorb uv and reemit fluorescence. • This the bases of Molecular Fluorescence (RF). • Phosphorescence: • If the e changes its direction of spin before returning to the G.S. emission will be difficult (forbidden). • The radiation takes place over a long period of time.

23. Absorption Laws

24. 1-Lambert׳s Law • A = a b • A = absorbance • a = absorptivity of the liquid • b = optical path length • a b = log I0/I1 • I1 = I0 10 -ab • I0 = I1 10 ab • Relationship between absorbance and optical path length

25. 2- Beer΄s Law • A = a c • c = concentration of solution. • a c = log I0/I1 • I1 = I0 10 -ac • I0 = I1 10 ac • Relationship between the absorbance and the concentration of the solution

26. 3-Beer-Lambert Law • A = a b c • I0 = I1 10 abc • Linear relationship between A and c if b is constant and the radiation wavelength constant. • By measuring I1/I0 we can measure A, and we can calculate c. • Valid for low conc. But deviations are common at higher concentrations.

27. 4-Deviation from Beer׳s Law • 1-Impurities. • 2-Chemical equilibrium. • 3-Optical slit. • 4-Dimerization. • 5- Interaction with solvent • Calibration curve will eliminate all the deviations.

28. Calibration Curves • Series of solutions with known concentration. • When a, b, I0 are constant • c ά –logI1 • Base line disturbed by an interfering compounds. • Can solve this problem : • 1-Mathmatically • 2-Double beam instrument (reference cell)

29. 2-Standard Addition Method • This method used if: • 1-No suitable calibration curve. • 2-Time delay. • 3-No sufficient information on the solvent in the sample. • 4-Very low concentration. • Known conc. are added to the sample

30. Chapter 2Concepts of Spectroscopy It is important to know 1- The wavelength at which the sample emits or absorbs radiation. 2- The intensity of radiation or the degree of absorption. The basic design of all instruments: 1- Source of radiation (absorption) or excitation (emission). 2- Monochromatic (selecting the wavelength). 3- Sample holder. 4- Detector (measure the intensity of radiation).

31. 1- single beam optics:

32. a- Radiation Source • 1-Emite radiation of wavelength in the range to be studied (x-ray, infrared, ultraviolet). • 2-The Intensity in all range should be high. • 3-The intensity should not vary significantly at different wavelengths. • 4-The intensity should not fluctuate over long time intervals.

33. b-Monochromator • Function: disperse the radiation according to the wavelength. • 1-Prism Monochromators: • The prism bendslonger-wavelengths (red end) radiation less than it does shorter-wavelength radiation (blue end)?. • The refractive index of prism is greater for short-wavelength light than it is for long-wavelength light.

34. 2-Grating Monochromator: • More popular than prism. • A series of parallel lines cut into a plane surface. • From 15000-30000 groves per square inch. • The more lines per square inch, the shorter λ of radiation that the grating can disperse and the greater the dispersing power. • Separation of light occurs because light of different λ is dispersed at different angles.

35. 3-Resolution of a Monochromator • The ability to disperse radiation is called resolving power (dispersive power). • The resolving power of a prismincrease with the thickness of the prism. • The resolving power of a prism increase when the material used is improved. • The resolving power of a gratingincrease with increase the line groves.

36. c-Slits • Used to select the light beam after it has been dispersed by the monochromator. • The entrance slit selects a beam of light from the source. • The exit slit allow radiation from the monochromator to proceed to the sample and detector. • Only a selected λ range is permitted through the slit. • Other radiation is blocked and prevented from passing further. • The slits are kept as narrow as possible to ensure optimum resolution.

37. d-Detector • Measure the intensity of the radiation that falls on it. • Radiation energy is turned into electrical energy. • The amount of energy produced usually low and must be amplified. • Amplifying the signal from the detector increase its sensitivity. • If the signal is amplified too much, it becomes erratic and unsteady (noisy).

38. e- Uses for Single-Beam Optics • Single-beam optics are used for all spectroscopic emission methods. • The method allows the emission intensity and wavelength to be measured accurately and rapidly. • In spectroscopic absorption studies the intensity before and after passing the sample must be measured. • Any variation in the intensity lead to analytical error. (that is why double beam developed)

39. 2-The Double-Beam System. • Used for spectroscopic absorption studies. • One very important difference from single beam: • The radiation from the source is split into two beams with equal intensity (reference beam and sample beam). • Any variation in the intensity of source I0 simultaneously decreases I1 but does not change the ratio I1/I0.

40. Chapter 3Infrared Absorption. • The wavelength (λ) of infrared (ir) radiation falls in the range 750 nm- 4500 nm. • The frequency (u) range: 2.2x1014-7.5x1015 cps. • Infrared radiation has less energy than visible radiation but more than radio waves.

41. A-Requirements for Infrared Absorption • 1-Correct Wavelength of Radiation: • Molecules absorb radiation when some part of the molecule (atom, or group) vibrates at the same frequency as the incident radiant energy. • After absorbing radiation, the molecule vibrate at an increased rate. • Atoms can vibrate in several ways. • The rate of vibration is quantized and can take place only at well defined frequencies that are characteristic of the atom.

42. 2-Electric Dipole • For a molecule to be able to absorb ir, it must have a changeable electric dipole. • The dipole must change as a result of the vibrational transition resulting from ir absorption. • If the rate of change of the dipole during vibration is fast, the absorption of radiation is intense (and vice versa). Electric dipole: a slight positive and a slight negative electric charge on the atoms

43. B-Movements of Molecules: • The total radiant energy absorbed by molecules = (the molecule's vibrational energy + the molecule's rotational energy) • Rotational energy levels are very small compared to vibrational energy levels.

44. 1- Vibrational Movement • u : frequency of vibration • K : constant. • f : binding strength of the spring • m : reduced mass.

45. Modes of vibration of C and H in methane molecule including: • a-symmetrical stretching. • b- asymmetrical stretching. • c- scissoring. • d- rocking. • e- wagging. • f- twisting. • Each of the modes vibration absorb radiation at different wavelength.

46. 2- Rotational Movement • At the same time that the parts of a molecule vibrate toward each other, the molecule as a whole may rotate (spin). • The energy involved in spinning a molecule is very small compared to the energy required to cause it to vibrate.

47. C-Equipment (double beam system) • 1- Radiation Source: Both sources fulfill important requirements: 1-steady intensity. 2-intensity constant over long periods of time. 3-wide wavelength range. But the intensity of the radiation from them is not the same at all frequencies.

48. 2- Monochromators • Select desired frequency from source, and eliminate the radiation at other frequencies. • a- Prism Monochromator: • Material must be: • 1- Transparent to IR radiation (not glass, not quartz). • 2-Smooth (prevent random scattering). • 3-High quality crystal. • 4-Dry all time (use heater to keep dry). • 5-The machine must be in air condition room. • Material used can be single large crystal metal salt : NaCl, (KBr,CsBr), or CaF2.

49. B-Grating Monochromators: • Recently it is more popular in IR spectroscopy. • Material : Aluminum. • Advantages of grating: • 1- Stable in the atmosphere and are not attacked by moisture. • 2- Can be used over considerable wavelength range.

50. 3- Slit Systems: Allow small section of radiation beam to pass through exit slit to the detector. 4- Detectors: