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ATOMIC ABSORPTION SPECTROSCOPY

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Jinnah University For Women

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ATOMIC ABSORPTION SPECTROSCOPY

  1. 1. BUSHRA IQBAL(11740)
  2. 2. HISTORY The beautiful phenomenon of “RAINBOW” was the first dispersed spectrum. In 1665 NEWTON took the first and the most important step towards the development of spectroscopy. In 1859 G.R KIRCHOFF and R BUNSEN emerged as the FATHER OF MODERN SPECTROSCOPY.
  3. 3. SPECTROSCOPY The study of structure of atom or molecules. Used in analysis of wide range of sample Can classify in atomic or molecular spectroscopy.
  4. 4. ATOMIC SPETROCOPY MOLECULAR SPECTROSCOPY
  5. 5. ABSORPTION SPECTROSCOPY • It gives the measurement of absorbed energy by the atom or molecule after which it excite and gives the absorbed energy in the form of absorption spectrum
  6. 6. ATOMIC ABSORPTION SPECTROSCOPY • Atomic absorption spectroscopy is a technique for determining the concentration of a particular metal element in a sample. Atomic absorption spectroscopy can be used to analyze the concentration of over 62 different metals in a solution.
  7. 7. TYPES OF ATOMIC SPECTRA 1) ATOMIC EMISSION SPECTRA:
  8. 8. 2) ATOMIC ABSORPTION SPECTRA:
  9. 9. 3) ATOMIC FLUORESCENCE SPECTRA
  10. 10. COMPARISON ATOMIC EMISSION ATOMIC ABSORPTION SPECTROSCOPY SPECTROSCPY • Examines the wavelengths of • Measures the loss of photons emitted by atoms or electromagnetic energy after it molecules during their transition illuminates the sample under from an excited state to a lower study. energy state. • The energy in certain amount • Each element emits a is absorbed during transition characteristic set of discrete to the higher level. wavelengths. • The amount of energy • By observing these wavelengths absorbed gives estimate of the the elemental composition of concentration of the analyte in the sample can be determined. the sample.
  11. 11. PRESENTORS: RIMSHA ISMAIL (11780) RUTABA MURTAZA (11782)
  12. 12. THEORY OF ATOMIC ABSORPTION SPECTROSCOPY • Absorption therefore is carried out by unexcited atoms.
  13. 13. CONCEPT OF ATOMIC ABSORPTION SPECTROSCOPY • In 1955, A. WALSH and another one of C T J ALKAMADE and J M W MILATZ.
  14. 14. PRINCIPLE OF ATOMIC ABSORPTION SPECTROSCOPY EVAPORATION VAPORIZATION SOURCE SOLUTION MIST DISSOCIATION GAS SOLID hv THERMAL FLAME EXCITATION EMISSION hv2 RE-EMISSION ABSORPTION OF RADIANTENERG (FLUORESCENCE) Y RECORDER DETCETOR MONOCHROM AMPLIFIER ATER
  15. 15. • The total amount of light absorbed may be given mathematically by the following expressions: Total number of light absorbed = πe2/mc Nf Where, e= is the charge on the electron of mass m= mass of electron c= is the speed of light N= is the total number of atoms that can absorb at frequency in the light path v= frequency f= is the oscillator strength or ability of each atom to absorb at frequency π= is constant The above equation can be written as: Total amount of light absorbed= Constant x N x f
  16. 16. INSTRUMENTATION OF ATOMIC ABSORPTION SPECTROSCOPY
  17. 17. 1. RADIATION SOURCE The main sources used for atomic absorption are: I. Hollow Cathode Lamp (HCL) II. Electrode less Discharge Lamp (EDL)
  18. 18. I. HOLLOW CATHODE LAMP
  19. 19. II. ELECTRODELESS DISCHARGE LAMP
  20. 20. SOURCE MODULATION
  21. 21. 2. ATOMIZERS There are two types of atomizers which are used in Atomic Absorption Spectroscopy. • Flame Atomizers • Electrothermal Atomizers
  22. 22. FLAME ATOMIZER: • Flame is used to atomize the sample • Sample when heated is broken into its atoms PRINCIPLE: • High temperature of flame causes excitation • Electrons of the atomized sample are promoted to higher orbitals, by absorbing certain amount of energy QUANTITATIVE ANALYSIS: • The amount of energy absorbed is specific for a particular element (for electronic transition). • Amount of absorbed radiation is a quantitative measure for the concentration of the element to be analyzed
  23. 23. SAMPLE NEBULIZER ASSEMBLY FLAME (ATOMIZATION OCCURS) CONVERSION INTO FINE MIST AEROSOL & SMALL MIXES WITH DROPLETS OF COMBUSTION SOLUTION GASES ASPIRATED INTO SPRAY CHAMBER (MIXING CHAMBER)
  24. 24. Sample to be Nebulizer: nebulized is sample+fuel+ taken (aspirated) oxidant via a capillary fine mist or tube aerosol
  25. 25. Natural Gas Air 1700-1900 39-43 Natural Gas Oxygen 2700-2800 370-390 Hydrogen Air 2000-2100 300-440 Hydrogen Oxygen 2550-2700 900-1400 Acetylene Air 2100-2400 158-266 Acetylene Oxygen 3050-3150 1100-2480 Acetylene Nitrous Oxide 2600-2800 285
  26. 26. - Wavelength selectors - Produces monochromatic light Consists of: 1) Entrance slit 2) Diffraction grating 3) Exit slit Diffraction gratings are mostly used rather than prisms
  27. 27. Electro thermal atomization (ETA) (also known as Graphite furnace atomization) Used for improvement and betterment in the limit- of-detection and sensitivity for atomic absorption measurements.
  28. 28. GRAPHITE FURNACE ATOMIZERS:
  29. 29. Graphite tube Enclosed water cooled housing Transparent windows Inert purge gas control Electrical contact
  30. 30. 1.Drying Atomization 2. Ashing or of sample pyrolysis 3.Atomization
  31. 31. WORKING OF PHOTOMULTIPLIER TUBE
  32. 32. V ideo0003.3gp
  33. 33. The signal could be displayed for readout in the readout devices. Readout devices: • Digital voltmeter • Simple galvanometer • Potentiometer • Computer
  34. 34. • Atomic Absorption spectrophotometric measurements are done extensively by using;  Single-Beam AA Spectrophotometer  Double-Beam AA Spectrophotometer
  35. 35. • The first AAS was presented by Walsh and co-workers in Melbourne in 1954, was a double beam atomic absorption spectrophotometer. • Walsh worked with Perkin-Elmer, the first AAS instrument developed by that company was MODEL 303.
  36. 36. Single Beam AA Spectrophotometer: Single beam measurements are depended upon the varying intensity of a single beam of light having a single optical path. That is why called as single beam AA spectrophotometer.
  37. 37. Double Beam AA Spectrophotometer: • It split the light from the source into a ‘sample beam’ (focused to the sample cell) and a ‘reference beam’ (focused around the sample cell). • Such an instrument is called as double beam AA spectrophotometer, as measurements are made on varying intensity of double beams of light in dual optical path.
  38. 38. Single Beam Instruments Double Beam Instruments  Simple, Less expensive, less complexity  Complex, more expensive, not easily made  Low automation, more efficiency of light  High speed automation, less light efficiency  More time consuming  Less time consuming  Low stability  Increased stability  Depend upon single beam intensity  Depend upon ratio between both beams  More chances of fluctuations  Lesser fluctuations in readings Sample and Reference placed separately  Sample and Reference are kept at same time High light throughput, more resolution  Less light throughput, decreased resolution More warm-up time is required Less or reduced warm-up time required
  39. 39. SAMPLE PREPARATION • The preparation of the sample solution for a solid material is most time consuming step of process of analysis in an atomic absorption spectroscopy. It involves following steps; Weighing of sample Dissolution in appropriate solvent or digestion using different techniques Dilution of sample if necessary
  40. 40. • A sample employed for atomic absorption spectroscopy in the laboratory is placed into one of the following categories: • Considerations are to be given to some of the general principles involved in the various sample preparations.
  41. 41. • A little preparation is required with this sort of sample. • These include samples in raw and treated water, sea waters, biological fluids, beer, plating solutions, effluents, wines etc.
  42. 42. • It include petroleum products, many of which can be directly be aspired. Examples of such solvents used are m- heptene, aliphatic ketones, (e.g. methyl iso butyl ketone) aliphatic esters, alcohols and xylene, cyclohexanes, isopropanol etc. are frequently employed. • Note: When samples are analyzed in organic solvents some adjustments such as ‘BURNER CONTROLS’, proper ventilation or other appropriate settings must be used.
  43. 43. • These include solid samples of fertilizers, ceramics, alloys or rocks. • These are solvated by using appropriate aqueous or acid medium depending on solubility. Such as hot water, concentrated acids, acidic mixtures, dilute acids etc. • Other techniques can also be employed such as fusion prolonged acid digestion, wet ashing etc to yield sample solutions.
  44. 44. • These includes typically material of foods, leaves, tissue, biological solids, polymers, plants, feedstuff etc. • Before solublization of such samples, there is a requirement of destruction via wet digestion or ashing in a furnace (muffle).
  45. 45. • Atomic absorption analytical works or procedures can be employed in analyzing gases indirectly as liquid sample. PREPARATION: Separate metals Using Millipore Wash or from gas filter disc dissolve Analyze using Using nitric acid standards
  46. 46. Techniques Used For Certain Sample Preparations: • As discussed in previous topics, some solid sample requires special techniques for dissolution. Such sample preparation requires time and proper handling. Wet Ashing Or Wet Digestion: Undissolved in Inorganic samples Treated with acids aqueous solvents Clean liquid with no Such as Perchloric Digestion of single element acid, HCl, HNO3, complexes, silicates being removed
  47. 47. Dry Ashing: Heated in Mix left Remove inorganic Weighed furnace over in particles like lead sample or mercury (muffle) acid Microwave Dissolution: (type of digestion)
  48. 48. Extraction and Concentration process: • Such an operation is done if sample contain species interfering in absorption or the concentration of sample desired is in low concentration to show absorption readings. Such a process involves,
  49. 49. • The viscosity adjustment can be done with suitable solvents which can be that in a way solvent should; o Dissolve or mix completely with the sample o Well burnt but in a controlled manner o Be in pure state such that possessing no species having molecular absorption in region o Not yield harmful by-products o Not be expensive
  50. 50. PRESENTOR: Shumaila Eliyas
  51. 51. “Increase or decrease in the size of the signal obtained from the analyte as a result of the presence of some other known or unknown component in the sample” Types of interference:  Spectral interference Chemical interference
  52. 52. Spectral interference This may be caused by direct overlap of the analytical line with the absorption line of the matrix element. HOW TO OVERCOME ? By choosing an alternate analytical wavelength By removing the interfering element from the sample.
  53. 53. Examples of spectral interferences
  54. 54. Chemical interference Formation of compound of low volatility Decrease in calcium absorbance is observed with increasing concentration of sulfate or phosphate
  55. 55.  By increasing flame temperature Use of releasing agents (La 3+ ) Cations react with the interferent releasing the analyte Use of protective agents: They form stable but volatile compounds with analyte.
  56. 56. Ionization interference Ionization of ground state gaseous atom with in a flame will reduce extent of absorption in AAS. M ↔ M+ + e HOW TO MINIMIZE:  Low temperature of the flame  Addition of an excess of ionization suppressant e.g. the alkali metals (K, Na, Rb, and Cs)
  57. 57. Influence of potassium on the ionization of barium
  58. 58. ATOMIC ABSORPTION SPECTROSCOPY
  59. 59.  Pharmaceutical  Biological  Biochemical For detection of purity and consistency of these trace metals Also for quantitative determination of metals mainly in solid sample as mineral, ores and alloys
  60. 60. • Magnesium in cast iron • Silver, Zinc, Copper and Lead in Cadmium metal • Method of multiple standard addition • A plot of absorbance against the amount of standard can be used to determine the amount of copper in a sample.
  61. 61.  Determination of trace metal in a silicon foam cavity wound dressing  Zinc in Zinc insulin suspension and tetracosactrin Zinc injection  Copper and Iron in ascorbic acid  Aluminum in albumin solution and Ca, Mg, Mercury  Zinc in water used for diluting haemodialysis solution
  62. 62. •For the analysis of pharmaceutically or therapeutically essential component of formulation, such as Zinc in Zinc- insulin, minerals in multivitamin-mineral preparation and Ca, Mg, Al in antacids. •To establish concentration limits where the metal is regarded as an impurity.
  63. 63. •Mining industries •Petroleum industries •Determination of metallic elements in food industry like Copper, Zinc and Nickel in vegetable oil and copper in beer.

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