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Atomic absorption spectroscopy

Atomic absorption spectroscopy
Atomic falme absorption spectroscopy

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Atomic absorption spectroscopy

  3. 3. INTRODUCTION Atomic absorption spectroscopy (AAS) is a spectro analytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation. In analytical chemistry the technique is used for determining the concentration of a particular element in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution or directly in solid samples used in that.
  4. 4. Atomic absorption spectrometry has many uses in different areas of chemistry such as clinical analysis of metals in biological fluids and tissues such as whole blood, plasma, urine, saliva, brain tissue, liver, muscle tissue, semen, in some pharmaceutical manufacturing processes, minute quantities of a catalyst that remain in the final drug product, and analyzing water for its metal content.
  5. 5. PRINCIPLE The intensity of the light absorbed by the neutral atoms is directly proportional to the concentration of the element and obey the Beer’s law over wide concentration range. The intensity of the radiation absorbed by the neutral atoms is measured using photometric detector.
  6. 6. COMPONENTS OF AAS 1) Light source 2) Burner 3) Chopper 4) Monochromator 5) Detector 6) Readout device
  7. 7. LIGHTSOURCE The source of the light in AAS is Hallow Cathode Lamp(HCL). The cathode lamp is made up of specific / alloys of elements or coating of elements on cathode. When the current is applied between anode and cathode, metal atoms emerge from hollow cup and collides with filler gas, which is argon or neon. Due to these collisions, number of metal atoms are excited and emit their characteristic radiation. This characteristic radiation is absorbed by the neutral atoms of the same element in ground state which occur in the flame, when the sample sprayed.
  8. 8. It is not possible to use a source of light with a Monochromator because this arrangement gives a radiation with a band with of 1nm, where as the hollow cathode lamp gives a band width of 0.001 to 0.01nm which is highly desirable to achieve specificity
  9. 9. BURNER BURNERS Flame absorption technique Graphite furnace technique Hydride system technique The temperature of the flame is not critical but atomization of sample solution, like in flame photometry is required. Burners with fuel and oxidant as specified in flame photometry are used. In this air acetylene, nitrogen are use for specific metal elements.
  10. 10. FLAMEBURNER Air-acetylene is the preferred flame for the determination of approximately 35 elements by atomic absorption. The temperature of the air-acetylene flame is about 2300 °C. An air-acetylene flame can be used Perkin-Elmer burner heads. Length of the burner is 10cm. Air-acetylene is the preferred flame for the determination of approximately 35 elements by atomic absorption. The temperature of the air-acetylene flame is about 2300 °C. An air-acetylene flame can be used with all Perkin-Elmer burner heads. The step-by-step procedure is given for the operation of the acetylene/air flame. air-acetylene flame, the acetylene flow is about 4 liters/minute
  11. 11. The nitrous oxide-acetylene flame has a maximum temperature of about 2900 °C and is used for the determination of elements which form refractory oxides. It is also used to overcome chemical interferences that may be present in flames of lower temperature. For the nitrous oxide-acetylene flame, the acetylene flow is about 14 liters per minute or 30 cubic feet per hour.
  12. 12. The graphite tube is just visible between the two electrodes in the centre of the image. The electrodes are usually water- cooled, while an inert gas is used to exclude air from the furnace tube in order to prevent sample oxidation. The close- up shows the view through one end of the electrode/furnace assembly. Note the power lines and cooling water connections on the back GRAPHITEFURNANCE Graphite Furnace(GF) is also known as Electro thermal is used in the type of spectrometry that uses a graphite-coated furnace to vaporize the sample. Length of the GF is 5cm
  13. 13. HYDRIDESYSTEM TECHNIQUE It is applied namely for determination of trace amounts of As, Se (Te, Sb, Ge, Sn, Pb...) . The gaseous hydride of the analyte (e.g. AsH3 or H2Se) is formed from the corresponding compound of the analyte (H3AsO3 or H2SeO3) by reducing reaction with NaBH4 (“sodium borohydride”); the reaction takes place in a hydride generator, gaseous products are delivered to the atomizer (usually a heated quartz tube). The technique is by 2-3 orders of magnitude more sensitive than Flame AAS. As a consequence of analyte transfer into gaseous phase most of interferences are eliminated (namely those manifested on analytical lines of As and Se that are located in the region of wavelength <200 nm).
  15. 15. CHOPPER Which is used to measured to use the intensity of the light absorbed by elements without interference by the radiation from the flame it self. Its not practical to have two separate cells, so the light is simply split, simply split, with half being sent around the atomization with half being sent around the atomization source. source. This reduces some noise from This reduces some noise from the atomization the atomization source and accounts for instrumental variations. accounts for instrumental variations.
  16. 16. MONOCHROMATORS For Good Resolution Of 1nm or Less Than 1nm Required
  17. 17. The intensity of radiation absorbed by the elements in the UV / visible region (190-900nm) can be detector using Photo Multiple Tube(PMT). DECTECTOR
  18. 18. READOUT DEVICE The readout device is capable of displaying the absorbing spectrum as well the absorbance at the specified wavelength. Beer’s law is over a wide concentration range. Example : galvanometer(ANALOG), computer(DIGITAL).
  19. 19. APPLICATION OF AAS AAS is mainly use for quantitative analysis of various elements presents in different samples(identification). 1) Estimation of trace elements in biological fluids(Blood, Urine, Plasma, etc.) 2) Estimation of metals like Cu, Ni, Zn in food samples. 3) Estimation of Mg, Zn, etc in blood. 4) Estimation of Zn in insulin injection. 5) Estimation of Thiomersal compounds(OrganoMercury compound) 6) Estimation of elements in soil, water, ceramic, effluents, etc
  20. 20. DIFFERENT BETWEEN AAS and FP PARAMETER / CHARACTERISTIC FLAME PHOTOMETRY ATOMIC ABSORPTION SPECTROSCOPY Concentration of elements Radiation emitted by exited atoms Radiation absorbed by ground state atoms Temperature Exited atoms obtained by thermal energy of flame The thermal energy of flame is just enough to get neutral atoms
  21. 21. Linearity (concentration Vs parameters measured) Near linear over a narrow range of concentration Its obey the Beer’s law. Its linear over wide range of concentration The number of elements that can be analyzed by the technique Very few elements analyzed especially group IA & IIA Wide range of elements are analyzed