Atomic Spectroscopy: Basic Principles and Instruments


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A short lecture about Atomic Spectroscopy: Flame Photometry, Atomic Absorption, and Atomic Emission with Coupled Plasma (FP, AA and ICP-AES). Presented at 28.03.2011, Faculty of Agriculture, Hebrew University of Jerusalem, by Vasiliy Rosen, M.Sc.

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Atomic Spectroscopy: Basic Principles and Instruments

  1. 1. Atomic Spectroscopy:<br />Basic Principles <br />And Instruments<br />Vasiliy V. Rosen, M.Sc., ZBM Analytical Laboratory<br /><br />2011<br />
  2. 2. Atomic Spectroscopy<br />Absorption Spectroscopy: <br />AAS <br />Emission Spectroscopy: <br />FES, ICP-AES(OES)<br />Mass Spectrometry<br />
  3. 3. Atomic Spectroscopy<br />Ion Emission<br />Atom Emission<br />E – energy difference between two levels;<br />h – Plank’s constant, 6.626068 × 10-34 m2kg/s;<br />c – speed of light,  299 792 458 m/s;<br />λ – wavelenght, nm<br />After Boss. C.B. and Freden K.J. Concepts, Instrumentation and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry. 1997<br />
  4. 4. Atomic Spectroscopy<br />Nebulizer converts the solution into a spray<br />Flame (or Plasma) causes the solvent to evaporate, leaving dry aerosol particles, then volatilizes the particles, producing atomic, molecular and ionic species<br />After Skoog D. Fundamentals of Analytical Chemistry, 2004, p. 844<br />
  5. 5. Flame Emission Spectroscopy (FES)<br /><ul><li>Propane-butane flame ( 2000 – 3000 º C);
  6. 6. Optical filter is used to monitor for the selected emission wavelength produced by the analyte;
  7. 7. Suitable for elements with low excitation energy (Na, K, Li, Rb and Ca).</li></li></ul><li>Flame Emission Spectroscopy (FES)<br />Optic Filter<br />Flame<br />Data Display<br />Nebulizer<br />Flame Photometer M-410 (Sherwood Scientific, UK)<br />
  8. 8. Atomic absorption spectroscopy (AAS)<br /><ul><li>Gases mixture flame (1800 – 4500 º C): air-propane, air-acetylene etc. ;
  9. 9. Atomic absorption spectrometry quantifies the absorption of ground state atoms in the gaseous state ;
  10. 10. The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels . The analyte concentration is determined from the amount of absorption.</li></li></ul><li>Atomic absorption spectroscopy (AAS)<br />Elements detectable by AA are highlighted in pink<br />
  11. 11. Atomic absorption spectroscopy (AAS)<br />Operation principle of AAS<br /><ul><li>Light source – hollow cathode lamp. Each element has its own unique lamp.
  12. 12. Atomic cell – flame (gas mixture) or graphite furnance (accepts solutions, slurries, or even solids).
  13. 13. Detector – photomultiplier.</li></ul>After G.Ma and G.W. Gonzales,<br />
  14. 14. Atomic absorption spectroscopy (AAS)<br />
  15. 15. Atomicemissionspectroscopy<br />ICP-AES<br />Inductively Coupled Plasma -<br />Atomic Emission Spectrometry<br />
  16. 16. ICP-AES<br />Basics<br /><ul><li>Atomic emission spectroscopy measures the intensity of light emitted by atoms or ions of the elements of interest at specific wavelengths;
  17. 17. Inductively Coupled Plasma spectrometers use emission spectroscopy to detect and quantify elements in a sample;
  18. 18. ICP-AES uses the argon plasma (6000-10000º C) for atomization and excitation of the sample atoms;
  19. 19. ICP-AES determines approximately all of the elements except gases and some non-metals (C, N, F, O, H). </li></li></ul><li>
  20. 20. ICP-aes spectrometer arcos<br />
  21. 21. Schematic diagram of the processes in the ICP<br />After SpectroGmbh, Germany<br />
  22. 22. ICP spectrometer<br />Main Systems<br /><ul><li>Sample Introduction System: to deliver the sample solution to the plasma. Consists of pump, nebulizer and spray chamber.
  23. 23. Plasma: to generate the signal. Plasma is forming in the torch from gas argon.
  24. 24. Optics: to measure the signal.
  25. 25. Computer with appropriate software: for controlling the instrument and measuring process.</li></li></ul><li>ICP-AES: Sample introduction system<br />Torch with Plasma<br />Nebulizer (cross-flow)<br />Spray Chamber<br />To Waste<br />Sample Solution Entrance<br />Argon Supply<br />
  26. 26. ICP-AES: Plasma<br />Inductively Coupled Plasma Source<br />A plasma is a hot, partially ionized<br />gas. It contains relatively high<br />concentrations of ions and electrons. <br />Argon ions, once formed in a plasma, are capable of absorbing sufficient power from an external source to maintain the temperature at a level at which further ionization sustains the plasma indefinitely. The plasma temperature is about 10 000 K.<br />After Manning T.J. and Grow W.P., 1997<br />
  27. 27. ICP-AES: Plasma<br />Inductively Coupled Plasma Source<br />
  28. 28. ICP-AES: Radial (SOP) and axial (EOP)<br />EOP: End-on-Plasma<br />SOP: Side-on-Plasma<br /><ul><li>more suitable for hard matrices (concentrated samples);
  29. 29. alkali metals (Na, K, Li) calibration is more linear;
  30. 30. less spectral interferences;
  31. 31. lower sensitivity (Limit-of-Detection is higher);
  32. 32. more suitable for light matrices;
  33. 33. alkali metals (Na, K, Li) calibration is less linear;
  34. 34. more spectral interferences;
  35. 35. higher sensitivity (Limit-of-Detection is lower);</li></li></ul><li>ICP-AES: Radial (SOP) and axial (EOP)<br />After SpectroGmbh, Germany<br />
  36. 36. ICP-AES: optics<br />After SpectroGmbh, Germany<br />
  37. 37. ICP-AES: Sample Preparation<br />Microwave-assisted Digestion<br />Hot Plate<br />Digestion Block<br />Most samples have to be prepared for analysis by ICP. Solid samples are solubilized. Organic matter is "mineralized" i.e. converted to inorganic compounds.<br />
  38. 38. ICP-AES: calibration curve<br />
  39. 39. ICP-AES: spectral interferences<br />Au (gold) peak on 242.795 nm<br />
  40. 40. ICP-AES: spectral interferences<br />Au (gold) peak on 242.795 nm is interfered by Mn 242.794 nm <br />Au (gold) peak on 267.595 nm is free from Mn interference!<br />
  41. 41. ICP-AES, FEs and AAS: application<br /><ul><li>Clinical Analysis: metals in biological fluids (blood, urine);
  42. 42. Environmental Analysis: trace metals and other elements in waters, soils, plants, composts and sludges;
  43. 43. Pharmaceuticals: traces of catalysts used; traces of poison metals (Cd, Pb etc);
  44. 44. Industry: trace metal analysis in raw materials; noble metals determination.
  45. 45. Forensic science: gunshot powder residue analysis, toxicological examination</li></ul> ( e.g., thallium (Tl) determination)<br />
  46. 46. references<br /><ul><li>Boss, C.B. and Freden, K.J. Concepts, Instrumentation and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry. 1997
  47. 47. Skoog, D. Fundamentals of Analytical Chemistry, 2004
  48. 48. Ma, G. and Gonzales, G.B. Flame Atomic Absorption Spectrometry.
  49. 49. Manning T.J. and Grow W.P. Inductively Coupled Plasma Atomic Emission Spectrometry. The Chemical Educator, v.1. N 2. 1997.
  50. 50. Lecture by Dr. MordechayShoenfeld, “ICP-AES”, Course 71106, Faculty of Agriculture, HUJI. 2010.</li>