Module 19: Atomic Absorption, Fluorescence, X-ray Spctromtry

• What is AAS commonly used for?


  To measure concentration of trace metals that are not easily excited.
• What is one advantage of AAS over flame emission?


  AAS is generally more sensitive than flame emission.
• What are some applications of AAS?


  Detecting toxic elements in food products and lead determination in petrol.
• What is a disadvantage of AAS?


  Samples must be in solution or at least volatile.
• How does AAS measure concentration?


  By detecting absorption of electromagnetic radiation by atoms.
• What interferences can affect AAS?


  Chemical, matrix, and ionization interferences.
• What is the role of the monochromator in AAS instrumentation?


  To isolate the desired emission line from other lamp emission lines.
• What is the function of the PM tube in AAS?


  It serves as the light detector in the AAS system.
• Why is the lamp output modulated in AAS?


  To avoid interference from emission by excited atoms in the flame.
• What are the two forms of flameless atomizers mentioned?


  Graphite tube and carbon rod.
• What is the advantage of flameless vaporization?


  It eliminates anomalous results and increases sensitivity.
• How is the extent of radiation absorption related to atomic vapor?


  It is related to the length of the path traversed and the concentration of absorbing atoms.
• What is the purpose of the hollow cathode lamp in AAS?


  It serves as the light source for atomic absorption spectrometry.
• What happens when the gas in the hollow cathode lamp is ionized?


  Excited ions collide with the metal coating, knocking off atoms and emitting characteristic light energy.
• What is the principle behind the flame method in AAS?


  Vaporized metal atoms from the sample are found in the flame, which acts as the atomizer.
• How is quantitative measurement achieved in AAS?


  By preparing standard solutions and matching them closely in composition to the samples.
• What are the types of interferences in AAS?


  Spectral, chemical, and physical interferences.
• What is atomic fluorescence spectrometry (AFS)?


  It is an analytical method used to determine the concentration of elements in samples.
• What is a disadvantage of atomic fluorescence spectrometry?


  It is a single-element method and sensitive to environmental changes.
• How do electrodeless discharge tubes work?


  They are energized by an intense field of radio-frequency microwave radiation to excite analyte metal atoms.
• When was the first commercial Atomic Absorption spectrometer introduced?


  In 1959.
• What is the role of the deuterium continuum radiation source in AAS?


  It is used for background correction.
• What are the main components of an Atomic Absorption Spectrometer?


  • Sharp-line radiation source (hollow-cathode lamp)
  • Solution nebulizer and burner or electrically heated furnace
  • Monochromator
  • Photomultiplier
  • Recording system
• What are the advantages and disadvantages of atomic fluorescence spectrometry?


  Advantages:

  • High sensitivity and selectivity for certain elements (e.g., Hg, Sb, As, Se, Te)

  
  

  Disadvantages:

  • Single-element method
  • Sensitive to environmental changes
  • Limited range of applications
• What are the advantages and disadvantages of flameless vaporization?


  Advantages:

  • Elimination of anomalous results
  • Increased sensitivity
  • Ability to handle very small samples

  
  

  Disadvantages:

  • Complexity of the system
  • Potential for incomplete vaporization
• What are the types of interferences in AAS and how can they be corrected?


  Types of interferences:

  • Spectral
  • Chemical
  • Physical

  
  

  Corrections:

  • Matrix matching of samples and standards
  • Use of a standard addition method
  • Pretreatment of the sample