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ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9

ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9. Absorption and fluorescence by atoms in a flame. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Atomization Flame Electrothermal (“furnace”). SAMPLE INTRODUCTION METHODS.

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ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9

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  1. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9

  2. Absorption and fluorescence by atoms in a flame.

  3. ATOMIC ABSORPTION AND ATOMIC FLUORESCENCE SPECTROMETRY Chap 9 Atomization Flame Electrothermal (“furnace”)

  4. SAMPLE INTRODUCTION METHODS Common Types of Atomizers (from SHN, 5e, Table 8-1) • Flame 1700 – 3100 °C • Electrothermal (“furnace”) 1200 – 3000 °C • Inductively coupled plasma (ICP) 4000 – 6000 °C • Electric arc 4000 – 5000 °C (e.g., Vreeland spectroscope)

  5. Table 9-1 Properties of Flames

  6. Regions in a Flame Fig. 9-2 (most useful)

  7. Temperature profiles for a natural gas - air flame Fig. 9-3

  8. Laminar Flow Burner Fig 9-5 source hv • Advantages: • quiet flame • long path length • (usually 10 cm) • superior • reproducibility • compared to all • other methods • Disadvantages: • poor efficiency • short residence time

  9. 2100 -2400 °C • Flame Atomization hν hν (acetylene) Laminar flow burner head Fig. 9-13 (a)

  10. hν in • Electrothermal Atomization (graphite furnace) Fig. 9-6 (a) • Advantages: • highly sensitive down • to pg of analyte • long residence time • more efficient than • flame • use with solid samples • Disadvantages: • poor reproducibility • small analytical range hν out

  11. The L’vov platform Fig. 9-6 (b)

  12. Graphite tube Graphite Furnace hv source detector

  13. Correct position for injecting sample into graphite furnace If injection is too high, sample splatters and precision is poor

  14. Heating profiles comparing analyte vaporization from walls and from platform (note constant T) not reliable reliable

  15. Atomic Absorption Instrumentation The Source

  16. Atomic Absorption Instrumentation Hollow-Cathode LampFig. 9-11 Ne or Ar at 1 – 5 torr Atoms sputter off cathode 300 V at 5 – 15 mA

  17. Typical output from an Fe HCL

  18. Atomic Absorption Instrumentation Electrodeless Discharge LampFig. 9-12 EDL • Higher intensity than HCL • Performance less reliable

  19. Typical Flame Spectrophotometer Fig. 9-13 (b) Double-beam

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