Atomic Absorption Spectroscopy

Atomic Absorption Spectroscopy (AAS)

• Measured A value greater than 0.1-0.2 has an RSD of 0.3-1% for flame and 1-5% for Electrothermal Atomization (ETA)
• ETA has better accuracy than flame due to higher efficiency of atomization

Flame vs Electrothermal Atomizer

• Flame: only 5% of the sample volume is atomized, with high volume of combustion gases as diluent
• ETA: high volume of sample available for atomization, resulting in better detection limits

Sample Introduction

• Criteria for sample introduction: reproducible measurement, high efficiency in atomization, no spectral or chemical interferences
• Sample introduction accessories: nebulizer, hydride generation, electrothermal vaporizer
• Hydride generation: used for determining As, Se, and Hg, especially at trace levels (300 times better than nebulizer-flame AAS)

Interferences

• Chemical interferences: more common than spectral interferences
• Types of chemical interferences:
  • Formation of low volatility compounds
  • Dissociation equilibria
  • Ionization equilibria

Formation of Low Volatility Compounds

• Analytes react with anions or cations to form low volatility compounds, reducing the population of ground state atomic vapor
• Examples:
  • Ca with SO42- and PO43-
  • Mg with Al

Minimizing Interferences

• Use higher flame temperature to volatilize products
• Add releasing agents (cations that react preferentially with the interferant)
• Examples:
  • Determination of Ca in a sample with PO43-
  • Determination of Mg in the presence of Al

Dissociation Equilibria

• In the atomizer, hot gaseous environment leads to dissociation and association reactions
• Dissociation of oxides and hydroxides leads to conversion of metallic constituents to elemental state
• "Rich" flames reduce MO and MOH to M, resulting in better signal

Standard Addition Method

• Used to remove background interference caused by flame emission effect

Source Modulation

• Light source is modulated to create an ac signal at the detector
• Discriminates between radiation from the hollow cathode lamp and radiation from excited atoms in the flame

Compare the accuracy and efficiency of atomic absorption spectroscopy methods, including flame and electrothermal atomization (ETA). Learn about the advantages of ETA and the factors affecting sample atomization.