14.6 : Atomic Absorption Spectroscopy: Atomization Methods

Atomic Absorption Spectroscopy (AAS) atomizes samples through flame atomization or electrothermal atomization. Flame atomization typically involves a nebulizer and spray chamber assembly to combine the sample with a fuel–oxidant mixture, creating a fine aerosol mist that enters a burner. Typically, the fuel and oxidant are combined in an approximately stoichiometric ratio. However, for atoms that are easily oxidized, a fuel-rich mixture may be more advantageous. Only about 5% of the aerosol droplets reach the flame, where they undergo desolvation in the primary combustion zone, leaving bare particles atomized in the inner flame. The gaseous atoms, ions, and molecular species quickly pass through the interzonal region for analysis before exiting the flame. Flame atomizers have low atomization efficiency due to large aerosol droplets not reaching the flame and significant sample dilution from combustion gases. However, the flame atomization efficiencies can be enhanced by continuously aspirating the sample, optimizing fuel-to-oxidant ratios, adjusting nebulizer flow rates, and setting the burner height.

Flame atomization is not suitable for samples with low analyte concentrations or limited volumes due to the small number of samples successfully atomized and detected. In contrast, electrothermal atomization, also known as graphite furnace atomization, uses a graphite tube to capture and concentrate the analytes and works well for small, discrete samples. In this technique, the sample is dried and charred before being atomized at high temperatures.

Elements such as As, Se, Sb, Bi, Ge, Sn, Te, and Pb can be atomized under milder conditions by chemically converting them into volatile hydrides before carrying them to the flame. Additionally, mercury determination can utilize a unique cold-vapor method due to its natural volatility.