Atomic Absorption Spectroscopy: Radiation and Light Sources

For AAS to obey the Beer–Lambert law, the radiation source should emit an even narrower range of wavelengths than the analyte atom absorbs.

The two common narrow-range 'line' sources are hollow-cathode lamps, or HCLs and electrodeless-discharge lamps, or EDLs.

An HCL has a cylindrical hollow cathode coated with the element being analyzed and a tungsten or zirconium anode, all enclosed in a glass tube filled with an inert gas at low pressure.

Applying a voltage across the electrodes ionizes the inert gas atoms, which energetically bombard the cathode coating, knocking out—or 'sputtering'—some atoms.

Further collision excites some sputtered atoms, which transition back by emitting radiation of the characteristic wavelength.

Some elements need the more intense and precise EDL line source—a sealed quartz tube filled with an inert gas and the analyte element or its salt.

An intense field of radio-frequency or microwave radiation inside the tube vaporizes the atoms and excites them, causing the emission of their characteristic spectrum.