1) Atomic absorption spectroscopy (AAS) was introduced in 1955 by Alan Walsh as a technique to determine the concentration of metals in liquid samples. 2) AAS works by vaporizing the metallic species from a liquid sample into a flame, where some metal atoms absorb light at specific resonant wavelengths that are characteristic of each metal. 3) The amount of light absorbed at the resonant wavelength is directly proportional to the number of ground state metal atoms in the flame and can be used to determine the concentration of the metal in the original sample.