Atomic absorption (AA) spectroscopy uses optical radiation and the absorption characteristics to detect single elements contained in a sample.  The technique is   based upon the absorption of energy at elementally unique wavelengths, providing specificity for multiple analytes. In AA, a sample is first atomized. This is traditionally done using flame or electrothermal atomizers. The atomized sample then is exposed to the optical light at the predetermined wavelength specific to the analyte of interest. The absorption is measured at each wavelength of interest using absorbance detectors.  The amount of energy absorbed by an analyte at a specific wavelength corresponds to the concentration of the element known to be excited by that wavelength according to the Beer-Lambert Law. While it may be used for general elemental analysis, this technique is common for analyzing metals in environmental, clinical, and pharmaceutical samples. AA instruments are typically benchtop models.  It is a mature technology and is available from multiple instrument manufacturers with various atomizers, light sources, and detector configurations.