What is Atomic Spectroscopy?
Atomic spectroscopy is actually not one technique but three: atomic absorption, atomic emission, and atomic fluorescence. Of these, atomic absorption (AA) and atomic emission are the most widely used.

What is Atomic Absorption ?
Atomic absorption is the process that occurs when a ground state atom absorbs energy in the form of light of a specific wavelength and is elevated to an excited state. The amount of light energy absorbed at this wavelength will increase as the number of atoms of the selected element in the light path increases. The relationship between the amount of light absorbed and the concentration of analyte present in known standards can be used to determine unknown concentrations by measuring the amount of light they absorb. Instrument readouts can be calibrated to display concentrations directly.

The basic layout of an atomic absorption system is shown here

The light source is usually a hollow cathode lamp (HCL) which emits radiation at resonance wavelength of the analyte element and is of a very narrow bandwidth (0.001nm). Since the cathode is constructed of the analyte element (or an alloy of it) the radiation will be specific to that element only. The oxidant gas (air of nitrous oxide) flows into the nebuliser and creates a partial vacuum which causes the solution containing the analyte element to be aspirated into the nebuliser, via a plastic capillary tube, and is then converted into an aerosol. The oxidant/aerosol is then swept into the spray chamber where mixing with the fuel gas occurs. The mixture is then forced into the flame which is of a sufficiently high temperature to cause the atomisation of the analyte element. The free atoms thus formed absorb radiation from the HCL which is focused onto the centre of the flame and about 5-10mm above the burner slot. This radiation which has now been attenuated by an amount related to the concentration of free atoms in the flame (and hence in the solution) now enters the monochromator. This allows only a narrow region of the spectrum, typically 0.5nm centred on the pre selected wavelength of the resonance line of the analyte element to pass into photomultiplier. This amplifies the resulting display. This output can also be processed by a data handling system, typically a PC.