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Atoms or molecules that are excited to high energy levels can decay to lower levels by emitting radiation (emission or luminescence). For atoms excited by a high-temperature energy source this light emission is commonly called atomic or optical emission (atomic-emission spectroscopy,) and for atoms excited with light it is called atomic fluorescence (atomic-fluorescence spectroscopy.)
Atomic-emission spectroscopy (AES) uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration. Analyte atoms in solution are aspirated into the excitation region where they are desolvated, vaporized and atomized by a flame, discharge, or plasma. These high-temperature atomization sources provide sufficient energy to promote the atoms into high energy levels. The atoms decay back to lower levels by emitting light.
AES employing a flame, also called flame emission spectroscopy (FES) or flame photometry, has found widespread application in elemental analysis. It can be used for both quantitative and qualitative analysis and it is a single element method. Its most important uses are in the determination of sodium, potassium, lithium and calcium in biological fluids and tissues.
The sample must be converted to free atoms, usually in a high-temperature excitation source e.g., a flame. Liquid samples are nebulized and carried into the flame by a flowing gas. The excitation source must desolvate, atomize and excite the analyte atoms. The flame supplies the sufficient energy to promote the atoms into high energy levels.
As the atoms decay to their ground stage, the emitted radiation passes through the monochromator that isolates the specific wavelength for desired analysis. A photodetector measures the radiant power of the selected radiation.