Atomic fluorescence spectroscopy (AFS) is an analytical technique that involves the electronic transitions of atoms in a flame, furnace, or plasma being excited by electromagnetic (EM) radiation. When these atoms absorb energy, they become excited and subsequently release energy as they return to their original state. This emitted light, or "fluorescence," is observed at a right angle to the incident beam. Both absorption and emission processes transpire at distinct wavelengths, which are characteristic of the specific atomic species present. AFS is particularly useful for determining mercury (Hg) and other elements that form volatile hydrides, such as arsenic (As) and selenium (Se).
The instrumentation required for atomic fluorescence measurements includes a high-intensity light source, an atomizer, a wavelength selector, and a detector. While a continuum source would be desirable, it is rarely used due to its low power output. Instead, pulsed hollow-cathode lamps, electrodeless-discharge lamps, xenon or mercury arc lamps, and lasers serve as potential light sources.
The fluorescence signal intensity is proportional to the target element's concentration and irradiation intensity, making high-intensity sources and minimal interfering radiation essential. Various chemicals, such as releasing and protective agents, can be introduced into the matrix to minimize chemical and spectral interferences that arise during atomization.
In atomic fluorescence spectroscopy, or AFS, atomized samples are irradiated by electromagnetic radiation to cause electronic transitions, and the emitted fluorescence radiation is measured.
The AFS instrument has a high-intensity light source, an atomizer, a wavelength selector, and a detector. Potential excitation sources include pulsed hollow-cathode lamps, electrodeless-discharge lamps, xenon or mercury arc lamps, and lasers.
Like in AAS, the analyte is atomized and then excited by the light source. The excited atoms release energy by fluorescence at wavelengths representing specific atomic species to return to their lower energy states.
Because atoms fluoresce at their optimal absorption wavelength, the source beam is at a right angle to the detector—usually a photomultiplier tube.
The fluorescence intensity is proportional to the target element's concentration. It is also proportional to irradiation intensity, making high-intensity sources and minimal interfering radiation essential.
Still, AFS is particularly effective for identifying volatile-hydride-forming elements and mercury.
Further, chemical and spectral interferences from atomization can be avoided by adding releasing or protective agents to the matrix.
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