Cold vapour atomic fluorescence spectroscopy

Cold vapour atomic fluorescence spectroscopy, sometimes referred to by the acronym CVAFS, is a subset of the analytical technique known as atomic fluorescence spectroscopy (AFS). Used in the measurement of trace amounts of volatile heavy metals such as mercury, cold vapour AFS makes use of the unique characteristic of mercury that allows vapor measurement at room temperature. Free mercury atoms in a carrier gas are excited by a collimated ultraviolet light source at 253.7 nm. The excited atoms re-radiate their absorbed energy (fluoresce) at this same wavelength. Unlike the directional excitation source, the fluorescence is omnidirectional and may thus be detected using a photomultiplier tube or UV photodiode. The technique differs from the more conventional atomic absorption (AA) technique in that it is more sensitive, more selective, and is linear over a wide range of concentrations. However, any molecular species present in the carrier gas will quench the fluorescence signal and for this reason, the technique is most commonly used with an inert carrier gas such as argon.