Cold vapour atomic fluorescence spectroscopy
Cold vapour atomic fluorescence spectroscopy (CVAFS) is a subset of the analytical technique known as atomic fluorescence spectroscopy (AFS).
Use for mercury detection
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 vapour measurement at room temperature. Free mercury atoms in a carrier gas are excited by a collimated ultraviolet light source at a wavelength of 253.7 nanometres. 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.
Gold coated traps may be used to collect mercury in ambient air or other media. The traps are then heated, releasing the mercury from the gold while passing argon through the cartridge. This preconcentrates the mercury, increasing sensitivity, and also transfers the mercury into an inert gas.
A number of companies have commercialized mercury detection via CVAFS and produced transportable analysers capable of measuring mercury in ambient air. These devices can measure levels in the low parts per quadrillion range (10−15).
Various analytical methods approved by the United States Environmental Protection Agency (EPA) for measuring mercury in wastewater are in common use. EPA Methods 245.7 and 1631 are commonly used for measurement of industrial wastewater using CVAFS.
Other analytical techniques suitable for analyzing heavy metals in air or water:
- Kopysc, Edyta; Pyrzynska, Krystyna; Garbos, Slawomir; Bulska, Ewa (July 21, 2000). "Determination of Mercury by Cold-Vapor Atomic AbsorptionSpectrometry with Preconcentration on a Gold-Trap". Analytical Sciences. 16 (December 2000): 1309–1312. doi:10.2116/analsci.16.1309. Retrieved April 21, 2016.
- "Method 245.7. Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry; Rev. 2.0". Clean Water Act Analytical Methods. Washington, DC: US Environmental Protection Agency (EPA). February 2005. EPA 821-R-05-001.
- "Method 1631. Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry; Rev. E". Clean Water Act Analytical Methods. EPA. August 2002. EPA 821-R-02-019.