Cold Vapor Atomic Fluorescence (CVAF) is a powerful technique based on detecting fluorescence light emitted by the sample. Below the principle of the technique is explained in a nutshell.
First of all, a UV light source is needed. A mercury vapor lamp is used as the UV light source, and the light is directed to the sample cell. When the sample gas enters the sample cell, the Hg atoms in the gas are excited by the UV light.
Right after, the excited Hg atoms re-radiate the absorbed energy, which is called fluorescence. Fluorescence light is omnidirectional, which means that the light is emitted in all directions. Therefore, detector is usually placed at 90° angle to the light source to ensure that only the fluorescence light is detected. The detector is a photon-counting module, which will only detect the photons derived from the Hg atoms.
The CVAF technique is an extremely selective technique with a high sensitivity, which ensures accurate measurement of extremely low mercury levels. Low detection limit of CVAF also enables diluting the stack gas. With dilution, cross-interference effects from other gases like SO2 and O2 can be eliminated.
- Highest sensitivity
- Extremely selective
- Future-proof technique
Gasmet Continuous Mercury Monitoring system CMM incorporates CVAF technique with special Gasmet design, which enables measuring the lowest mercury levels from hot, wet and corrosive gas streams.
The sample cell is directly connected to a thermal converter, which converts all mercury compounds to elemental mercury before the measurement. This way recombination of mercury compounds is eliminated and total gaseous mercury measurement achieved. The detector used in Gasmet CMM is an extremely sensitive photon counting module. Furthermore, the Gasmet CVAF sample cell design includes light traps to eliminate any stray light reflections to the detector.
Gasmet CMM has successfully completed the EN15267-3 testing with the world’s lowest EN15267 certified range (0 to 5 µg/m3) for continuous mercury measurement. This new world record makes our CMM future-proof for declining emission limits! Read more about our certified CMM system here.