Importance of Ultra-Trace Mercury Analysis in Gaseous Matrices
Mercury emissions into ambient air are predominantly Total Gaseous Mercury, Hg0 (TGM also includes small amount of reactive mercury and particulate mercury). Global inventories for mercury emissions to air from human activities and sources are still rising. Anthropogenic activities such as stationary combustion sources like coal-fired power plants and active chemical production industries that release mercury are among the many factors that increase mercury levels in ambient air.
Elemental mercury being the least water-soluble and persistent, tends to cycle worldwide before undergoing photochemical oxidation to deposit into ecosystems. Once it enters the aquatic system, it methylates (into a potent neurotoxin) and bioaccumulates in wildlife and the human food chain. Therefore, it is crucial to measure and monitor TGM to manage mercury and minimize its biogeochemical cycling.
Apart from ambient air, natural gas also contains trace levels of Mercury. Geologically, Mercury exists in the earth’s crust along with crude oil and natural gas.
Potential work safety hazard
During natural gas processing, if trace levels of Mercury are left unmonitored, they will cause Liquid Metal Embrittlement (LME) to the liquefaction plant structure, compromising the facility and workers safety. Therefore, it is crucial to verify that the mercury level is below the permittable threshold value for natural gas processing and operational integrity.
Potential household exposure to Mercury
For LPG, either propane (C3) or butane (C4) is mainly produced from crude oil refining or natural gas processing. Elemental mercury gas primarily exists in LPG. As LPG is commonly used as domestic cooking gas in the household, Hg0 can be emitted into the home and air unknowingly. Long-term exposure to Mercury will lead to bioaccumulation of Mercury levels in our body, causing various health effects.
Therefore, it is necessary to measure and control mercury content in LPG for human health safety and environmental protection.
How Does It Work?
For WA-Series in NIC, both models of WA use the same working principle of Dual-Gold Amalgamation to collect and purify mercury, with a choice of different detector for measurement. Model WA-5A is equipped with Cold Vapor Atomic Absorption Spectroscopy (CVAAS) detector while Model WA-5F comes with Cold Vapor Atomic Fluorescence Spectroscopy (CVAFS) detector.
It is named Dual-Gold Amalgamation as the mercury analytes go through two steps of gold amalgamation for sampling and enhancement, respectively. Both models perform direct analysis of mercury collector tube (also commonly known as Gold Amalgam Tube). It has excellent affinity and is highly selective towards Mercury.
Operating Principle at A Glance
This 1st amalgamation activity occurs during sampling when the gaseous sample is flowing through the mercury collector (sampling) tube. Mercury from the gaseous stream is trapped and concentrated as gold-amalgam.
Upon completion of sampling, the mercury collector (sampling) tube is brought to the WA-5. With precise temperature control, the sampling tube is thermally desorbed, releasing all trapped elemental Mercury.
2nd Gold amalgamation
The released elemental Mercury is directed to the Analytical Trap, located in WA-5. The Mercury is re-amalgamated to enhance the purification of mercury analytes, before transferring to the detector for measurement.
The analytical trap is subsequently heated. The elemental Mercury is released and transported to the optical path of CVAAS or CVAFS (argon is needed as the carrier gas) for measurement at 253.7nm.
Applications of WA-Series
WA-Series mercury analyzer can be used to analyze: