Traceability of the output concentration of mercury vapor generators

In response to the environmental impact of mercury and the neuro-toxic risk associated with trophic transfer of methyl mercury to humans, the reduction of mercury emissions from coal-fired electric utilities, a significant anthropogenic source, is now receiving global attention. To address impending regulations for mercury reduction, there is a need to establish a mercury emissions measurement framework, which has demonstrated accuracy and traceability to national and international standards. To support this effort, the National Institute of Standards and Technology (NIST) has been working jointly with the United States Environmental Protection Agency (EPA) to develop a traceability system which links the output of elemental mercury calibration instrumentation sited at the power utilities, to the SI (International System of Units). This system is based on a reference (NIST Prime) elemental mercury generator standard, which is used by NIST to certify elemental mercury generators from the instrument vendors. These in turn are used by the instrument vendors to provide NIST traceable calibration for the instrumentation supplied to each electric utility. The NIST Prime generator is certified using a primary analytical method for the determination of mercury using sorbent trap analysis with isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS).