|
Flett Research Ltd
440 DeSalaberry Avenue, Winnipeg MB CANADA Phone/Fax: (204) 667-2505 |
|
|
|
|
|
|
|
|
|
|
| >>FLETT HOME PAGE >> MERCURY >> METHODS |
Flett Research - Mercury Methods Total Mercury Methods Total mercury measurements are based upon the SnCl 2 reduction method, gold amalgam trapping, with fluorescence detection (EPA1631e). Total Mercury in Aqueous samples - The methods used here at Flett are based upon earlier work of Fitzgerald and Gill (1979), Bloom and Crecelius (1983), Gill and Fitzgerald (1985), and Bloom and Fitzgerald (1988). They have been in use in our laboratory since 1991. Essentially identical methodology (Method 1631) was adopted by the US EPA in 1996. Our laboratory was one of about a dozen labs worldwide that participated in the validation of the method under contract to EPA. Metallic mercury (Hg0) is sparingly soluble in water and has a significant vapour pressure at room temperature. It is therefore a suitable candidate for extraction and concentration by purge and trap methodology. The metallic vapour readily fluoresces under irradiation from a mercury vapour lamp, a property that allows for very sensitive and specific detection of the element by cold vapour atomic fluorescence spectrometry. Elemental mercury is done similarly, but SnCl 2 is omitted. Total Mercury in tissue and sediment - The methodology is a modification of US EPA's method 1631e for the determination of total Hg in aqueous samples. The method for the preparation of sample material by acid digestion is based on, but not identical to, published procedures by Hendzel and Jamieson (1976), and Horvat, Bloom and Liang (1993) and others. Total Hg in sediment and tissue is also measured using a DMA-80 analyser according to a modification of EPA Method 7473. Controlled heating in an oxygenated decomposition furnace is used to liberate mercury from solid samples in the instrument. The sample is dried and then thermally and chemically decomposed within the decomposition furnace. The decomposition products are carried by flowing oxygen to the catalytic section of the furnace. Here oxidation is completed and halogens and nitrogen/sulfur oxides are trapped. The remaining decomposition products are then carried to an amalgamator that selectively traps mercury. After the system is flushed with oxygen to remove any remaining gases or decomposition products, the amalgamator is rapidly heated, releasing mercury vapor. Flowing oxygen carries the mercury vapor through absorbance cells positioned in the light path of a single wavelength atomic absorption spectrophotometer. Absorbance (peak height or peak area) is measured at 253.7 nm as a function of mercury concentration. Methyl Mercury Methods Methyl mercury (CH3Hg) measurements employ an ethylation step followed by purge and trap/GC separation and fluorescence detection (EPA1630). Methyl mercury in water - The methodology for both filtered and unfiltered water is by distillation, aqueous phase ethylation, purge & trap, thermal desorption, and cold-vapour atomic fluorescence spectrometry (CVAFS). The method is based on draft EPA method 1630 and work completed by the Florida Department of Environmental Protection Bureau of Laboratories (2011). Methyl mercury in tissue and sediment - The analytical methodology used is a modification of the draft EPA Method 1630 for the determination of methyl mercury in aqueous samples. Adaptations have been made to that method for use of distillation of sediment or KOH-MeOH digestion of tissues based on peer-reviewed, published procedures for the determination of CH3Hg (Horvat et all 1993)and work completed by the Florida Department of Environmental Protection Bureau of Laboratories (2011). Method References: EPA Method 1631 Revision E EPA Method 1630 EPA Method 7473 EPA Method 1669 Florida Department of Environmental Protection Other References: Fitzgerald, W.F.; Gill, G.A. "Sub-Nanogram Determination of Mercury by Two-Stage Gold Amalgamation and Gas Phase Detection Applied to Atmospheric Analysis," Anal. Chem. 1979, 15, 1714. Bloom, N.S; Crecelius, E.A. "Determination of Mercury in Sea water at Subnanogram per Liter Levels," Mar. Chem. 1983, 14, 49. Gill, G.A.; Fitzgerald, W.F. "Mercury Sampling of Open Ocean Waters at the Picogram Level," Deep Sea Res 1985, 32, 287. Bloom, N.S.; Fitzgerald, W.F. "Determination of Volatile Mercury Species at the Picogram Level by Low-Temperature Gas Chromatography with Cold-Vapor Atomic Fluorescence Detection," Anal. Chim. Acta. 1988, 208, 151. Guidance on the Documentation and Evaluation of Trace Metals Data Collected for Clean Water Act Compliance Monitoring, U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Engineering and Analysis Division (4303), 401 M Street SW, Washington, DC 20460, July 1996, EPA 821-B-96-004. "Results of the EPA Method 1631 Validation Study," February, 1998. Available from the EPA Sample Control Center, 6101 Stevenson Avenue, Alexandria, VA, 22304; 703/461-2100. Hendzel, M. and Jamieson, D. 1976. “Determination of mercury in fish.” Anal. Chem. 48 : 926 - 928 . Horvat, M., Bloom, N. S., Liang, L. 1993. “Comparison of distillation with other current isolation methods for the determination of methyl mercury compounds in low level environmental samples. Part 1. Sediments.” Analytica Chimica Acta. 281: 135-152. Bloom, N.S.; Horvat, M.; Watras, C.J. "Results of the International Mercury Speciation Intercomparison Exercise," Wat. Air. Soil Pollut., 1995, 80, 1257. For additional information, contact Dr. Robert Flett at flett@flettresearch.ca Return to the Flett Research Mercury Page. |
Flett Research Ltd - 440 DeSalaberry Ave - Winnipeg Manitoba CANADA R2L 0Y7 |
Phone/Fax: (204) 667-2505 |