Mercury by Cold-Vapor AA

National Geochemical Survey

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Analysis of Mercury by Cold Vapor Atomic Absorption Spectrometry (USGS and XRAL laboratories)

Method

100-mg sample aliquots are digested with a mixture of sulfuric acid, nitric acid, 5% potassium permanganate, and 5% potassium peroxydisuflate in a water bath for one hour. Excess potassium permanganate is reduced with hydroxylamine sulfate solution. Hg (II) is then reduced with stannous chloride. The Hg vapor is separated and measured using a LEEMAN PS200 automated mercury analyzer. Solutions derived from NIST standard reference material 1641c are used for calibration. Samples exceeding 1.8 ppm mercury require dilution. Details of the method are given in the references below. Analytical data for an experimental run are deemed acceptable based on results determined for two in-house quality-control standards: recovery for all elements present at >5 times the detection limit must be within 20% of the certified value, and the calculated relative standard deviation for duplicate samples is no greater than 20%. Details may be found in O'Leary and others (1996) and Brown and others (2002a).

Data analysis

Important note: Mercury is a difficult element for which to obtain accurate analyses. Samples can easily be contaminated with Hg during handling, storage, and preparation for analysis. Mercury can also be lost from samples during the drying process or while in storage. Recently collected samples were handled and stored in a manner that should result in few such problems. However, many Hg data in the NGS are based on reanalyses of archival samples, e.g., NURE samples, that were neither collected using protocols appropriate for Hg analysis, nor stored under conditions that would necessarily preserve the original Hg concentrations. Some NURE samples in the eastern US were very likely contaminated by Hg at some point after collection (e.g., all samples from Allegany County, Maryland). At the present time, it is not known which archival samples may have been contaminated with Hg in the laboratory, and thus extreme caution should be exercised in interpreting NGS data.

		Distribution maps
Element	QA/QC	Conter- minous	Alaska	Hawai`i
Hg (ppm)	In progress

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U.S. Department of the Interior, U.S. Geological Survey
This page is part of U.S. Geological Survey Open-File Report 2004-1001
URL: http://www-tin.er.usgs.gov/geochem/doc/mercury.htm
Maintained by Jeff Grossman
Last modified: 15:03:11 Tue 06 Jan 2004
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