USGS Test Method I-2464-01


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Source:
USGS

Method Name:
Organic plus Inorganic Mercury in Filtered Natural Water by Cold-Vapor AFS. Official Name: Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Determination of Organic Plus Inorganic Mercury in Filtered and Unfiltered Natural-Water with CV-AFS

Description:
Concentrations of organic plus inorganic mercury in filtered natural-water samples are determined by CV-AFS. The method is based on U.S. Environmental Protection Agency (1999) Method 1631, but does not use gold amalgamation for mercury preconcentration. By eliminating the preconcentration procedure, the MDL is at least a factor of 10 greater, yet the method provides the determination of mercury at ambient concentrations. Mercury species in a natural-water sample are oxidized to mercury (II) inside the borosilicate-glass sample bottle by using bromine monochloride; excess oxidant is neutralized with hydroxylamine hydrochloride. Mercury (II) is reduced to elemental mercury by using stannous chloride, and is purged from the solution with ultrapure argon gas into a cell in which the mercury concentration is measured by atomic fluorescence emission at 253.7 nm.

Scope:
This method is used to determine concentrations of organic plus inorganic mercury in filtered natural-water samples. Bromine monochloride is used to oxidize elemental mercury, mercury complexes, various alkyl- and phenyl-mercury compounds, and other forms of mercury. The upper limit of the linear concentration is 125 ng/L mercury. The short-term method detection limit is 5 ng/L mercury.

Citation:
Garbarino, J.R., and Damrau, D.L., 2001, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of organic plus Inorganic mercury in filtered and unfiltered natural water with cold vapor--automatic fluorescence spectromety: U.S. Geological Survey Water-Resources Investigations Report 01-4132.

Interferences:
Contamination must be avoided because of the inherently low mercury concentration found in natural water. Gold, silver, and iodide interfere with the determination of mercury by this method. Buildup of condensation in the vapor generator or fluorescence cell will degrade the analytical signal. Ultrapure argon (99.998) percent must be used for the purge gas to minimize the possibility of fluorescent quenching by impurities.

QC Requirements:
Quality-control samples area analyzed at a minimum of one in every ten samples. These QC samples include at least one of each of the following: blanks, quality control samples, third party check solutions, replicates, and spikes. Correlation coefficients for calibration curves must be at least 0.99. QC samples must fall within 1.5 standard deviations of the mean value. If all of the data-acceptance criteria in the SOPs are met, then the analytical data are acceptable.

Maximum Holding Time:
180 days from sampling

Media:
WATER

Subcategory:
Inorganic

Concentration:
5 - 125

Precision:
The percentage recovery of results for various concentrations of mercury spiked into reagent water, filtered water, and filtered ground water was used to validate the method. Data were acquired during 7 nonconsecutive days. No more than two sets of data were acquired in 1 day. The range of average percent recovery for all filtered and unfiltered matrices at 20, 45, and 75 ng/L was 89 to 108, 96 to 103, and 94 to 98 percent, respectively. The variability in the recovery of 20 ng/L, a concentration about four times the short-term MDL, was about twice that of higher spike concentrations. In addition, the variability in recoveries at 20 ng/L for the unfiltered matrices was about twice those for corresponding filtered matrices. There was little difference, however, in variability for filtered and unfiltered matrices for spike concentrations of 45 to 75 ng/L.

Detection:
Method detection limits (MDLs) were determined for this method using the procedures of the U.S. Environmental Protection Agency (1997).

Revision Number:
2001

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