EPA-ORD / EPA-OST: 245.7: Mercury in water by cold-vapor atomic fluorescence spectrometry
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Official Method Name
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Mercury in water by cold-vapor atomic fluorescence spectrometry |
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Current Revision
| Revision 2.0, February 2005 |
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Media
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WATER |
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Instrumentation
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Cold Vapor Atomic Fluoresence Spectrophotometer |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Method 245.7: Mercury in Water by Cold Vapor Atomic Fluorescence Spectrometry, Revision 2.0, February 2005, EPA-821-R-05-001. |
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Brief Method Summary
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A 100- to 2,000-mL sample is collected directly into a specially cleaned, pretested, fluoropolymer bottle using sample handling techniques specially designed for collection of mercury at trace levels. For dissolved Hg, the sample is filtered through a 0.45-um capsule filter prior to preservation. The sample is preserved by adding 5 mL/L of pretested 12N HCl. If a sample also will be used for the determination of methyl mercury, it should be preserved according to procedures in the method that will be used for detection of methyl mercury. Prior to analysis, all Hg in a sample is oxidized by a potassium bromate/potassium bromide reagent. After oxidation, the sample is sequentially pre-reduced with NH2OH.HCl to destroy the excess bromine, then the ionic Hg is reduced with SnCl2 to convert Hg(II) to volatile Hg(0). The Hg(0) is separated from solution by passing the sample through a gas/liquid separator and purging with high purity argon gas. The Hg passes into an inert gas stream that carries the released Hg(0) into the cell of a cold-vapor atomic fluorescence spectrometer for detection. The concentration of Hg is determined by atomic fluorescence spectrometry at 253.7 nm. Quality is assured through calibration and testing of the oxidation, purging, and detection systems. |
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Scope and Application
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This method is for the determination of mercury in filtered and unfiltered drinking water, surface and ground waters, marine water, and industrial and municipal wastewater. |
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Applicable Concentration Range
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5-100 ng/L, may be extended by dilution of the sample |
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Interferences
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Gold, silver and iodide are known interferences. See method for steps to reduce interferences.
The use of a brominating digestion coupled with atomic fluorescence detection overcomes many of the chloride, sulfide and molecular absorption interferences. No interferences have been noted for sulfide concentrations below 24 mg/L. High purity argon (99.998%) must be used as the carrier gas. Using nitrogen may reduce the sensitivity by a factor of eight fold, while the use of air may reduce the sensitivity thirty fold. Water vapor may collect in the fluorescence detector cell, resulting in a degradation of the analytical signal or giving a false peak due to scattering of the excitation radiation. The use of a membrane drying tube is required to reduce quenching and to remove any water vapor from the transfer tubing that can contaminate the detector. |
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Quality Control Requirements
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Each laboratory that uses this method is required to operate a formal quality assurance program. The minimum requirements of this program consist of an initial demonstration of laboratory capability, ongoing analysis of standards and blanks as a test of continued performance, and the analysis of matrix spikes (MS) and matrix spike duplicates (MSD) to assess accuracy and precision. Laboratory performance is compared to established performance criteria to determine that the results of analyses meet the performance characteristics of the method. |
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Sample Handling
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Before samples are collected, consideration should be given to the type of data required so that appropriate preservation and pretreatment steps can be taken. An excess of KBr/KBrO3 should be confirmed to ensure the sample has been properly preserved. Samples are collected into rigorously cleaned fluoropolymer bottles with fluoropolymer or fluoropolymer-lined caps. It is critical that the bottles have tightly sealed caps to avoid diffusion of atmospheric Hg through the threads. Polyethylene sample bottles must not be used. Sample filtration: For dissolved Hg, filter through a 0.45-um capsule filter in a mercury-free area prior to preservation. If the sample is filtered, it must be accompanied by a blank that has been filtered under the same conditions. Preservation: Samples are preserved by adding 5 mL/L of pretested 12 N HCl. If a sample also will be used for the determination of methyl mercury, it should be collected and preserved according to procedures in the method that will be used for determination of methyl mercury. Samples may be shipped to the laboratory unpreserved if they are collected in fluoropolymer or glass bottles and capped tightly. The samples must be acid-preserved within 48 h of collection. Samples for dissolved Hg must be filtered before preservation. Samples that are acid-preserved may lose Hg to coagulated organic materials in the water or condensed on the bottle wall. The best approach is to add KBrO3/KBr directly to the sample bottle at least 24 hours before analysis. If other Hg species are to be analyzed, aliquots must be removed prior to addition of KBrO3/KBr. If KBrO3/KBr cannot be added directly to the sample bottle, the bottle must be shaken vigorously prior to sub-sampling. Storage:Sample bottles should be stored in clean (new) polyethylene bags until analysis. |
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Maximum Holding Time
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90 days |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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Method 1669 |
