USGS-NWQL: I-1190-02: Arsenic, dissolved, field speciation, solid-phase extraction, ICP-MS
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Official Method Name
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Field arsenic speciation, solid-phase extraction, inductively coupled plasma-mass spectrometry detection, dissolved |
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Current Revision
| 2002 |
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Media
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WATER |
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Instrumentation
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Inductively Coupled Plasma - Mass Spectrometry |
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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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Garbarino, J.R., Bednar, A.J., and Burkhart, M.R., Methods of Analysis of the U.S. Geological Survey National Water Quality Laboratory -- Arsenic Speciation in Natural-Water Samples Using Laboratory and Field Methods, U.S. Geological Survey Water-Resources Investigations Report 02-4144, 47 p. |
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Brief Method Summary
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Arsenic species are separated in the field by using a syringe to elute 10 mL of EDTA-preserved sample through a LC-SAX cartridge that has been conditioned with 2 mL of methanol followed by 10 mL of reagent water prior to use. Charged arsenic species are retained on the cartridge. The cartridge and elutriate are retained for laboratory arsenic determination. The charged arsenic species are stripped from the cartridge in the laboratory with 10 mL of 0.16 M nitric acid. The extract and elutriate are analyzed for total arsenic using direct nebulization ICP-MS. |
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Scope and Application
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This method is used to determine dissolved arsenite (As(III)) and arsenate (As(V)) in water. |
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Applicable Concentration Range
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MDL to 100 |
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Interferences
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Chemical and spectral interferences can affect the accuracy of determining arsenic species unless appropriate procedures are followed. Iron and manganese oxyhydroxide precipitates provide sorption sites for dissolved arsenic species that might negatively bias arsenic speciation results. This effect can be minimized by decreasing the pH to stabilize the cations or by complexation of the cations. Use of a EDTA preservative works best for a wide range of sample matrices. As(III) can be oxidized to As(V) by photolytically produced free radicals. Opaque polyethylene sample bottles are used to eliminate this effect. Additionally, As(V) concentrations can be positively biased when the sample matrix contains monomethylarsonate (MMA) or dimethylarsinate (DMA). These arsenic species are retained on the cartridge with As(V) and further laboratory separation is requred to accurately assess the arsenic species concentrations. Lastly, anions present in the sample matrix compete with the arsenic species for exchange sites within the cartridge. When the exchange capacity of the cartridge is exceeded, the As(V) is not retained fully on the cartridge and elutes as apparent As(III). The exchange capacity has not been found to be a limitation for most surface- and ground-water samples. Spectral interference from argon-chloride molecular ion at m/z 75 when using ICP-MS to determine arsenic has been documented and suitable correction have been established. |
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Quality Control Requirements
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Calibrate instrument using calibration standards (CAL); quality control samples (QCS); and laboratory blanks (LB) analyzed at a minimum of 1 for every 10 samples. |
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Sample Handling
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Container Description: opaque polyethlyene bottle. Handling and Treatment: Filter at 0.45 um and preserve with EDTA. |
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Maximum Holding Time
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Cartridge 30 days prior to extraction; 90 days for extract and elutriate |
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Relative Cost
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Sample Preparation Methods
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