USGS-NWQL: I-2191-02: Laboratory arsenic speciation, phosphate mobile phase, arsine generation, ICP-MS detection, dissolved
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Official Method Name
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Laboratory arsenic speciation, phosphate mobile phase, arsine generation, ICP-MS 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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A phosphate buffer mobile phase is used to separate the arsenic species using high performance liquid chromatography. The method was optimized with a gradient using 38 mM and 75 mM phosphate buffer. Arsine generation is used to introduce the analytes into the ICP-MS, preventing salt build-up on the cones, eliminating chloride interferences, and improving the MDL. |
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Scope and Application
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This method is used to determine dissolved arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), and dimethylarsinate (DMA) in water. |
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Applicable Concentration Range
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MDL to 50 |
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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 biasing arsenic speciation results. This effect can be minimized by decreasing the pH to stabilize the cations or by complexation of the cations. Use of an 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. Spectral interference from argon-chloride molecular ion at m/z 75 when using ICP-MS to determine arsenic has been documented and suitable correction methods have been established. However, chromatographic separation minimizes chloride interference. Other hydride-forming elements and selected transition metals have been shown to be possible interferents for arsine generation reactions. However, such interference is minimized through the chromatographic separation. |
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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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90 days |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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