Standard Methods: 3500-As B: Arsenic by Silver Diethyldithiocarbamate
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Official Method Name
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3500-As B. Silver Diethyldithiocarbamate Method |
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Current Revision
| Standard Methods Online |
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Media
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WATER |
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Instrumentation
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Spectroscopy (Colorimetry; Photometry) |
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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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Brief Method Summary
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Arsenite, containing trivalent arsenic, is reduced selectively by aqueous sodium borohydride solution to arsine in an aqueous medium of pH 6. The generated arsine is swept by a stream of oxygen-free nitrogen from the reduction vessel through a scrubber containing glass wool or cotton impregnated with lead acetate soution into an absorber tube containing silver diethyldithiocarbamate and morpholine dissolved in chloroform. The intensity of the red color that develops is measured at 520 nm. |
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Scope and Application
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The method is applicable to the determination of total inorganic arsenic when interferences are absent and when the sample contains no methylarsenic compounds. This method can also identify and quantify arsenate and arsenite separately by generating arsine at different pHs. |
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Applicable Concentration Range
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Interferences
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Although certain metals - chromium, cobalt, copper, mercury, molybdenum, nickel, platinum, silver, and selenium - influence the generation of arsine, their concentrations in water seldom are high enough to interfere. H2S interferes, but the interference is removed with lead acetate. Antimony is reduced to stibine, which forms a colored complex with an absorption maximum at 510 nm and interferes with the arsenic determination. Methylarsenic compounds are reduced at pH l to methylarsines, which form colored complexes with the absorber solution. If methylarsenic compounds are present, measurements of total arsenic and arsenate are unreliable. The results for arsenite are not influenced by methylarsenic compounds. |
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Quality Control Requirements
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See Section 3020 Quality Assurance/Quality Control. |
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Sample Handling
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Plastic or glass containers. Add HNO3 to pH <2. See Section 3010 for more details. |
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Maximum Holding Time
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6 months (See Section 1060) |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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