EPA-NERL: 206.4: Arsenic by Spectrophotometry
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Official Method Name
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Arsenic (Spectrophotometric-SDDC) |
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Current Revision
| Issued 1971; Editorial Revision 1974 |
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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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Arsenic in the sample is reduced to arsine (arsenic trihydride) in acid solution in a hydrogen generator. The arsine is passed through a scrubber to remove sulfide and is absorbed in a solution of silver diethyldithiocarbamate dissolved in pyridine. The absorbance of the red complex that forms is proportional to arsenic concentration and is measured with a spectrophotometer. |
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Scope and Application
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This method determines inorganic arsenic in drinking water and most fresh and saline waters in the absence of high concentrations of chromium, cobalt, copper, mercury, molybdenum, nickel, and silver. Industrial wastes may be analyzed after digestion by EPA Method 206.5. |
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Applicable Concentration Range
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Above 10 ug/L. |
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Interferences
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(A) Odor: If pyridine odor is objectionable, 1-Ephedrine in chloroform can be use as a solvent for silver diethyldithiocarbamate. (B) Nitric acid: Nitric acid can produce a negative interference. Use sulfuric acid as a preservative if only inorganic arsenic is being measured. For additional interferences see EPA Methods 200.0 and 206.5. |
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Quality Control Requirements
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Spike industrial waste samples with a known amount of arsenic to establish adequate recovery. QC requirements for drinking water procedures are provided in method 200.0. |
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Sample Handling
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Use an air-tight system to avoid loss of arsenic during arsine evolution. Additional procedures are provided in EPA Method 206.5 and 200.0. |
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Maximum Holding Time
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6 months (MCAWW, Table 1). |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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200.0, 206.5 |
