EPA-NERL: 350.3: Ammonia by Potentiometry
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Official Method Name
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Nitrogen, Ammonia (Potentiometric, Ion Selective Electrode) |
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Current Revision
| Issued 1974 |
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Media
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WATER |
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Instrumentation
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Ion Selective Electrode |
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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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Ammonia is determined potentiometrically using an ion-selective ammonia electrode and a pH meter having an expanded millivolt scale or a specific ion meter. The ammonia electrode uses a hydrophobic gas permeable membrane to separate the sample solution from an ammonia chloride internal solution. Ammonia in the sample diffuses through the membrane and alters the pH of the internal solution, which is sensed by a pH electrode. The constant level of chloride in the internal solution is sensed by a chloride selective ion electrode which acts as a reference electrode. |
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Scope and Application
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This method determines ammonia-nitrogen in drinking, surface, and saline waters; domestic and industrial wastes. |
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Applicable Concentration Range
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0.03 to 1400 mg/L ammonia as nitrogen. |
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Interferences
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(A) Volatile Amines: Volatile amines act as a positive interference (measured value is greater than the true value). (B) Mercury: Mercury forms a strong complex with ammonia. DO NOT preserve samples with mercuric chloride. |
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Quality Control Requirements
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None given. |
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Sample Handling
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Samples may be preserved with 2 mL of concentrated sulfuric acid and stored at 4oC. |
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Maximum Holding Time
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28 days (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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