EPA-NERL: 349.0: Ammonia in Estuarine and Coastal Waters by Colorimetry
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Official Method Name
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Determination of Ammonia in Estuarine in Coastal Waters by Gas Segmented Continuous Flow Colorimetric Analysis |
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Current Revision
| Revision 1.0, September 1997 |
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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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This method is based on the indophenol reaction and employs an automated gas-segmented continuous flow analysis system. A sample is introduced into the system, and ammonia in the sample reacts with alkaline phenol and NaDTT upon heating (and in the presence of a catalyst) to form indophenol blue. The concentration of ammonia in the sample is determined by measuring indophenol blue with a spectrophotometer; correcting for errors due to matrix through data processing. |
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Scope and Application
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This method determines total ammonia (NH3 and NH4+) in estuarine and coastal waters. |
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Applicable Concentration Range
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The method is linear up to 4 mg-N/L. |
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Interferences
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Interferences
(A) Hydrogen sulfide: Hydrogen sulfide > 2 mg/L should be removed by acidifying the sample and stripping with nitrogen. (B) Metals: Complex calcium and magnesium using sodium citrate or EDTA to prevent precipitation of calcium and magnesium hydroxides in alkaline reagent solution. (C) Turbidity: Remove turbidity using filtration. (D) Refractive index: Error due to difference in the refractive index of saline and reagent waters are corrected using salinity matching. |
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Quality Control Requirements
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Initial demonstration of performance, continued analysis of Laboratory Reagent Blanks (LRB), laboratory duplicates and Laboratory Fortified Blanks (LFB) with each set of samples as a continuing check on performance. |
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Sample Handling
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Samples collected using hydrocast or submersible pump systems. Turbid samples must be filtered through a 0.45 um membrane filter as soon as possible after collection. For sample storage use 60-mL glass or high density polyethylene bottles rinsed 3 times with about 20 mL of sample and shaken with the cap in place after each rinse. Pour the rinse water into the cap to dissolve and rinse away salt crusts trapped in the threads of the cap, fill the sample bottle to 3/4 full, and screw the cap on firmly. Samples should be stored at 4oC in the dark until analysis. No preservation technique is satisfactory for samples with ammonia concentrations > 20 ug N/L. For moderate to high concentrations of ammonia (> 20 ug N/L) samples can be preserved by the addition of 2 mL of chloroform per liter of sample. |
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Maximum Holding Time
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3 hours; 14 days for preserved estuarine and coastal water samples with moderate to high concentrations of ammonia |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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