Standard Methods: 4500-NorgB: Nitrogen, organic, in Water by Macro-Kjeldahl
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Official Method Name
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Macro-Kjeldahl 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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Titration |
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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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In the presence of sulfuric acid, potassium sulfate, and cupric sulfate catalyst, amino nitrogen of many organic materials is converted to ammonia. Free ammonia also is converted to ammonium. After addition of base, the ammonia is distilled from an alkaline medium and absorbed in boric or sulfuric acid. The ammonia may be determined colorimetrically, by ammonia-selective electrode, or by titration with a standard mineral acid. |
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Scope and Application
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This method covers the determination of organic nitrogen in surface waters, domestic and industrial wastes. |
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Applicable Concentration Range
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0 to 100 mg/L |
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Interferences
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Nitrate in excess of 10 mg/L. Large amounts of acids or salts may increase the digestion temperature to a point where pyrolytic loss of nitrogen begins to occur. |
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Quality Control Requirements
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None given |
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Sample Handling
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The most reliable results are obtained on fresh samples. If an immediate analysis is not possible, preserve samples for kjeldahl digestion by acidifying to pH 1.5 to 2.0 with concentrated H2SO4 and storing at 4oC. After sample size is selected, dilute sample to 300 mL, neutralize to pH 7, and add sodium thiosulfate dechlorinating agent equivalent to the chlorine residual. |
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Maximum Holding Time
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7 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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