EPA-NERL: 351.3 (Nesslerization): Total Kjeldahl Nitrogen by Colorimetry
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Official Method Name
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Nitrogen, Kjeldahl Total (Colorimetric; Titrimetric; Potentiometric) |
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Current Revision
| Editorial Revision 1974, 1978 |
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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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The sample is heated in the presence of sulfuric acid, potassium sulfate, and mercuric sulfate, and evaporated until sulfite fumes are obtained and the solution becomes colorless or pale yellow. The residue is cooled, diluted, and is treated and made alkaline with a hydroxide-thiosulfate solution. The ammonia is distilled and determined after distillation by Nesslerization or other procedure. |
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Scope and Application
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This method determines Kjeldahl nitrogen in drinking, surface, and saline waters; domestic and industrial wastes. The method may not capture all nitrogenous compounds (e.g., some amines, nitro compounds, hydrozones); consult the method for more information. |
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Applicable Concentration Range
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Below 1 mg/L |
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Interferences
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Nitrate: High nitrate levels (> 10 times the TKN level) result in low TKN values. The reaction between nitrate and ammonia can be prevented by using an anion exchange resin (chloride form) to remove the nitrate prior to the TKN analysis. |
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Quality Control Requirements
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None. |
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Sample Handling
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Cool to 4oC, and add 2 mL of H2SO4. Even with preservation, organic nitrogen can convert to ammonia. Therefore, analyze as soon as possible. |
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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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