EPA-NERL: 351.4: TKN by ISE
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Official Method Name
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Nitrogen, Kjeldahl Total (Potentiometric, Ion Selective Electrode) |
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Current Revision
| Issued 1978 |
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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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A sample is digested according to one of three procedures (macro-Kjeldahl, micro-Kjeldahl, or Block Digestion) to convert total Kjeldahl nitrogen (TKN) into ammonia. Following digestion and cooling, distilled water is added to the digestion flask and the pH adjusted to between 3 and 4.4 by the addition of NaOH. The sample is cooled and transferred to a 100 mL beaker. NaOH-NaI-EDTA is added to the beaker, and the ammonia concentration is measured using an ion selective electrode (EDTA prevents precipitation of hydroxides, thereby preventing deposition on the electrode membrane). |
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Scope and Application
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This method is applicable to the measurement of total Kjeldahl nitrogen (TKN) in drinking and surface water; domestic and industrial waste. |
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Applicable Concentration Range
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0.03 to 25 mg-TKN/L. |
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Interferences
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(A) Metals: Interference from metals is eliminated by the addition of NaI. (B) Nitrate: High nitrate concentrations (> 10 times the TKN level) result in low TKN values because of reaction between nitrate and ammonia. The reaction can be prevented by the use of an anion exchange resin (chloride form) to remove the nitrate prior to TKN analysis. |
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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 by adding 2 mL of concentrated sulfuric acid per liter of sample and storing at 4oC. However, even with preservation organic nitrogen can convert to ammonia. Therefore, analyze samples 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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