NEMI Method Summary

Method Summary Information

Method Number: 351.4 Media: WATER
Revision: Issued 1978
Method Source: U.S. EPA National Exposure Research Laboratory (NERL) [formerly EMSL]
Analytes in this method
Subcategory: INORGANIC
Official Name: Nitrogen, Kjeldahl Total (Potentiometric, Ion Selective Electrode)
Descriptive Name TKN by ISE
Source Info: U.S.EPA National Exposure Research Laboratory (NERL)
Microbiological and Chemical Exposure Assessment Research Division (MCEARD)
[formerly the Environmental Monitoring Systems Laboratory (EMSL), Cincinnati, OH]
26 West Martin Luther King Drive
Cincinnati, Ohio 45268-0001
Fax: 513-569-7757
email: DWmethods.help@epa.gov
Citation: Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
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Brief Method
Summary:
 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).
Scope And
Application:
 This method is applicable to the measurement of total Kjeldahl nitrogen (TKN) in drinking and surface water; domestic and industrial waste.
Applicable
Conc Range:
 0.03 to 25 mg-TKN/L.
Interferences: (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.
QC Requirements: None given.
Sample Handling: 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.
Max Holding Time:
 28 days (MCAWW, Table 1).
 
Relative Cost: Less than $50
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