EPA-NERL: 351.3 (Nesslerization):  Total Kjeldahl Nitrogen by Colorimetry

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
Nitrogen, Kjeldahl Total (Colorimetric; Titrimetric; Potentiometric)
Current Revision
Editorial Revision 1974, 1978
Media
WATER
Instrumentation
Spectroscopy (Colorimetry; Photometry)
Method Subcategory
Inorganic
Method Source
  EPA-NERL
Citation
  Methods for the Chemical Analysis of Water and Wastes (MCAWW) (EPA/600/4-79/020)
Brief Method Summary
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.
Scope and Application
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.
Applicable Concentration Range
Below 1 mg/L
Interferences
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.
Quality Control Requirements
None.
Sample Handling
Cool to 4oC, and add 2 mL of H2SO4. Even with preservation, organic nitrogen can convert to ammonia. Therefore, analyze as soon as possible.
Maximum Holding Time
28 days (MCAWW, Table 1).
Relative Cost
Less than $50
Sample Preparation Methods