EPA-ORD / EPA-OST: 351.2: Total Kjeldahl nitrogen in water by semiautomated colorimetry

Summary
Analytes
Revisions
Data and Sites

Official Method Name

Method 351.2: Determination of Total Kjeldahl nitrogen by semi-automated colorimetry

Current Revision

Revision 2.0, August 1993

Media

WATER

Instrumentation

Colorimeter

Method Subcategory

Inorganic

Method Source

EPA-ORD / EPA-OST

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, H₂SO₄ for two and one half hours.The residue is cooled, diluted to 25 mL and analyzed for ammonia.This digested sample may also be used for phosphorus determination.
Total Kjeldahl nitrogen is the sum of free-ammonia and organic nitrogen compounds which are converted to ammonium sulfate (NH₄)₂SO₄, under the conditions of digestion described.
Organic Kjeldahl nitrogen is the difference obtained by subtracting the free ammonia value from the total Kjeldahl nitrogen value.
Reduced volume versions of this method that use the same reagents and molar ratios are acceptable provided they meet the quality control and performance requirements stated in the method.

Scope and Application

This method covers the determination of total Kjeldahl nitrogen in drinking, ground, and surface waters, domestic and industrial wastes.The procedure converts nitrogen components of biological origin such as amino acids, proteins and peptides to ammonia, but may not convert the nitrogenous compounds of some industrial wastes such as amines, nitro compounds, hydrazones, oximes, semicarbazones and some refractory tertiary amines.

Applicable Concentration Range

0.1-20

Interferences

High nitrate concentrations (10X or more than the TKN level) result in low TKN values.If interference is suspected, samples should be diluted and reanalyzed.
Method interferences may be caused by contaminants in the reagent water, reagents, glassware, and other sample processing apparatus that bias analyte response.

Quality Control Requirements

Demonstration of laboratory capability, and periodic analysis of laboratory reagent blanks, fortified blanks, and other laboratory solutions as a continuing check on performance.

Sample Handling

Samples should be collected in plastic or glass bottles. All bottles must be thoroughly cleansed and rinsed with reagent water.
Samples must be preserved with H₂SO₄ to a pH < 2 and cooled to a 4^oC at the time of collection.
Samples should be analyzed as soon as possible after collection. If storage is required, preserved samples should be maintained at 4^oC.

Maximum Holding Time

28 days

Relative Cost

Less than $50

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Total Kjeldahl nitrogen(E-10264) Kjeldahl nitrogen, total Nitrogen, Kjeldahl, total Nitrogen, organic TKN Total Kjeldahl nitrogen	0.100 mg/L	102% Rec (ML)	19.30 % RSD (ML)			0.38 mg/L

Precision Descriptor Notes:	Precision and accuracy values were calculated using interlaboratory data from performance evaluation studies.
Detection Level Note:	MDL is established using reagent water fortified at a concentration of 2 to 3 times the estimated instrument detection limit and is determined from 7 replicate aliquots of the fortified reagent water and processed through the entire analytical method.

Revision	PDF/Link
Revision 2.0, August 1993
Issued 1978

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EPA-ORD / EPA-OST: 351.2: Total Kjeldahl nitrogen in water by semiautomated colorimetry

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