Standard Methods: 4500-NH₃ E: Ammonia by Selective Electrode Methods Using Known Addition

Summary
Analytes
Revisions
Data and Sites

Official Method Name

4500-NH₃ E. Ammonia-Selective Electrode Methods Using Known Addition

Current Revision

Standard Methods Online

Media

WATER

Instrumentation

Ion Selective Electrode

Method Subcategory

Inorganic

Method Source

Standard Methods

Citation

Standard Methods Online - Standard Methods for the Examination of Water and Wastewater

Brief Method Summary

When a linear relationship exists between concentration and response, known addition is convenient for measuring occasional samples because no calibration is needed. Because an accurate measurement requires that the concentration at least double as a result of the addition, sample concentration must be known within a factor of three. Total concentration of ammonia can be measured in the absence of complexing agents down to 0.8 mg NH₃-N/L or in the presence of a large excess (50 to 100 times) of complexing agent. Known addition is a convenient check on the results of direct measurement.

Scope and Application

This method is applicable to the measurement of 0.03 to 1400 mg NH₃-N/L in potable and surface waters and domestic and industrial wastes. High concentrations of dissolved ions affect the measurement, but color and turbidity do not. Sample distillation is unnecessary.

Applicable Concentration Range

0.03 - 1400 mg NH₃-N/L (See 4500-NH₃ D)

Interferences

Amines are a positive interference. This may be enhanced by acidification. Mercury and silver interfere by complexing with ammonia, unless the NaOH/EDTA solution is used.

Quality Control Requirements

See Section 4020 Quality Assurance/Quality Control.

Sample Handling

Refrigerate at 4 degrees C for samples to be analyzed within 24 h. Preserve samples high in organic and nitrogenous matter, and any other samples for longer storage, by lowering pH to 2 or less with conc H2SO4. See 4500- NH3 D.

Most reliable results are obtained on fresh samples. If samples are to be analyzed within 24 h of collection, refrigerate unacidified at 4 degrees C. For preservation up to 28 d, freeze at -20 degree C unacidified, or preserve samples by acidifying to pH < 2 and storing at 4 degree C. If acid preservation is used, neutralize samples with NaOH or KOH immediately before making the determination. CAUTION: Although acidification is suitable for certain types of samples, it produces interferences when exchangeable ammonium is present in unfiltered solids. See 4500-NH3 A.

Maximum Holding Time

28 days (acidified or frozen); 24 hours (refrigerated) (See 4500 NH3 A)

Relative Cost

Less than $50

Sample Preparation Methods

This method has 2 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Ammonia(7664-41-7) Ammonia Anhydrous ammonia Nitrogen, ammonia	0.800 mg/L	108% Rec (SL)	1.32 SD (ML)
Total Kjeldahl nitrogen(E-10264) Kjeldahl nitrogen, total Nitrogen, Kjeldahl, total Nitrogen, organic TKN Total Kjeldahl nitrogen	N/A	N/A	N/A

Precision Descriptor Notes:	In 38 water samples analyzed by both the phenate and the known-addition ammonia-selective electrode method, the electrode method yielded a mean recovery of 102% of the values obtained by the phenate method when the NH3-N concentrations varied between 0.30 and 0.78 mg/L. In 57 wastewater samples similarly compared, the electrode method yielded a mean recovery of 108% of the values obtained by the phenate method using distillation when the NH3-N concentrations varied between 10.2 and 34.7 mg N/L. In 20 instances in which two to four replicates of these samples were analyzed, the mean standard deviation was 1.32 mg N/L. In three measurements at a sewer outfall, distillation did not change statistically the value obtained by the electrode method. In 12 studies using standards in the 2.5- to 30-mg N/L range, average recovery by the phenate method was 97% and by the electrode method 101%.
Detection Level Note:	Lowest level of stated method range (See 4500-NH₃ D).

Precision Descriptor Notes:

In 38 water samples analyzed by both the phenate and the known-addition ammonia-selective electrode method, the electrode method yielded a mean recovery of 102% of the values obtained by the phenate method when the NH3-N concentrations varied between 0.30 and 0.78 mg/L. In 57 wastewater samples similarly compared, the electrode method yielded a mean recovery of 108% of the values obtained by the phenate method using distillation when the NH3-N concentrations varied between 10.2 and 34.7 mg N/L. In 20 instances in which two to four replicates of these samples were analyzed, the mean standard deviation was 1.32 mg N/L. In three measurements at a sewer outfall, distillation did not change statistically the value obtained by the electrode method. In 12 studies using standards in the 2.5- to 30-mg N/L range, average recovery by the phenate method was 97% and by the electrode method 101%.

Detection Level Note:

Lowest level of stated method range (See 4500-NH₃ D).

Revision	PDF/Link
Standard Methods Online
Standard Methods 18th Edition (1992)
Standard Methods 19th Edition (1995)
Standard Methods 18th, 19th, 20th ed.

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Standard Methods: 4500-NH₃ E: Ammonia by Selective Electrode Methods Using Known Addition

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Standard Methods: 4500-NH3 E: Ammonia by Selective Electrode Methods Using Known Addition

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Standard Methods: 4500-NH₃ E: Ammonia by Selective Electrode Methods Using Known Addition