Standard Methods: 4500-NH₃ D: Ammonia by Selective Electrode

Summary
Analytes
Revisions
Data and Sites

Official Method Name

4500-NH₃ D. Ammonia-Selective Electrode Method

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

The ammonia-selective electrode uses a hydrophobic gas-permeable membrane to separate the sample solution from an electrode internal solution of ammonium chloride. Dissolved ammonia (NH₃(aq) and NH₄+) is converted to NH₃(aq) by raising pH to above 11 with a strong base. NH₃(aq) diffuses through the membrane and changes the internal solution pH that is sensed by a pH electrode. The fixed level of chloride in the internal solution is sensed by a chloride ion-selective electrode that serves as the reference electrode. Potentiometric measurements are made with a pH meter having an expanded millivolt scale or with a specific ion meter.

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

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.

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	0.030 mg/L	105% Rec (ML)	14.00 % RSD (ML)			0.80 mg/L
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:	The data presented in NEMI were generated by analyzing fortified distilled water samples at 12 laboratories. Additional data from the study are available in the method - contamiation appeared to be a substantial issue at levels below 0.8 mg/L. In addition, for the ammonia-selective electrode in a single laboratory using surface water samples at concentrations of 1.00, 0.77, 0.19, and 0.13 mg NH3-N/L, standard deviations were +/-0.038, +/-0.017, +/-0.007, and +/-0.003, respectively. In a single laboratory using surface water samples at concentrations of 0.10 and 0.13 mg NH3-N/L, recoveries were 96% and 91%, respectively. The results of an interlaboratory study involving 12 laboratories using the ammonia-selective electrode on distilled water and effluents are summarized in a table in the method.
Detection Level Note:	Lowest level of stated method range.

Precision Descriptor Notes:

The data presented in NEMI were generated by analyzing fortified distilled water samples at 12 laboratories. Additional data from the study are available in the method - contamiation appeared to be a substantial issue at levels below 0.8 mg/L. In addition, for the ammonia-selective electrode in a single laboratory using surface water samples at concentrations of 1.00, 0.77, 0.19, and 0.13 mg NH3-N/L, standard deviations were +/-0.038, +/-0.017, +/-0.007, and +/-0.003, respectively. In a single laboratory using surface water samples at concentrations of 0.10 and 0.13 mg NH3-N/L, recoveries were 96% and 91%, respectively. The results of an interlaboratory study involving 12 laboratories using the ammonia-selective electrode on distilled water and effluents are summarized in a table in the method.

Detection Level Note:

Lowest level of stated method range.

Revision	PDF/Link
Standard Methods Online
As Method 4500-NH3 F or G in Standard Methods 18th Edition (1992)
Standard Methods 19th Edition (1995)
Standard Methods 18th, 19th, 20th ed.

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Standard Methods: 4500-NH₃ D: Ammonia by Selective Electrode

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Standard Methods: 4500-NH₃ D: Ammonia by Selective Electrode