Method 350.3

Nitrogen, Ammonia (Potentiometric, Ion Selective Electrode)

This method is applicable to the measurement of ammonia-nitrogen in drinking, surface and saline waters, domestic and industrial wastes. This method covers the range from 0.03 to 1400 mg ammonia-nitrogen/L. Color and turbidity have no effect on the measurements, thus, distillation may not be necessary. The ammonia is determined potentiometrically using an ion selective ammonia electrode and a pH meter having an expanded millivolt scale or a specific ion meter. The ammonia electrode uses a hydrophobic gas-permeable membrane to separate the sample solution from an ammonium chloride internal solution. Ammonia in the sample diffuses through the membrane and alters the pH of the internal solution, which is sensed by a pH electrode. The constant level of chloride in the internal solution is sensed by a chloride selective ion electrode which acts as the reference electrode.

(EPA: Office of Water)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   None noted in method.
Preservatives:   Samples may be preserved with 2 mL of concentrated sulfuric acid to a pH <2 per liter and stored at 4°C.
Required Preps:   None noted in method.
Collection Method:   Grab; Samples should be collected in plastic or glass bottles.
Analytical Methodology:   Ammonia selective electrode; Electrometer (pH meter) with expanded mV scale or a specific ion meter.
Documentation:   350.3

Analyte List*

Analyte Formula CAS Number Detection Limit

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.