Standard Methods: 4500-NH3 G:  Ammonia by Automated Phenate

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Official Method Name
4500-NH3 G. Automated Phenate Method
Current Revision
Standard Methods Online
Media
WATER
Instrumentation
Automated Spectrophotometer
Method Subcategory
Inorganic
Method Source
  Standard Methods
Citation
  Standard Methods Online - Standard Methods for the Examination of Water and Wastewater
Brief Method Summary
Alkaline phenol and hypochlorite react with ammonia to form indophenol blue that is proportional to the ammonia concentration. The blue color formed is intensified with sodium nitroprusside.
Scope and Application
Ammonia nitrogen can be determined in potable, surface, and saline waters as well as domestic and industrial wastewaters when photometric measurement is made at 630 to 660 nm in a 10- to 50-mm tubular flow cell at rates of up to 60 samples/h. Determine higher concentrations by diluting the sample.
Applicable Concentration Range
0.02 - 2.0 mg/L
Interferences
Seawater contains calcium and magnesium ions in sufficient concentrations to cause precipitation during analysis. Adding EDTA and sodium potassium tartrate reduces the problem. Eliminate any marked variation in acidity or alkalinity among samples because intensity of measured color is pH-dependent. Likewise, insure that pH of wash water and standard ammonia solutions approximates that of sample. Remove interfering turbidity by filtration. Color in the samples that absorbs in the photometric range used for analysis interferes.
Quality Control Requirements
See Section 4020 Quality Assurance/Quality Control.
Sample Handling
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
4500-NH3 B (Preliminary Distillation)