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Ammonia (Water Based Samples)  

FIAlab standard method for the ammonia assay in fresh/salt waters and KCL soil extracts  using the FIAlab-2500/2600/2700 system.
Assay Typical Throughput Concentration Range Notes
Ammonia (Mid to High) 120 samples/hour 0.5 to 200 mg (N)/L NH3 1 cm flowcell
Ammonia (Low) 80 samples/hour 0.01 to 10 mg (N)/L NH3 10 cm flowcell
Ammonia (Ultra Low) 40 samples/hour 0.002 to 2 mg (N)/L NH3 50 cm flowcell

 Note: For an alternative ultra low method please review the fluorometric OPA approach.

 Principle:

This method was optimized to meet the needs of environmental monitoring, where water samples are tested to conform to the 10mg (N)/L MCL USEPA requirement.  Low ammonium levels can be determined in FIA by using the salicylate method.  The salicylate method is a variation of the Berthelot-Phenate method but does not require the use and disposal of toxic phenol.  The salicylate method involves a three-step reaction sequence.  The first reaction step involves the conversion of ammonia to monochloroamine by the addition of chlorine.  The monochloroamine then reacts with salicylate to form 5-aminosalicylate.  Finally, the 5-aminosalicylate is oxidized in the presence of sodium nitroferricyanide to form a blue-green colored dye that absorbs light at 650nm.

 Comments:
 

Water Bath Heater should be turned on to 60 C.  The flowrate of the pump should be set to 45. The FIA LOV connections B should be bridged by short green tubing.   Recommended wavelengths: 650 nm primary and 525 nm reference.   825 nm can also be used as the reference.

For most ammonia assays (> 0.5 ppm) make the sample loop from three inches of green tubing (.03” ID).

Low Concentration Assays:  For low concentrations (below 0.5 ppm) consider using the 10 cm flowcell.   Also for lower concentrations (0.01 to 0.2 ppm) use longer sample loop (e.g., 12 inches of .03” ID tubing).   For the low end of this range, care must be taken to use clean glassware and extended washouts of tubing  on the system to prevent crossover contamination.  

For ultra low concentrations use a 36" sample loop.

Interferences:

Sulfide will intensify the blue-green color and should be removed from the sample if possible.  Hydrazine and glycine like sulfide can also intensify the color. High sample turbidity will give significant erroneous results and may need to be pre-filtered or run utilizing a different ammonia method.  Iron will also interfere with the analysis, but can be eliminated by doping the calibrations samples with the same level of iron present in the sample.  To a lesser extent the following ions may also interfere: sulfates (>300 ppm), phosphates (>100 ppm), nitrates (>100 ppm), nitrites (>12 ppm), calcium (>1000 ppm) and magnesium (>6,000 ppm).

Reagents:

Carrier: 
The carrier should be matrix matched to the sample, i.e., salt content for seawater samples, and KCL content for soil extracts.

 
Reagent 1:  Hypochloride Solution.

10-mL of a 6% Sodium hypochloride solution (common household bleach)

5-grams NaOH (s)

Balance Degassed DI water (1 L)

 

Place a 10ml solution of bleach into a 1-liter volumetric flask and fill with 700-mL of degassed DI water.  Dissolve all other chemicals and fill flask to the 1-liter mark.

 

Reagent 1 degrades with time, should be prepared daily.

 

Note: If bubbles become an issue, sticking in the flowcell and other parts of the manifold then add 1-gram Brij-35 (detergent) to Reagent 1.

 

Reagent 2:  Salicylate/Catalyst Solution.

100-grams Sodium Salicylate [160.11 FW]

0.40-grams Sodium Nitroferricyanide (III) dihydrate [297.95 FW] catalyst

5-grams NaOH (s)

Balance Degassed DI water(1 L)

 

Place the sodium salicylate into a 1-liter volumetric flask and mix with 700-mL of degassed DI water until dissolved.  Add the sodium nitroferricyanide and mix until dissolved. Add NaOH to adjust the pH to the ~12.0 range.  Add the Brij 35, mix and fill flask to the mark.  Transfer solution into a dark, airtight glass bottle for maximum longevity. Prepare fresh weekly due to limited storage life.

 

 Standards:

100ml ICAMU-100  (ammonia standard)

Source: 727-524-7732 - www.exaxol.com 

Please email or phone FIAlab Instruments for additional product information.
 Email: fialab@flowinjection.com, Voice: 425-376-0450 or 1-800-963-1101,  Fax: 425-376-0451