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FIAlab Instruments, Inc.
14450 NE 29th Place STE 113
Bellevue, WA  98007 USA

Voice: 425-376-0450
Fax: 425-376-0451
fialab@flowinjection.com

              


              


Nitrate/Nitrite  

FIAlab standard method for the nitrite and nitrate in fresh or salt waters  using the FIAlab-2500/2600/2700 system.

Assay Typical Throughput Concentration Range Notes
Nitrate (Mid to High) 180 samples/hour 0.02 to 200 mg (N)/L 1 cm flowcell
Nitrite (Mid to High) 220 samples/hour 0.005 to 100 mg (N)/L  
Nitrate (Low) 60 samples/hour 0.002 to 10 mg (N)/L 10 cm flowcell
Nitrite (Low) 80 samples/hour 0.0005 to 5 mg (N)/L
Nitrate (Ultra Low) 45 samples/hour 0.0004 to 1 mg (N)/L 50 cm flowcell
Nitrite (Ultra Low) 55 samples/hour 0.0001 to 0.5 mg (N)/L

 

 Principle:

 The determination of nitrate and nitrite concentration is one of the most frequent needs in environmental investigations.  Numerous analytical methods exist and the reduction of nitrate to nitrite for quantitative colorimetry has proven to be both sensitive and very reliable for flow injection analysis.  A copperized cadmium column is used to catalyze the reduction of nitrates into nitrites in a reproducible and quantitative fashion.  Nitrites will react with sulfanilamide to form azo dyes that will then couple with N- (1-Naphthyl) ethylenediamine dihydrochloride to form magenta colored solution.  This azo dye solution can be quantified at 540 nm and is proportionate to the quantity of nitrate/nitrite present in the initial sample.

 

 Comments:
 
To convert the manifold to process nitrate, connect a cadmium column between the FIA LOV Manifold ports labeled “B”. If there is a heater installed on the unit, the heater should be turned off or the coil removed from the heated waterbath. Two reagents are utilized for nitrate, and one for nitrite. The flowrate of the pump should be set to 60. Recommended wavelengths 540 nm primary and 650 nm reference.
 
For Mid to High nitrate/nitrite assays, make the sample loop from three inches of tubing (.03” ID) and use a 1 cm flowcell.   
 
For Low concentration assays make the sample loop from eight inches of tubing (.03” ID) and use a 10 cm flowcell.   
For Ultra Low concentration assays make the sample loop from 36 inches of tubing (.03” ID) and use a 50 cm flowcell. 

Extended high dynamic range can be achieved by using a secondary suboptimal wavelength of 585 nm.

For seawater based assays, standards and carrier should match the salinity of the samples as close as possible.   
Interferences:
  1. Chlorine can interfere by oxidizing the reduction column.
  2. High concentrations of iron, copper or other metals cause negative interference. EDTA is added to the buffer to reduce this interference.
  3. Oil and grease will coat the surface of the cadmium. This interference is eliminated by pre-extracting the sample with an organic solvent.
  4. Sample turbidity/color may interfere. Pre-filtration with a membrane filter should help.

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: 1.6 M Ammonium Chloride Buffer (for nitrate only).

Note - For nitrite, plug this R1 port with an included Teflon Plug

500 ml TOTAL: Balance with Degassed DI water

43 grams Ammonium chloride

0.50 grams disodium ethylenediamine tetraacetic acid (EDTA) [372.24 FW]  (only if metals may be present)
 ~1 grams Sodium Hydroxide Pellets as needed

Place 400 cc of water into a volumetric flask and add the ammonium chloride and EDTA.  Mix until dissolved.  Adjust the pH of this solution to ~8.5 using sodium hydroxide pellets.  Add water to fill flask to 500mL.

CAUTION: Ammonium chloride sometimes may contain significant amounts of nitrate.

Reagent 2: Colorimetric Sulfanilamide Solution.

LC13280  Color reagent for nitrate  From Fisher Sci (search for LC13280 at www.fischersci.com ) .    This reagent works for nitrate and nitrite.

 

Alternative Reagent 2:

20 grams Sulfanilamide [172.21 FW]

50 ml 85% Conc. Phosphoric Acid  (H3PO4)

0.50 grams N-1-naphthylethylenediamine dihydrochloride [259.18 FW]

500 ml TOTAL: Balance with Degassed DI water

Mix well and store in dark bottle.

Cadmium Column: 
Cadmium column can be prepared/packed by user, or
purchased ready for use from the following sources (for nitrate only).  For nitrite assays, use a bridge of 0.03" ID tubing (~4 inches) in place of the column.

 

1)     50237A or CC120 Cadmium Column for nitrate reduction column  (or)

2)     Prepare your own Cadmium (see section 8 in FIAlab Operation Manual)

 

 Standards:

100ml ICNAT-100 (nitrate standard)

100ml ICNIT-100 (nitrite 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