Assay

Typical Throughput

Concentration Range

Notes

Nitrate (Mid to High)

Nitrite (Mid to High)

180 samples/hour

220 samples/hour

0.03 to 200 mg (N)/L
 

0.005 to 100 mg (N)/L
 

Nitrites react with sulfanilamide to form azo dyes that will then couple with N- (1-Naphthyl) ethylenediamine dihydrochloride to form magenta colored solution.

A copperized cadmium column converts nitrate to nitrite.  Dynamic Range extended using selected choices of wavelengths.

Nitrate (Low)

Nitrite (Low)

60 samples/hour

80 samples/hour

0.003 to .9 mg (N)/L
 

 
0.0005 to .18 mg (N)/L

Identical chemistry as above, however utilizes a 10 cm long optical path flow cell.

Nitrate  - Reagent Free

60 samples/hour

1 to 100 mg (N)/L
 

Nitrate has a very strong absorption at 214 nm in the UV range.   This approach is limited to cleaner samples, e.g., drinking water, where suspended matter and other interferences won't be problematic.

Ammonia (Mid to High)

120 samples/hour

0.5 to 200 mg (N)/L NH₃
 

Ammonia in water can be determined using the standard Salicylate method. This method requires a heated reaction coil. 

Ammonia (Low)

80 samples/hour

0.01 to 10 mg (N)/L NH₃
 

Identical chemistry as above, however utilizes a 10 cm long optical path flow cell.

Ammonia (Ultra Low)

30 samples/hour

0.001 to 0.5 mg (N)/L NH₃
 

Fluorometric ammonium (OPA) analysis.  Required hardware includes PMT-FL and either the FIAlab-2500 or FIAlab-2700.  Also requires a flowthrough heater.

Ammonia by Gas Diffusion

50 samples/hour

1 to 1000 mg (N)/L NH₃
 

Ammonia sample is injected into sodium hydroxide stream to form NH3.   The NH3 moves across a gas-permeable membrane into a collector stream containing bromothymol blue.

Phosphate  (Mid to High)

Method compatible with Bray and Olsen Bicarb soil extraction samples.  Similar method is compatible with total phosphate assays.

120 samples/hour

0.1 to 25 mg
(Phosphate)

Orthophosphates react directly with molybdate anions to form a yellow-colored phosphomolybdate complex.  This complex is then reduced by ascorbic acid to create a molybdenum blue species that has a broad absorbance range from 700nm to 900nm. 

Phosphate  (Low)

60 samples/hour

0.01 to 2.5 mg
(Phosphorous)

Identical chemistry as above, however requires heated reaction coil and a 10+ cm  flowcell.

Chloride

120 samples/hour

1 to 50 mg Cl-/L

The chloride assay is based on the liberation of the thiocyanate ion (SCN) from mercuric thiocyanate, through sequestration of mercury by the chloride ion, to form un-ionized, but soluble mercuric chloride. The liberated SCN then reacts with the ferric ion to form highly colored ferric thiocyanate.

Chloride

60 samples/hour

0.1 to 5 mg Cl-/L

Identical chemistry as above, however utilizes a 10 cm long optical path length flowcell.

Sulfate

120 samples/hour

5 to 500 ppm

Sulfate forms a precipitated with barium chloride and scatters light proportional to the concentration.

Iron

140 samples/hour

0.1 to 100 ppm

1,10-phenanthroline chelation chemistry to Fe²⁺. This Fe-complex has an absorbance maximum around 510nm.