The
WestCo SmartChem 200 discrete analyzer is an automated spectrophotometer
that replaces the Alpkem Flow Solution IV within the EM-1 facility.
The Alpkem will only be used occasionally for long nitrate runs, or as a
backup to the discrete analyzer. The SmartChem 200 is capable of a
number of different measurements, but its primary function will be to
measure various forms of nitrogen and phosphorus in solution.
While based on the similar
chemistries as continuous flow analysis, discrete analysis is fully
automated and "flowless". A manual arm collects sample and reagents
and dispenses them in a cuvette. The cuvette resides in a heated
carousel wheel where the chemical reaction is allowed to proceed to the
development of a colored product. The optical density of the reaction
product is then measured.
Nitrate is reduced quantitatively to nitrite by a
cadmium column. The nitrite formed, in addition to any nitrite
originally present in the sample, is diazotized with sulfanilamide and
subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride.
The resulting colored azo dye is colorimetrically detected at 550 nm.
Nitrite singly may be measured by performing the same analysis without
the cadmium column.
Ammonium reacts with salicylate and hypochlorite in
a buffered alkaline solution in the presence of sodium nitroferricyanide
(pH 12.8-13) to form the salicylic acid analog of indophenol blue. The
blue-green color produced is measured at 660 nm.
Orthophosphate reacts with molybdenum VI and
antimony III in an acid medium to form an antimony-phospho-molybdate
complex. This complex is subsequently reduced with ascorbic acid to
produce a blue color which is measured at 880 nm.
