The WestCo SmartChem 200 discrete analyzer is an automated spectrophotometer. The SmartChem 200 is capable of a number of different measurements, but its primary function is the measurement of various forms of nitrogen (NO2, NO3, and NH4) and phosphorus (PO4) in solution.
Based on the chemistries used in continuous flow analysis, discrete analysis is fully automated and "flowless". An automated arm collects samples 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 at a specified wavelength.
Nitrate is reduced quantitatively to nitrite by a cadmium catalyst. The reduced nitrite, 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 may be measured spearately 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.
