Nitrite aquarium

Nitrite Tap, ground, harbour, aquarium waters Octadecyl-bonded silica gel (Cis) disks UV—Vis (diffuse reflectance halogen-tungsten lamp) 0.1 ng mL 1 Flow injection system SPE at the detection unit sandwich optrode [503]... 

Students at Harvey Mudd College monitor a saltwater aquarium to study the chemistry of a marine ecosystem. When fish and food are introduced into the aquarium on day 0 in panel a, organic compounds are metabolized to produce NH3. Anunonia is toxic to marine animals when the level exceeds 1 ppm but, fortunately, it is removed by Nitrosomonas bacteria, which colonize the aquarium filter and oxidize NH3 to nitrite (NO2). Alas, NO2 is also toxic at levels above 1 ppm, but it is further oxidized to nitrate (NO J) by a second colonization of Nitrobacter bacteria. The natural process of oxidation of NH3 to NO2 and NOJ is called nitrification. 

For a compound to be analyzed by spectrophotometry, it must absorb electromagnetic radiation, and this absorption should be distinguishable from that of other species in the sample. Biochemists assay protein solutions in the ultraviolet region at 280 nm, where the aromatic amino acids tyrosine, phenylalanine, and tryptophan (Table 11-1) have maximum absorbance. Common salts, buffers, and carbohydrates have little absorbance at this wavelength. In this section, we use Beer s law for a simple analysis and then discuss the measurement of nitrite in an aquarium. 

Box 6-1 stated that nitrogen compounds derived from animals and plants are broken down to ammonia hetm>trophic bacteria. Ammonia is oxidized first to nitrite 02 ) and then to nitrate (NO J) by nitrifying bacteria. In Section 6-3 we saw how a permanganate titration was used to standardize a nitrite stock solution. The nitrite solution is used here to pr xue standards for a spectrophotometric analysis of nitrite in aquarium water. 

The aquarium nitrite analysis is based on a reaction whose colored product has an absorbance maximum at 543 nm (Figure 18-10) ... 

Analyze duplicate samples of unknown aquarium water that has been filtered prior to dilution to remove suspended solids. Several trial dilutions may be required before the aquarium water is dilute enough to have a nitrite concentration that falls within the calibration range. 

From the data in Table 18-2, find the molarity of nitrite in the aquarium. 

SOLUTION The average corrected absorbance of unknowns in Table 18-2 is 0.276. Substituting this value into Equation 18-8 gives ppm of nitrite nitrogen in the aquarium ... 

A nitrite analysis conducted by the procedure in Section 18-4 gave data in the table on the next page. Fill in corrected absorbance, which is measured absorbance minus the average blank absorbance (0.023). Construct a calibration line to find (a) ppm nitrite nitrogen uncertainty and (b) molar concentration of nitrite in the aquarium. Use the average blank and the average unknown absorbances. 

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