Aquarium nitrite analysis

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

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. 

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. 

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