Spectrophotometric determination of nitrite in sea water with employment of the standard additions method. Interactive laboratory exercise.
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In this exercise, the determination of nitrite in sea water by visible spectrophotometry is carried out. The nitrite anion reacts in acidic medium with sulfanilamide with formation of a diazonium salt, which, in turn, by a coupling reaction with N (1-naphthyl) ethylenediamine dihydrochloride, gives a red azo compound. This azo derivative absorbs at 540 nm. The steps of the analytical procedure are described and the standard additions method (SAM) is employed to find the nitrite concentration in the sample. The data are randomly generated, and the result of the analysis, expressed in ppb of N-NO2-and must be calculated from the equation of the SAM graph, adjusted by least squares. The exercise is a simulation that helps to understand the protocol of analysis and to carry out the procedure in the laboratory session more efficiently.