Morton College

Determining Nitrate and Nitrite Sequentially Using a Nitrite Ion Selective Electrode

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Courtesy of Morton College

ABSTRACT

Reliable analysis for NO3- and NO2- contained in wastewater, soils and reclaimed water is extremely important as these constituents can easily leach into Florida’s groundwater system. The maximum limit for nitrate, NO3- is 10 ppm, and for nitrite, NO2- it is 1.0 ppm. Therefore close monitoring of these nitrogen compounds is necessary. Determinations are generally performed using expensive automated equipment, i.e., a Lachat flow injection analyzer (Hach Co., Loveland, CO). Alternatively, nitrate and nitrite can also be determined via there respective ion selective electrodes (ISE), although the nitrate ISE is of limited use due to its multiple interferences. A newly developed method enables the nitrate ion along with the nitrite ion to be determined sequentially with the nitrite ISE. The analysis is achieved by converting nitrate ion, using the dual reducing power of trivalent chromium plus hydrosulfite ion (dithionite), to nitrite ion. The electrode will first measure the initial nitrite ion concentration, then continue to measure any nitrate that is reduced to nitrite ion. Nitrate analysis performed on a NO2- electrode, based on chemical reduction combines the most desirable features of a good analytical tool joined with the cost and ease of use of an ISE. The comparison of this electrode method to a known procedure is described here.

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