Determinations of Nitrate and Nitrite in the Rappahannock and James with UV/Vis Spectroscopy

By Rebecca Bowers, Sophie Elliot, Ksenia Mangino, David Nichols

Faculty Mentor: Sarah Smith


Excess fertilizer runoff or waste containing ammonium nitrate can cause an uptick in algal blooms in waterways, which leads to rivers becoming oxygen starved and nutrient deficient. While the EPA limits quantify dangerous levels of nitrate (NO3-) and nitrite (NO2-) in water separately, there is no clear limit for both existing in a sample. The goal was to develop a method to analyze total NO3- and NO2- concentrations in water sources through reduction of nitrate using a reduction column and an absorbance spectroscopy UV-Vis Spectrometer. Since NO3- cannot attach itself to a chromophore until it is reduced to NO2-, a chromophore was added to high
concentration samples of sodium nitrite (NaNO2) using a Greiss Reagent (N-(1-naphthyl)ethylenediamine and sulfanilic acid) to make standards. The standards with known nitrite concentrations were analyzed to determine the maximum wavelength and create a calibration curve. Due to initial nitrogen testing indicating high levels of NO3-, however; river water from the Rappahannock and James River needed to be reduced using a zinc reduction
column and chelation agent (EDTA) in order to obtain an accurate measurement of total concentrations of both NO2- and reduced state NO3-. Unknowns were analyzed against the calibration curve to determine nitrite concentration in different aquatic environments with close proximity to potential contamination sources. With or without reduced nitrate, it is predicted that the water in stagnant canals or near large urban areas such as golf courses will have higher concentrations of nitrite.


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