Photo-Fenton approach for the determination of organic nitrogen in rainwater

Abstract

The importance of taking the organic forms of nitrogen (ON) into account when estimating atmospheric nitrogen deposition has been known for a long time. However, there is still only a modest amount of data on organic nitrogen in rainwater worldwide, largely due to the difficulties and uncertainties imposed by the available analytical methods. This work offers a simple, low cost, and reliable method for the determination of ON in rainwater, based on the photo-Fenton process under UV irradiation. The recovery of ON was determined using individual solutions of urea, serine, glycine, and histidine, as well as a mixture of all these compounds plus arginine. Close to 100% organic nitrogen recoveries were obtained for solutions containing 50 μmol N L−1, using addition of 50 μmol L−1 Fe2+ and 2.0 mmol L−1 H2O2, with adjustment of the pH to ∼2.5 and irradiation for 90 min. The average reagent blank was <2.0 μmol N L−1. The homemade reactor employed a 400 W high pressure mercury lamp, from which the external bulb had been manually removed. The reactor ventilation was controlled in order to maintain the temperature at ∼85 °C. The precision of the method ranged from 1.3 to 5.7%, based on ON recovery. Rainwater collected on an event basis in Ribeirão Preto (São Paulo State, Brazil) presented ON concentrations from 4.1 to 34.3 μmol L−1 (n = 18), corresponding to 13–45% of the total nitrogen, with an average contribution of 33%. Precision of ≤7.0% was obtained for the analysis of ON in rainwater.