Consecutive estimation of nitrate and nitrite ions in vegetables and fruits by electron paramagnetic resonance spectrometry

Consecutive estimation of nitrate and nitrite in vegetables and fruits by electron paramagnetic resonance (EPR) spectrometry is described, based on the selective reactions of nitrate and nitrite ions to yield a stoichiometric amount of the EPR-active mononitrosyldiethyldithiocarbamate complex of iron in aerobic conditions. Since, nitrogen monoxide and dioxide (which may be present in the air) give the same reaction, the detection limit depends on their background concentration in the air. The EPR response is found to be linear up to 2500 mug of NO2- and 16 000 mug of NO3-. The applicability of EPR spectrometry for estimation of both nitrate and nitrite content is demonstrated by the analysis of 18 vegetables and fruits, available in the local markets, grown with the use of mineral fertilizers. The results obtained are compared with those for some "home-grown" vegetables with the use of organic fertilizers.