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o-Phenylenediamine has been used as a reagent to quantify nitrites/nitrates in a variety of sample matrices. The method is based on the cyclization reaction between o-phenylenediamine and nitrite in acid medium. The amine undergoes diazotization with nitrite in the presence of acid to form the diazonium ion, which subsequently cyclizes to yield yellowish orange benzotriazole at room temperature with an absorption maximum at 450 nm. The formed dye has been separated, purified, and characterized by IR, NMR, and spectroscopy techniques. The parameters of the reaction between amine and nitrite have been optimized. The effect of interfering ions on the determination of nitrites/nitrates has been described. The developed method has been applied for the determination of residual NO2 gas present in the ambient air after fixing it as a nitrite ion using sodium arsenite as a trapping medium. The dye formed has been extracted into organic solvent to improve the detection limit during the measurement of low levels of ambient NO2 in air. The method obeyed Beer's law in the concentration range 0-250 µg in aqueous medium and 0-50 µg in organic medium with molar absorptivity of 4.09 × 104 L mol-1 cm-1 and 4.3 × 104 L mol-1 cm-1 respectively. Nitrate is determined by reducing it to nitrite after passing through the copperized cadmium reductor column. The developed method has been applied to determine nitrite/nitrate levels in water, soil, and biological samples. [ABSTRACT FROM AUTHOR]

A simple and sensitive spectrophotometric method for the determination of nitrogen dioxide in ambient air and nitrite/nitrate in water and soil samples has been developed. Nitrogen dioxide in air has been fixed as nitrite ion using alkaline sodium arsenite as absorbing medium. The method is based on the reaction of nitrite with aminophenyl benzimidazole in acid medium to form diazonium ion, which is coupled with N-(1-naphthyl)ethylenediamine dihydrochloride to form an azo dye with an absorption maximum at 555 nm in aqueous phase. The method obeys Beer's law in the concentration range 0-10 µg of nitrite in 25 ml solution. The molar absorptivity has been found to be 6.3×104 l mol-1 cm-1. The dye can be extracted quantitatively into isoamyl alcohol under alkaline condition and the addition of methanolic hydrochloric acid restores the original dye colour. Beer's law is obeyed in the concentration range 0-2 µg of nitrite with a detection limit of 0.009 µg. The effect of interfering species has been studied and the developed method has been applied to determine trace levels of nitrogen dioxide in ambient air and the results have been compared with the standard method. It is also applied to measure the nitrite/nitrate levels of surface and ground water samples collected from lakes, tube wells as well as soil samples. [ABSTRACT FROM AUTHOR]

Copper oxide impregnated glassy carbon spheres (Cu x OGCS where x = 1or2) modified basal plane pyrolytic graphite electrode (Cu x OGCS-BPPGE) was demonstrated as electrochemical interface for nitrite/nitrate sensing. The Cu x OGCS were synthesized by impregnating glassy carbon spheres GCS with 0.5 M CuNO 2 solution followed by thermal treatment at 823 K. Electrochemical and spectroscopic studies of the composites confirms the copper oxide formation during synthesis. The electrocatalytic oxidation/reduction studies of the nitrite/nitrate on a Cu x OGCS-BPPG electrode has been studied by cyclic voltammetry (CV). The detection limits obtained were 1.032 μg L−1 for nitrate and 2.038 μg L−1 for nitrite respectively. The sensitivity of the method was about 1500 μA μM−1 cm−2 for nitrite determination. It has been demonstrated that the composite electrode can be used to analyze nitrate/nitrite in soil and fruit juice samples. Schematic diagram showing steps involved in CuO impregnated GCS synthesis. Image 1042 • CuO impregnated glassy carbon spheres was synthesized using simple method. • The materials shows excellent electro catalytic oxidation of nitrite. • The materials shows excellent electro catalytic reduction of nitrate. • The proposed method can be used for speciation of nitrate/nitrite. [ABSTRACT FROM AUTHOR]